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A photoionisation mass spectrometric study of some stereoisomers Akhtar, Zinat Mahal (Mia) 1972

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11 "/_uo A PHOTOIONISATION MASS SPECTROMETRIC STUDY OF SOME STEREOISOMERS BY ZINAT MAHAL (MIA) AKHTAR B.Sc. (Hon.)> University of British Columbia, 1967 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in the Department of CHEMISTRY We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA April , 1972 In present ing t h i s thes is in p a r t i a l f u l f i l m e n t of the requirements fo r an advanced degree at the Un i ve rs i t y of B r i t i s h Columbia, I agree that the L ib rary sha l l make i t f r e e l y a v a i l a b l e fo r reference and study. I fu r ther agree that permission for extens ive copying of th i s t h e s i s fo r s c h o l a r l y purposes may be granted by the Head of my Department or by h is representat i ves . It is understood that copying or p u b l i c a t i o n of t h i s thes is fo r f i n a n c i a l gain sha l l not be allowed without my wr i t ten permiss ion. Department of Chemistry  The Un ivers i t y of B r i t i s h Columbia Vancouver 8, Canada Date 1st May, 1972. - i i -ABSTRACT Photoionisation mass spectrometry has been used to study a number of stereoisomeric systems. Low resolution spectra were obtained for the epimers of 4-t-butylcyclohexanol, 4-t-butylcyclohexyl acetate, 4-t-butylcyclohexyl methyl ether and the 4, 3, and 2 methyl substituted 0 cyclohexanols using the He 584 A radiation and the Lyman a radiation for ionisation. Analogues labelled with deuterium at specific positions were also prepared for a l l the molecules studied. The major fragments in the low resolution spectra were mass measured to determine the elemental composition. Possible fragmentation pathways are postulated for the different molecules studied making use of the information obtained from the labelled analogues, together with the high resolution results and any observed ions due to metastable transitions. The epimers of 4-t-butylcyclohexanol and 4-t-butylcyclohexyl methyl ether give rise to mass spectra which differ in the relative abundances of both the molecular ion and other major ions. The observed differences are explained in terms of the stereochemical arrangement of the atoms and groups in the respective isomers. The spectra obtained for cis and trans 4-t-butylcyclohexyl acetate are almost identical. The similarity i s proposed to be due to the intervention of different mechanisms from that observed in the corresponding alcohols and ethers. An attempt is also made to discuss the results obtained for the various methyl cyclohexanols both in terms of the spatial arrangement and the position of the substituent. - i i i -'TABLE OF CONTENTS „:. Page ABSTRACT i i ACKNOWLEDGEMENT x v i i INTRODUCTION 1 THEORETICAL . 8 (a) Mass Spectrometer 8 (b) Metastable lens 9 (c) Photoionisation 11 (d) Formation of Ions 12 (e) Quasi Equilibrium Theory 16 (f) Qualitative Theories of Mass Spectra: "Mechanistic Approach" 17 EXPERIMENTAL 21 PART A. Synthesis and Purification of Compounds 21 PART B. Mass Spectra 38 RESULTS 42 A. Cis and trans 4-t-butylcyclohexanols 44 B. Cis and trans 4-t-butylcyclohexyl acetates 47 C. Cis and trans 4-t-butylcyclohexyl methyl ethers .. 48 D. The methylcyclohexanols 51 1. Cis and trans 4-methylcyclohexanols 51 2. Cis and trans 3-methylcyclohexanols 53 3. Cis and trans 2-methylcyclohexanols 55 - iv -Page DISCUSSION 57 A. Cis and trans 4-t-butylcyclohexanols 59 A - l . The [M-H20]+ ion 61 A-2. The ions at m/e 99 and m/e 98 71 A-3. The ions at m/e 57 and m/e 56 79 A-4. The ion at m/e 123 81 A-5. The ions at m/e 80, 81, 82, and 83 82 (i) Formation of the ion at m/e 80 82 ( i i ) Formation of the ion at m/e 81 ....... 84 ( i i i ) Formation of the ion at m/e 82 85 (iv) Formation of the ion at m/e 83 93 A-6. Conclusions 94 B. Cis and trans 4-t-butylcyclohexyl acetates 100 B - l . The [M-H0Ac]+ ion and the ion at m/e 61 102 B-2. The ion at m/e 123 106 B-3. The ion at m/e 117 107 B-4. The ions at m/e 80, 81, 82, and 83 109 (i) The ion at m/e 80 1 0 9 ( i i ) The ion at m/e 81 1 1 0 ( i i i ) The ion at m/e 82 1 1 1 (iv) The ion at m/e 83 1 1 2 B-5. Conclusions H2 C. Cis aid trans 4-t-butylcyclohexyl methyl ethers ... H8 C-l. The [M-Me0H]+ i o n 1 2 0 C-2. The ion at m/e 123 125 C-3. The ions at m/e 112 and m/e 116 I 2 5 - v -Page C-4. The ions at m/e 80, 81, 82, and 83 129 (i) The ion at m/e 80 130 ( i i ) The ion at m/e 81 130 ( i i i ) The ion at m/e 82 131 (iv) The ion at m/e 83 131 C-5. The ions at m/e 71, 67, 58, and 57 132 C-6. Conclusions 134 D. The methylcyclohexanols 1 141 D-l. Cis and trans 4-methylcyclohexanols 141 D-l-1. The [M-H20]+ ion 143 D-l-2. The ion at m/e 81 148 D-l-3. The ions at m/e'57 and m/e 58 149 D-l-4. The ions at m/e 70 and m/e 71 156 D-2. Cis and trans 3-methylcyclohexanols 156 D-2-1. .The ions at m/e 71, 57 and the [M-H20]+ ion 159 D-2-2. The ion at m/e 81 162 D-3. Cis and trans 2-methylcyclohexanols 169 D-3-1. The [M-H20]+ ion 169 D-3-2. The ion at m/e 81 173 D-3-3. The ions at m/e 57 and m/e 71 173 D-3-4. The ions at m/e 68 173 D-4. Conclusions 174 E. General observations 180 CONCLUSIONS 182 REFERENCES 186 - v i -LIST OF FIGURES Figure Page 1 Interconversion of chair forms of cyclohexane 1 2 1,4-Dibsutituted cyclohexanes : 2 3 Potential energy curves for a diatomic molecule AB in i t s ground state (X) and for i t s ion AB + in i t s ground state (X) and three excited states (A), (B), (C) 14 4 Photoionisation source 39 5 Helium light source; mass spectra of trans and cis 4-t-butylcyclohexanols 95 6 Lyman a light source; mass spectra of trans and cis 4-t-butylcyclohexanols 95 7 Helium light source; mass spectra of trans and cis 4-t-butylcyclohexanol-l-d^ 96 8 Lyman a light source; mass spectra of trans and cis 4-t-butylcyclohexanol-l-d^ 96 9 Helium light source; mass spectra of trans and cis 4-t-butylcyclohexanol-2,2,6,6-d^ 97 10 Lyman a light source; mass spectra of trans and cis 4-t-butylcyclohexanol-2,2,6,6-d^ 97 11 Helium light source; mass spectra of trans and cis 4-t-butylcyclohexanol-l,2,2,6,6-d^ 98 12 Lyman a light source; mass spectra of trans and cis 4-t-butylcyclohexanol-l,2,2,6,6-d 98 - v i i -Figure Page 13 Helium light source; mass spectra of trans and cis 4-t-butylcyclohexanol-(CD 3) 3-d 9 99 14 Lyman a light source; mass spectra of trans and cis 4-t-butylcyclohexanol-(CD 3) 3-d 9 99 15 Helium light source; mass spectra of trans and cis 4-t-butylcyclohexyl acetates 113 16 Lyman a light source; mass spectra of trans and cis 4-t-butylcyclohexyl acetates 113 17 Helium light source; mass spectra of trans and cis 4-t-butylcyclohexyl acetate-l-d^ 114 18 Lyman a light source; mass spectra of trans and cis 4-t-butylcyclohexyl acetate-l-d^ 114 19 Helium light source; mass spectra of trans and cis 4-t-butylcyclohexyl acetate-2,2,6,6-d^ 115 20 Lyman a light source; mass spectra of trans and cis 4-t-butylcyclohexyl acetate-2,2,6,6-d^ 115 21 Helium light source; mass spectra of trans and cis 4-t-butylcyclohexyl acetate-l,2,2,6,6-d 5 116 22 Lyman a light source; mass spectra of trans and cis 4-t-butylcyclohexyl acetate-l,2,2,6,6-d 5 1 1 6 23 Helium light source; mass spectra of trans and cis 4-t-butylcyclohexyl acetate-(CD^)^-d^ 117 24 Lyman a light source; mass spectra of trans and cis 4-t-butylcyclohexyl acetate-(CD )„-d - v i i i -Figure Page 25 Helium light source; mass spectra of trans and cis 4-t-butylcyclohexyl methyl ethers 135 26 Lyman a light source; mass spectra of trans and cis 4-t-butylcyclohexyl methyl ethers 135 27 Helium light source; mass spectra of trans and cis 4-t-butylcyclohexyl methyl ether-l-d^ 136 28 Lyman a light source; mass spectra of trans and cis 4-t-butylcyclohexyl methyl ether-l-d^ 136 29 Helium light source; mass spectra of trans and cis 4-t-butylcyclohexyl methyl ether-2,2,6,6-d^ 137 30 Lyman a light source; mass spectra of trans and cis 4-t-butylcyclohexyl methyl ether-2,2,6,6-d^ 137 31 Helium light source; mass spectra of trans and cis 4-t-butylcyclohexyl methyl ether-l,2,2,6,6-d^ 138 32 Lyman a light source; mass spectra of trans and cis 4-t-butylcyclohexyl methyl ether-1,2 ,2,6,6-d,. 138 33 Helium light source; mass spectra of trans and cis 139 4-t-butylcyclohexyl methyl ether-(CD^)^-dg -^ Q 34 Lyman a light source; mass spectra of trans and cis 4-t-butylcyclohexyl methyl ether-(CD )„-dn 139 3 J 9 140 35 Helium light source; mass spectra of trans and cis 4-methylcyclohexanols 152 36 Ly an a light source; mass spectra of trans and cis 4-methylcyclohexanols 2_52 - ix -Figure Page 37 Helium light source; mass spectra of trans and cis 4-methylcyclohexanol-l-d^ 153 38 Lyman a light source; mass spectra of trans and cis 4-methylcyclohexanol-l-d^ 153 39 Helium light source; mass spectra of trans and cis 4-methycyclohexanol-2,2,6,6-d^ 154 40 Lyman a light source; mass spectra of trans and cis 4-methylcyclohexanol-2,2,6,6-d^ 154 41 Helium light source; mass spectra of trans and cis 4-methylcyclohexanol-l,2,2 ,6,6-d,. 155 42 Lyman a light source; mass spectra of trans and cis 4-methylcyclohexanol-l,2,2,6,6-d,. 155 43 Helium light source; mass spectra of trans and cis 3-methylcyclohexanols 164 44 Lyman a light source; mass spectra of trans and cis 3-methylcyclohexanols 164 45 Helium light source; mass spectra of trans and cis 3-methylcyclohexanol-l-d^ 165 46 Lyman a light source; mass spectra of trans and cis 3-methylcyclohexanol-l-d^ 165 47 Helium light source; mass spectra of trans and cis 3-methylcyclohexanol-2,2,6,6-d^ 166 48 Lyman a light source; mass spectra of trans and cis 3-methylcyclohexanol-2,2,6,6-d. 166 - x -Figure ' Page 49 Helium l i g h t source; mass spectra of trans and c i s 3-methylcyclohexanol-1,2,2 ,6,6-d,. 167 50 Lyman a l i g h t source; mass spectra of trans and c i s 3-methylcyclohexanol-l,2,2,6,6-d^ 167 51 Helium l i g h t source; mass spectra of trans and c i s 3-methylcyclohexanol-4,4-(CD 3)-d^ 168 52 Lyman a l i g h t source; mass spectra of trans and c i s 3-methylcyclohexanol-4,4-(CD2)-d,_ 168 53 Helium l i g h t source; mass spectra of trans and c i s 2-methylcyclohexanols 175 54 Lyman a l i g h t source; mass spectra of trans and c i s 2-methylcyclohexanols 175 55 Helium l i g h t source; mass spectra of trans and c i s 2-methylcyclohexanol-l-d^ 176 56 Lyman a l i g h t source; mass spectra of trans and c i s 2-methylcyclohexanol-l-d^ 176 57 Helium l i g h t source; mass spectra of trans and c i s 2-methylcyclohexanol-2,6,6-d^ 177 58 Lyman a l i g h t source; mass spectra of trans and c i s 2-methylcyclohexanol-2,6,6-d^ 177 59 Helium l i g h t source; mass spectra of trans and c i s 2-methylcyclohexanol-l,2,6,6-d^ 178 60 Lyman a l i g h t source; mass spectra of trans and c i s 2-methylcyclohexanol-l,2,6,6-d. 178 - xi -Figure Page 61 Possible transition state conformation resulting in loss of water by a 1,4-mechanism 65 62 A possible transition state conformation from which the hydroxyl group can readily abstract a hydrogen originating from the alkyl substituent 73 63 Chair conformations for trans and cis 4-t-butylcyclo-hexyl acetates 103 64 A possible flexible conformation from which or can be abstracted in the cis isomer 104 65 Trans 4-methylcyclohexanol 145 66 Cis 4-methylcyclohexanol 146 67 Trans and cis 3-methylcyclohexanols 157 68 Cis 3-methylcyclohexanol-4,4-(CD )-d 161 - x i i -LIST OF TABLES Table Page I [M-H.20]+/M+ ratio for cis and trans 4-t-butylcyclo-hexanols and their deuterated analogues (both light sources ) 64 II Observed m/e value for ion m* resulting from meta-stable transition 138 -> 123 in trans 4-t-butylcyclo-hexanol and for the corresponding transition in the trans deuterated analogues 67 III Observed m/e value for ion m* resulting from meta-stable transition 156 -> 99 in cis 4-t-butylcyclo-hexanol and for the corresponding transition in the cis deuterated alcohols 77 IV Observed m/e value for ion m* resulting from meta-stable transition 82 67 in both cis and trans 4-t-butylcyclohexanols and for the corresponding transition in their deuterated counterparts 87 V Observed m/e value for ion m* resulting from meta-stable transition 138 -»• 80 in both cis and trans 4-t-butylcyclohexyl acetates and for the corres-ponding transition in their deuterated analogues.... VI Observed m/e value for ion m* resulting from meta-stable transition 82 -+ 67 in both cis and trans 4-t-butylcyclohexyl acetates and for the corresponding transition in some deuterated counterparts m - x i i i -Table VII [M-MeOH]+/M+ ratio for cis and trans 4-t-butylcyclo-hexyl methyl ethers and deuterated analogues (both light sources) VIII Observed m/e value for the ion m* resulting from meta-stable transition 170 -»- 115 i n cis 4-t-butylcyclohexyl methyl ether and the corresponding transition in the deuterated analogues IX [M-t^O^/M"1" ratio for cis and trans 4-methylcyclo-hexanols and their deuterated analogues (both light sources) X Observed m/e value for the ion m* resulting from the metastable transition 114 -> 96 in cis 4-methylcyclo-hexanol and for the corresponding transition in the deuterated analogues XI Observed m/e value for the ion m* resulting from the metastable transition 96 -»- 81 in both cis and trans 4-methylcyclohexanols and for the corresponding transitions in the deuterated analogues XII Observed m/e value for the ion m* resulting from the metastable transition 96 ->- 81 in both cis and trans 3-methylcyclohexanols and for the corresponding transitions in the deuterated analogues XIII [M-l^O^/M* ratio for cis and trans 2-methylcyclo-hexanols and deuterated analogues - xiv -Table Page XIV Observed m/e value for the ion m* resulting from the metastable transition 114 ->• 96 in both cis and trans 2-methylcyclohexanols and for the corresponding transitions in the deuterated analogues 172 - XV -LIST OF SCHEMES S cheme page 1 Possible fragmentation scheme for trans 4-t-butylcyclohexanol 62 2 Possible fragmentation scheme for cis 4-t-butylcyclohexanol 63 3 Possible fragmentation scheme for both cis and trans 4-t-butylcyclohexyl acetates 101 4 Possible fragmentation scheme for trans 4-t-butyl-cyclohexyl methyl ether 122 5 Possible fragmentation scheme for cis 4-t-butylcyclo-hexyl methyl ether 123 6 Possible fragmentation scheme for both cis and trans 4-methylcyclohexanols 142 7 Possible fragmentation scheme for both cis and trans 3-methylcyclohexanols 158 8 Possible fragmentation scheme for both cis and trans 2-methylcyclohexanol 170 I - x v i -GENERAL COMMENTS AND ABBREVIATIONS USED The spectra obtained f o r a p a r t i c u l a r s e r i e s , both l a b e l l e d and unlabelled, are included at the end of the pertinent discussion section. This procedure was followed since frequent reference to these i s made throughout the preceding discussion. In the schemes " — >- " implies that the p a r t i c u l a r fragmenta-—r^ U ti o n reaction proceeds v i a a 1,4 abstraction r e s u l t i n g i n loss of water. The convention " l j j 2 " i n f e r s that the bond between C - l and C-2 i s broken. The "fishhook" notation as used i n mass spectrometry s i g n i f i e s one electron movement. A normal arrow denotes a two-electron s h i f t . The "a hydrogen" i n the systems studied re f e r s to the hydrogen on the same carbon atom as the functional group. The "8 hydrogens" r e f e r to the hydrogens on the adjacent carbons to that bearing the fun c t i o n a l group. 0 The symbol OAc refers to the acetate group (-O-C-CH^)• The symbol OMe refer s to the methoxyl group (-0-CH„). ' - x v i i -ACKNOWLEDGEMENTS I wish to express my g r a t i t u d e to both Dr. C.E. B r i o n and to Dr. L.D. H a l l f o r suggesting the problem and f o r a l l the help and guidance r e c e i v e d during the course of t h i s i n v e s t i g a t i o n . S p e c i a l thanks are due to Dr. R.E. Pincock and to Mr. L . J . Muenster f o r the generous use of t h e i r equipment and to Mr. G. Gunn f o r h i s ass i s t a n c e i n the operation of the mass spectrometer. I am g r a t e f u l to my husband f o r h i s patience and understanding and a l s o f o r h i s help during the p r e p a r a t i o n of t h i s t h e s i s . F i n a n c i a l a s s i s t a n c e i n the form of a Bursary and Sch o l a r s h i p from the N a t i o n a l Research C o u n c i l (Ottawa) i s g r a t e f u l l y acknowledged. - 1 -INTRODUCTION During the past few years an increasing amount of interest has developed in the study of the influence of stereochemistry on mass spectral fragmentation reactions (1,2,3,4). It has generally been observed that mass spectra of stereoisomers are in many cases qualitatively and even quantitatively very similar (5,6,7). The majority of these studies have been carried out using a conventional electron impact ionisation source, larger differences being observed between isomers at lower electron energies. It has been known for some time that the cyclohexane ring is free of angle strain and can exist in two distinct conformations, chair inversion occurring rapidly through the flexible form intermediate. In this process of inversion a l l axial bonds become equatorial and vice versa (8), (Fig. 1). Fig. 1 Interconversion of chair forms of cyclohexane. - 2 -In disubstituted eyclohexanes i t is now possible to have two stereoisomers cis and trans, which have identical structures but differ only in the spatial arrangement of the component atoms. Each of these isomers can exist in two distinct chair conformations besides a l l other intermediate forms. Fig. 2 shows the case for 1,4-substituted eyclohexanes. ^ trans CIS (X smaller group than Y) Fig. 2 1,4-Disubstituted eyclohexanes. Similar conformations can be drawn for 1,2- and 1,3-substituted eyclohexanes;. In the case of 4 (or 3) tertiary butyl substituted eyclohexanes the reluctance of the large tertiary butyl group to occupy the axial position indicates that the equilibrium i s largely in favour of the conformer with the tertiary butyl group in the equatorial position (9). Further in the example quoted above i t has been shown from thermodynamic data (10) that the cis isomer has more internal energy associated with i t than the trans isomer. This excess energy is a result of interactions due to the proximity of - 3 -certain atoms or substituents. I n i t i a l l y , i t was the above mentioned thermodynamic property that was used to explain differences in the mass spectra of stereoisomeric hydrpcarbons (5,11,14). Work done by Natalis and co-workers (7,5) on stereoisomeric pairs of d i - and trisubstituted cycloalkanes indicated that the trans isomers always gave the more intense parent peak. This observation was rationalized in terms of the greater thermodynamic st a b i l i t y of the trans isomer. However, the trans isomer is not always the more stable, for example, in 1,3-disubstituted cyclohexanes. Meyerson (3) has suggested that for stereoisomeric hydrocarbons, fragmentation reactions do not involve rigorous geometric requirements but depend on the attainment of a transition state defined in terms of a minimum energy content. His conclusions are based on the observation that although the ionisation potentials obtained for some pairs of stereoisomers (7,5) are almost identical, the appearance potential of certain fragment ions show a difference which is equal in magnitude (within experimental error) but opposite in sign to the difference between the heats of formation of the stereoisomers (15). Thus, the absolute energy from which decomposition occurs, arrived at by summing the heat of formation of the molecule and the appearance potential of the fragment ion, are the same for cis and trans isomers. Molecules which contain a heteroatom probably fragment along paths directed by the heteroatom containing functional group (34), therefore, fragmentation mechanisms would be expected to be different from those of hydrocarbons. Epimeric alcohols have been studied - 4 -previously by Biemann (13,16,17) who found that the more stable (less crowded) epimer consistently gave the more intense parent peak, whereas the less stable isomer (more crowded) gave the more intense peak corresponding to loss of water. However, data from other laboratories (18,19,20) which were subsequently reported are inconsistent with this correlation thus suggesting that, perhaps, more subtle effects are involved. Since the fragmentation sequence followed depends on the amount of energy transmitted to the molecule by the bombarding particle; a reduction in the i n i t i a l energy content of the molecular ion would lead to simpler decomposition sequences resulting in ions formed mainly by primary and secondary processes. The difference ( i f any) present in the mass spectra of stereoisomers can thus be accentuated. Furthermore, as Meyerson and Weitkamp (3) have pointed out, the effect of reducing the i n i t i a l energy content of the molecular ion can be expected to: (a) minimise epimerization of the molecular ion, (b) reduce contributions of processes stemming from conformations other than those of the lowest energy and, (c) limit further decomposition of the primary products which are diagnostically the most useful ones. In a conventional electron impact source thermal effects may be contributing significantly to the spectrum observed (27). This may be due in part to pyrolysis on the hot filament (1800°C) as well as decomposition on the hot walls of the ion source (ranges between 70-250°C). In addition to thermal decomposition the temperature may also contribute to the fragmentation of a molecule by imparting additional - 5 -thermal energy through collisions with the hot walls prior to ionization, although the latter effect w i l l be small. The use of lower ionising voltages and lower temperatures results in molecular ions having less energy content compared to those obtained with a conventional electron impact source (70 eV electrons). However, there are problems associated with this method. Not only ' is there a Maxwellian thermal spread of electron energies but also space charge which can modify the nominal energy. This i s specially serious at low electron energies and can lead to lack of reproducibility in the mass spectra due to the d i f f i c u l t y of obtaining the same absolute electron energy. Furthermore, the sensitivity is several orders lower when using low energy electrons for ionisation (16). With the use of a photoionisation source, which completely disposes of hot filaments since ionisation is now affected by photons of sufficient energy, the ion chamber can be kept at any desired tempera-ture. Furthermore, the energy of the ionising radiation is also closely defined. The f i r s t report of the use of a beam of photons to produce ionisation appeared in 1929 (21). Potassium vapour was irradiated with photons from an iron arc, the light passing through quartz windows into the ion source of a simple magnetic mass analyser. In 1932, Terenin and Popov (22) using a more refined experimental setup, studied the photoionisation of thallium halides. However, due to technical d i f f i c u l t i e s associated with the source no serious development took place until twenty-four years later. With the application of improved vacuum techniques Lossing and Tanaka (23) used the resonance - 6 -line emitted by a discharge through Krypton as the ionising radiation coupled with the use of LiF as window material. Under these conditions ionising energies in excess of 10 eV were not available. Thus molecules with ionisation potentials greater than 10 eV could not be studied. The use of very efficient differential pumping subsequently allowed the removal of the window and the result was that no restriction was placed on the energy of the transmitted photon beam available. Many workers (24,25) active in the f i e l d have designed suitable photoionisation sources primarily for the study of threshold ionisation phenomena. Grating monochromaters are used to vary the wavelength in a precise manner. However, the resulting photon fluxes are very low and generally not suitable as the ionising source for an analytical mass spectrometer where a high ionising flux at a single energy is required. •' Line radiation which is produced by electronic transitions between different energy levels in neutral atoms and molecules and in ions is generally suitable for mass spectrometric studies. The use of undispersed radiation eliminates the use of a monochromator i f the radiation is essentially monochromatic. Photoionisation sources specifically designed for use with commercial analytical mass • spectrometers have been described by Beynon et a l . (26) and Brion'(27) using either d.c. discharge or microwaves to produce typically the o o 584 A (21.22 eV) helium resonance line or the 1215 A (10.19 eV) hydrogen Lyman a line. Due to the nature of the photoionisation threshold law (28) these light sources provide sufficient energy to give satisfactory mass spectra. - 7 -The present study involves the use of photoionisation to examine the spectra of cis and trans 4-tertiarybutylcyclohexanol and to further elucidate by the use of deuterated derivatives the fragmenta-tion mechanisms involved. The study was further extended to include cis and trans isomers of 4-tertiarybutylcyclohexyl methyl ether and 4-tertiarybutylcyclohexyl acetate and their deuterated counterparts. An attempt was also made to understand the fragmentation behaviour of cis and trans 2, 3, and 4 methyl substituted cyclohexanols in terms of their spatial configuration. - 8 -THEORETICAL (a) Mass Spectrometer A variety of spectrometers have been designed and constructed and many reviews have appeared on the subject (29,30). The basic mass spectral equations are as follows: A positive ion of mass m and charge e that has been accelerated by a voltage V w i l l acquire kinetic energy eV. Normally the accelerating potential is large compared to the i n i t i a l energy distribution and, therefore, one can assume that a l l ions entering the magnetic f i e l d of strength H w i l l have a discrete velocity v after acceleration such that 1 2 eV = -j • mv (1) In the magnetic f i e l d the ion w i l l experience a centripetal force Hev. The ions w i l l , therefore, be deflected into a circular orbit resulting from the balancing of centrifugal and centripetal forces 2 where R = radius of curvature of the ion beam. - 9 -Combining (1) and (2) eH indicating that an ion with a specific m/e value is deflected with a certain value of R. To obtain better resolution, the energy band-width of the ion beam before i t enters the magnetic f i e l d can be reduced by allowing the ions to pass through an electrostatic analyser. The ion experiences a force eE and the result is a circular path of radius r given by 2 eE = Hv_ mv2 2V or r = = r=r-eE E A radial electric f i e l d , therefore, deflects ions according to their kinetic energy and allows only ions with a given value of kinetic energy to pass to the magnetic analyser. Thus, instruments using both electrostatic and magnetic analysers achieve both velocity and direction focussing. (b) Metastable Ions Some of the ions formed in the ionisation chamber are sufficiently stable so that they can be withdrawn from the chamber. However, their half l i f e is of the order of a microsecond and most of them w i l l dissociate on their way to the collector. These ions normally are - 10 -observed as small diffuse peaks in the spectrum appearing at non integral mass numbers. In a sector type instrument they arise as follows. Suppose an ion of mass m^  f a l l s through a potential difference of before decomposing into an ion of mass n^. This new ion of mass m^  traverses the remainder of the accelerating voltage (V-V^) and enters the f i e l d free region leading to the magnetic analyser. The mass m w i l l enter the magnetic analyser with velocity v given by 1 2 2 m 2 V m,. eV 1 + eCV-V^ The ion w i l l traverse the magnetic f i e l d of strength H with radius of curvature R given by R = 2V 1/2 _H e m9 (m -m )(V-V ) m l m 2 V 1/2 This is also the radius of curvature with which normal ions of mass m* traverses the magnetic f i e l d where 1/2 R = 2V H2e m* .1/2 Therefore, the metastable transition gives rise to a peak at a position corresponding to m* where m„ 1 + (m1-m2)(V-V1) m2V - 11 -In general dissociation may occur anywhere between the source and collector, however, decomposing ions most li k e l y to be recorded are those that undergo the transition in the vi c i n i t y of the entrance s l i t of the spectrometer at the end of the accelerating region so that for the observed peak 2 (c) Photoionisation Photoionisation can occur by the interaction of a photon of sufficiently high energy with a molecule. Four major processes resulting from photoionisation are as follows: (1) Simple ionisation: AB + hv •+ AB + + e where h = Planck's constant and v = frequency of the radiation The minimum energy necessary for this process i s called the adiabatic ionisation potential of AB. (2) Autoionisation: AB + hv -> AB** ->• AB + + e~ where AB represents the AB molecule excited to a discrete state above i t s ionisation potential. - 12 -Removal of an electron from a molecule by a method which does not involve a transition directly into the continuum i s known as autoionisation, i.e. ionisation takes place in two stages and involves excitation of the neutral species to a discrete state above i t s ionisation potential followed by decay via a radiationless transition and loss of the electron. (3) Dissociative ionisation: AB + hv -> AB + + e where is the kinetic energy I I of fragmentation A + + B + E, k The minimum photon energy necessary for this process is called the appearance potential of A +. (4) Ion pair formation: * + AB + hv -> AB -> A + B + E, k (d) Formation of ions Ionisation by photons or electrons of sufficient energy w i l l result in the population of a variety of molecular ion states. For photoionisation i t has been shown both theoretically (28) and experimentally (31) that the probability for ionisation rises sharply at the threshold and tends to assume a constant value decreasing somewhat at higher ionising energies. This implies that the maximum probability for the production of ions in a particular state w i l l occur - 13 -at or near the threshold of that process. However, in the case of electron impact, i t has been shown from experimental results that the cross section i s zero at the threshold and increases approximately linearly as a function of the excess energy (32). Therefore, significant populations of a l l accessible ion states w i l l be obtained with photoionisation even at low energies. The situation w i l l obviously differ markedly in the case of electron impact. Consequently differences would be expected in mass spectra produced by photo-ionisation and electron impact especially at low ionising energies. In addition, autoionisation (which i s a resonant process for photons) would in general not contribute to the process of photoionisation as used in this work. Non-resonant electron impact induced auto-ionising processes may make a very significant contribution to the total ionisation. The process of ionisation and dissociation of a diatomic molecule can be well understood in terms of two dimensional potential curves as a vertical transition from the potential curve of the ground state to that of the fi n a l state. Figure 3 shows the potential energy curves for a diatomic molecule AB in i t s ground state (X) and for i t s ion AB in i t s ground state (X) and three excited states(A) (B) (C). A l l transitions originate from the zeroth vibrational level of the ground electronic state. According to the Franck-Condon principle an electronic transition occurs in a time much shorter than that required for a single molecular vibration. The maximum probability for the transition occurs at the centre of the Franck-Condon region (marked by shading). - 14 -r Fig. 3. Potential energy curves for a diatomic molecule AB in i t s ground state (X) and for i t s ion AB in i t s ground state (X) and three a. % >v, excited states (A) (B) (C). (schematic) - 15 -Excitation to the electronic state (X) where the equilibrium internuclear distance r g i s the same or very nearly the same as that in the ground state (X) requires by the Franck-Condon principle that the most probable transition is to the v'=0 level of the state (X). These transitions are termed adiabatic transitions. Excitation from the state (X) to the state (A) corresponds to the case where r g is slightly less than that in the ground state. In this case the maximum transition probability occurs for a transition to the y'=l level. Transitions w i l l occur to other levels within the Franck-Condon region. A transition from the state (X) to the state (B) where there i s a large change in r g result in transitions either to vibrational levels 4-below the dissociation limit in which case an excited AB ion is formed or to the continuum where the ion fragments into A + and B, in which case the excess energy w i l l be distributed between the ion and the neutral fragment. A transition from state (X) to the state (C) which i s a repulsive state w i l l result in dissociation of the ion. The transition from the ground state (X) to the excited ionic state (A) also indicates how some of the excess vibrational energy in the ion is acquired. Another source of vibrational energy i n an ion arises from the process of interstate crossing which occurs whenever electronic ion states cross at some point and radiationless transitions can take place from one state to another converting electronic energy into vibrational energy. - 16 -For polyatomic molecules the picture i s not so simple. The two dimensional potential energy curves must be replaced by potential surfaces and because of the many different vibrational modes and partitioning of energy there is a greater likelihood that inter-state crossing can occur. This cascade process does not necessarily lead to a ground state ion since interstate crossing w i l l cease where there is no potential surface crossing and, thus an electronically excited ion may be formed. It is also possible that some of these states may be reactive and therefore rearrangement or dissociation may occur. The ionisation process therefore leads to molecular ions having a range of excess energies and since each ion has i t s own excess energy i t w i l l possess i t s own half l i f e for decomposition and w i l l decompose at i t s own rate, along different paths possibly from different electronic states. (e) Quasi equilibrium theory Rosenstock, Wallenstein, Wahrhaftig, Eyring and Krauss (33) by applying s t a t i s t i c a l concepts have developed a theory of mass spectra of large unsymmetrical polyatomic molecules. This theory attempts to explain in a mathematical form the decomposition of ions in terms of excess vibrational energy. The rate of dissociation of the ion is determined by the probability of the distributed energy becoming con-centrated in a particular manner, giving rise to activated complexes which in turn yield the dissociated products. In terms of the simplified theory the rate constant k for unimolecular ion decomposition is given by the expression - 17 -r E Eo ,N-1 k= v[ — ] where E i s the excess vibrational energy in the ion E^ the activation energy for the process v i s the frequency factor N is the effective number of oscillators in the ion. Some success has been made for the calculation of spectra of simple molecules but not for molecules containing functional groups. The theory, unfortunately, requires the answers before a mass spectrum can be calculated, that i s , i t is necessary to know the structures of the decomposing ions and also how they decompose. (f) Qualitative theories of mass spectra: "Mechanistic Approach" The "mechanistic approach" is concerned with rationalisations of how and why certain fragmentations occur. Budzikiewicz et a l . (34) have pointed out that the term mechanism is a euphemism in mass spectrometry since none of the charged species formed i n the mass spectrometer are isolated nor are their structures determined in the classical sense. Some of the methods used for inferring the structures of ions are isotopic labelling, metastable studies and high resolution. Using supporting evidence from concepts of physical organic chemistry such as resonance, polarizability, inductive effects, steric effects, together with the information obtained from the mass spectrometric studies, attempts are made to formulate mechanisms which could give rise to the fragment ions. - 18 -A generalisation which has been proposed for mass spectral mechanisms involves the location of the positive charge at favoured sites in the ion (34) instead of visualisation of the positive charge as being distributed over the ion structure. This positive charge was then looked upon as being able to trigger particular decomposition reactions. Recently (35) this concept has been extended to consider the reactivity of the unpaired electron as well as that of the positive charge. In many cases both the charge and the unpaired electron are located at the same site but decompositions of cyclic molecules and rearrangement ions usually involve ion species in which these sites have been separated. Furthermore, i t appears that the positive charge and the unpaired electron exhibit quite different reactivities (35) although further work is necessary to clarify these differences. The main limitation of this approach is that i t assumes that the molecular ion formed is similar in structure to the neutral molecule, the only difference being that the ion has one electron less. The electron that i s lost in the ionisation process is considered to be from the highest occupied molecular orbital, i.e. one that is most loosely bound. This usually happens to be an electron from one of the non-bonding orbitals (n) on the heteroatom in molecules containing such an atom. In hydrocarbons the removal of a 7r-electron is favoured in the absence of which a a-electron i s lost. The relative ease of removing an electron appears to be in the order n > IT > a (35). However, there have been examples quoted in the literature (85) where TT , a and non-bonding energy levels have been shown not to follow the general order expected, e.g. in molecules containing both an aromatic - 19 -group and a heteroatom such as aniline, and electron from a IT bond is lost most easily. This would thus lead to d i f f i c u l t i e s . i n localising the charge at a specific site in the molecule in the absence of any other information. Furthermore, i t is also possible that ionisation from any energy level may take place resulting in excited ions. These ions may convert electronic energy into vibrational energy by radiationless transitions but this would not necessarily lead to a ground state ion. An electronically excited ion may be formed and fragmentation may occur from this state. Such processes would also lead to d i f f i c u l t i e s in attempts to localise the charge and radical at specific sites. It has been observed that many compounds when examined in a mass spectrometer produce fragments whose origin cannot be described by simple cleavage of bonds in the parent ion. These are normally attributed to atomic rearrangements during the fragmentation process. These ions formed by rearrangement reactions have been found to increase in relat-ive abundance when low ionising voltages were utili s e d (56). This observation has been explained in terms of the low activation energy required for these processes compared to direct bond cleavage reactions. Furthermore, Field and Franklin (84) have pointed out that small activation energies permit the atoms and bonds in the ion to be extremely mobile. Often rearrangement reactions result i n the formation of a small stable neutral molecule, e.g. CO, H^ O, CH^ OH. It has been suggested (87) that a lower transition state energy results from a combined effect of bond formation and bond breaking. The sta b i l i t y of the neutral product formed may be considered to provide the driving force for the reaction. - 20 -The s t a b i l i t y of the ionic product formed may also play an important role in the fragmentation reactions taking place in the spectrometer. In general ions (not in the excited state) with an even number of electrons are more stable and may be further stabilized due to the following structural factors (59). + + 1. electron sharing CH20H <—> CH2=0H + + 2. resonance effect CH2~CH=CH2 CH2=CH-CH2 3. inductive effect. This approach considering the sta b i l i t y of the neutral and ionic product formed was i n i t i a l l y u t i l i s e d by Biemann (6) in his discussion of mass spectra. Although the concept of charge and radical localisation i s an over-simplification,it has proved useful(together with concepts of ground state chemistry)in interpreting and predicting mass spectral data especially of large organic molecules. - 21 -EXPERIMENTAL Part A: Synthesis and Purification of Compounds The following techniques and experimental methods were used where necessary in the preparation of the compounds studied. (1) A l l nuclear magnetic resonance spectra were run on the Varian Associates HA 100 n.m.r. spectrometer or the Varian Associates T-60 n . m , r . spectrometer using tetramethylsilane as internal standard and chloroform as solvent unless other wise specified. (2) Melting points were taken on a Fisher-Johns melting point apparatus. A l l corrected melting points are reported. (3) Separation of the isomers was carried out on the Aerograph Autoprep Model A-700 Gas Liquid Chromatograph using helium as carrier gas. The following columns were used. For the alcohols a 10' x 3/8" 30% diglycerol on chromosorb W column. For the acetates and methyl ethers a 10' x 3/8" 20% Carbowax 20 m on chromosorb W column. The solid samples were collected using the collection assembly commercially available with the instrument. The compounds were removed from the collection bottles by scraping out the crystals which formed quite readily in the neck of the bottles. The liquid samples were collected directly into glass capillary melting point tubes. The exit tube leading out from the machine was adapted for this purpose by soldering - 22 -a copper tube (the same length as the original exit tube) , to a short syringe needle. The tube was kept at the collector temp.erature by means of a small heater through which i t was inserted. The capillary tube, when collecting a sample, was cooled with a jet of cold air. The sample tube was sealed to prevent loss or contamination. The compounds studied during the course of this investigation were synthesised and/or purified as follows: (a) Cis and trans-4-t-butyloyatohexanot Commercially available 4-tertiarybutylcyclohexanol, (Aldrich Chemicals), a mixture of cis and trans alcohols, was separated and collected using Gas-Liquid Partition Chromatography under the following conditions: carrier gas (He) flow rate 60 ml/min collector temperature 140°C oven temperature 95°C detector temperature 240°C injector temperature 210°C The retention times were as follows: (i) cis-4-t-butylcyclohexanol 52.5 min ( i i ) trans-4-t-butylcyclohexanol 89 min Both isomers were white crystals of high v o l a t i l i t y cis-4-t-butylcyclohexanol melting point 82°C [ l i t . m.p. 81-82°C(9)] trans-4-t-butylcyclohexanol melting point 79-80°C [ l i t . m.p. 80.5-81°C (9)] - 23 -The purity of the samples collected was checked by n.m.r. The difference in nature and position of the proton absorption band (36) was used to differentiate between the two isomers as well as to evaluate purity. For the trans isomer the proton appears at 6.5 T and being axial couples more strongly with the other hydrogens of the ring resulting in a broad absorption peak. For the cis isomer the proton appears at 5.96 x with a much narrower peak. (b) Preparation of 4-t-butylcyclohexanone-232}6,63d^ The deuteration of positions two and six of the cyclohexane ring was done by the method of Greig et a l . (37). Five grams of 4-t-butylcyclohexanone (Aldrich Chemicals) in 20 ml of dry dioxane was added to 20 ml B^O (deuterium oxide) in which a small piece of Na was dissolved. The solution was stirred for f i f t y hours, after which i t was extracted with three 25 ml portions of diethyl ether, washed with water and dried over sodium sulphate. After removal of drying agent and ether, white needle-like crystals resulted (yield 98%). The n.m.r. spectrum of the compound using the tertiary butyl group as a b u i l t - i n standard indicated approximately 80% deuteration. The ketone was recycled twice more and almost complete deuteration was achieved. The yield was 90% with the crystals melting at 45-48°C ( l i t . m.p. 47.5-48.5°C (9)). - 24 -(c) Preparation of cis and trans 4-t-butylcyclohexanol-l-d^ One gram of 4-t-butylcyclohexanone in dry ethyl ether (10 ml) was added to a stirred suspension of 0.2 g of lithium aluminum deutride in ether (20 ml). After the dropwise addition the reaction was refluxed for two hours and the excess LiAlD^ decomposed with wet ethyl ether. The ether layer was separated and the water layer extracted with two portions of 15 ml ethyl ether. The combined extracts were dried over sodium sulphate. After removal of the solvent white crystals were obtained (yield 90%, melting point 60-70°C). N.m.r. indicated the absence of the proton absorption indicating replacement of the proton by deuterium. The crystals were dissolved in acetone and separated and collected as described under (a). (d) Preparation of cis and trans 4-t-butylcyclohexanol-2}2J6,6-d^ The same procedure as under (c) was followed reacting one gram of 4-t-butylcyclohexanone-2,2,6,6-d^ with lithium aluminum hydride. Separation and collection was made as under (a). (e) Preparation of cis and trans 4-t-butylcyclohexanol-l32}236i6-d^ As under (d) replacing LiAlH^ with LiAlD^. The mixture was separated out as under (a). - 25 -(f) Preparation of cis and trans 4-t-butylcyclohexanol-(CD^)^-d (i) C(CD 3) 3 The method ut i l i s e d for the preparation of tertiarybutyl benzene was adapted from reference (38). To a stirred mixture of 7.5 ml of benzene (dried over sodium) and 2 g of aluminum chloride (anhydrous) 3 ml of tertiarybutyl chloride-d^ (Merck, Sharp and Dohme (99%)) was added slowly. The mixture was maintained at 0°C using an ice-water bath. Stirring was continued for two hours, after which 7 g of ice and 6 ml of water was slowly added. The mixture was steam d i s t i l l e d and the hydrocarbon layer separated. The water layer was extracted with three 10-ml portions of diethyl ether and dried over magnesium sulphate. The solvent and drying agent was removed and a n.m.r. spectrum obtained. Only resonances due to the aromatic protons were observed. No resonances due to the tertiarybutyl protons were observed. The infrared spectrum obtained was similar to that of tertiarybutyl benzene with the shift observable for C-D stretch at ^ 2093 cm - 26 -( i i ) SCLNa The process used was adapted from reference (38). To 1 g of tertiarybutyl benzene-d^, 0.6 ml of concentrated sulphuric acid was added. The mixture was stirred at 0°C for one hour. Four ml of water was added, followed by 0.5 g of sodium bicarbonate. The solution was boiled and saturated with sodium chloride. On cooling, flaky white crystals separated out. Filtered and recrystallized from water saturated with sodium chloride. Filtered and dried in the oven overnight (yield 0.45 g). The sodium salt with the tertiary butyl group para to i t w i l l only be formed. No ortho equivalent w i l l be formed due to steric effects (40). ( i i i ) Procedure was adapted from reference (38) - 27 -In a nickel crucible the salt obtained from the preceding preparation was placed together with 1.2 g of potassium hydroxide and two drops of water. The crucible was heated so that the mixture just melted. The fusion was continued for another few minutes with sti r r i n g . The mixture was cooled and 2 ml of water was added. Heat was applied to dissolve the mass. The solution was then poured into a beaker and 50% sulphuric acid was added very cautiously u n t i l acid to pH paper. This was extracted with three 10-ml portions of diethyl ether, dried over sodium sulphate and the solvent removed. A white solid formed, melting point 95-98°C [ l i t . m.p. 99°C (38)]. The n.m.r. spectrum obtained showed a small absorption due to the tertiary butyl group. Approximately 91% of the deuteriums were retained. Procedure adapted from reference (39). One-eighth teaspoon of Raney nickel catalyst (commercially available Grace Davidson Chem. No. 28) was placed in a hydrogenation bottle and washed with isopropyl alcohol. The phenol obtained from ( i i i ) was added together with 10 ml of isopropyl chloride. The hydrogenation 2 was carried out at a pressure of 60 lbs/in and at 80°C for a period of five hours. After cooling, the catalyst was removed and washed with (iv) OH OH - 28 -CHCly The f i l t r a t e was washed with 5% HC1, water and sodium bicarbonate and fi n a l l y with water. Dried over sodium sulphate. On removal of solvent, white crystals obtained, m.p. 60-70.5°C [ l i t . m.p. 62.5-70°C for 29.4:70.6 cis:trans mixture (9)]. The n.m.r. spectrum indicated that the saturated alcohol was formed. Approximately 90% fully deuterated material was estimated from n.m.r. integrals. The mixture of alcohols was separated out as under (a). (f)' The same procedure was repeated for steps ( i ) - ( i v ) . However, in step ( i i ) the mixture was le f t s t i r r i n g for a longer period (two hours) in order to increase the yield. This appeared to result in a larger loss of deuterium. Exchange of protons in an alkyl aromatic molecule is known to occur under both acidic and basic conditions. The aromatic protons and the hydrogens on the alkyl group can be exchanged depending on the conditions ut i l i s e d (41). Cg) Preparation of cis and trans 4-t-butylcyclohexyl acetate To 0.4 g of a mixture of 4-t-butylcyclohexanols 10 ml of pyridine and 10 ml of acetic anhydride was added at 0°C. The mixture was l e f t standing overnight and the unreacted acetic anhydride decomposed with an ice-water mixture. The organic material was extracted with chloroform and the extracts washed with 0.2 N H„S0., 5% NaHC0„ and water and 2 4 3 dried over sodium sulphate. After removal of solvent a yellow sweet-smelling o i l resulted (yield 80%). Identified from n.m.r. spectrum (86). - 29 -proton of the trans acetate at 5.45 T; OAC group 8.08 T proton of the cis acetate at 5.03 T; OAC group 8.0 T. The mixture was separated and collected on the gas-liquid chromatography machine using a 20% Carbowax 20 M column under the following conditions: carrier gas flow rate (He) oven temperature injector temperature collector temperature detector temperature 75 ml/min 165°C 210°C 140°C 240°C Retention times cis acetate trans acetate 35 min 46 min The order of elution i s as reported by Karger et a l . (42) using the same type of column. The peak corresponding to the trans isomer was further verified by preparing a sample of pure trans 4-t-butyl-cyclohexyl acetate from pure trans 4-t-butylcyclohexanol. (h) Preparation of cis and trans 4-t-butylcyclohexyl acetate-l-d^ The same procedure as under (g) was followed by reacting 0.2 g of 4-t-butylcyclohexanol-1-d . (i) Preparation of cis and trans 4-t-butylcyclohexyl acetate-2,236i6-d^ The same procedure as under (g) was followed by reacting 0.2 g of 4-t-butylcyclohexanol-2,2,6,6-d^. - 30 -(j) Preparation of cis and trans 4-t-butylcyclohexyl acetate-I,2,2, 636-d The same procedure as under (g) was followed by reacting 0.2 g of 4-t-butylcyclohexanol-l, 2,2,6,6-d. (k) Preparation of cis and trans 4-t-butylcyclohexyl acetate-(CD )-dQ C O i? The same procedure as under (g) was followed using 0.02 g of deuterated alcohol synthesised as under ( f ) . (1) Preparation of cis and trans 4-t-butylcyclohexyl methyl ether To 1 g of sodium (small pieces) i n 50 ml dry diethyl ether was added 5 g of a commercially available mixture of 4-t-butylcyclohexanol in 25 ml diethyl ether. The mixture was stirred and refluxed for 24 hours. Methyl iodide (50 g) was then added and the mixture l e f t stirring for 24 hours. Unreacted sodium was decomposed with wet ethyl ether and the mixture extracted with ether. The solution was dried over Na„S0, and the solvent removed. I 4 The mixture was separated and collected by gas liquid chromatography using a Carbowax 20 M column. The conditions were as follows: carrier gas (He) flow rate 75 ml/min injector temperature 210°C column (oven) temperature 160°C detector temperature 240°C collector temperature 140°C - 31 -Retention times cis 11 min trans 16 min The liquid obtained had approximately 30% of unreacted alcohol which had the following retention times under the conditions stated above. cis 4-t-butylcyclohexanol 40 min trans 4-t-butylcyclohexanol 48 min The ethers could be separated and collected in a pure form. A sufficient amount for an n.m.r. spectrum was collected of the larger ether peak which corresponded to the trans isomer (86). The 20 refractive index n^ 1.4495 agreed with that quoted in the literature 20 for the trans isomer (n^ 1.4497) (43). (m) Preparation of cis and trans 4-t-butylcyclohexyl methyl ether-l-d^, cis and trans 4-t-butylcyclohexyl methyl ether-2i2,6i6-d^, cis and trans 4-t-butylcyclohexyl methyl ether-l,2,2i6i6-d^ The same procedure as under (1) was followed using the 0.5 g of the corresponding alcohols. (n) Preparation of cis and trans 4-t-butylcyclohexyl methyl ether-(CD^) -cZ (i) The same procedure as under (1) was followed using 0.05 g of the mixture of alcohols synthesised as under (f ) . In this case, only sufficient quantities of the trans 4-t-butylcyclohexyl methyl ether-d^ was obtained. ( i i ) The product obtained as under ( f ) 1 was reacted as under (1) and sufficient quantities of both cis and trans isomers was obtained. (o) Cis and trans 4-methylcyclohexanol Commercially available 4-methylcyclohexanol (Aldrich Chemicals), a mixturecf cis and trans isomers, was separated and collected using gas-liquid chromatography. The column used was a 10' x 3/8" 30% diglycerol on Chromosorb W. The following conditions were used: carrier gas flow rate injector temperature detector temperature collector temperature 60 ml/min 210°C 240°C 140°C Retention times cis 4-methylcyclohexanol trans 4-methylcyclohexanol 30 min 43.5 min (p) Oxidation of 4-methylcyclohexanol The oxidation was carried out according to the method of Parikh and Jones (44). In a 500 ml erlenmeyer 5 g of a mixture of cis and trans 4-methyl-cyclohexanols, 150 mg of Ru02, 200 ml of carbon tetrachloride, 1.6 g of NaHCO^ and 30 ml of water was added. Nine grams of sodium periodate was dissolved in 150 ml d i s t i l l e d water. The contents of the erlenmeyer was stirred vigorously while the periodate solution - 33 -was added dropwise. After the addition, the bottom layer was separated and the water layer extracted with chloroform* The combined extracts were dried over Na„S0,. On removal of the solvent, 2 4 a yellow syrup remained (yield 80%). I.r. spectroscopy on the liquid (between salt plates) showed no presence of the stretching frequency for the hydroxyl group. The appearance of the carbonyl stretching frequency at 1725 cm ^ indicated the formation of the ketone. (q) Preparation of 4-methylcyclohexanone-23 23636-d^ The procedure followed is as outlined under (b) using 3 g of 4-methylcyclohexanone. The ketone was recycled three times before a sufficient amount of deuterium was incorporated. (r) Preparation of cis and trans 4-methylcyclohexanol-l-d^3 cis and trans 4-methylcyclohexanol-2323636-d^3 cis and trans 4-methyl-cyclohexanol-l3 23 23 63 6 - d r o The procedure followed is as under (c) using 1 g of the appropriate ketone and hydride. The products obtained were purified and collected as under (o). (s) Preparation of Z-methylcyctohexanone-2323636-d^ The same procedure was followed as outlined under (b) using 5 g of commercially available 3-methylcyclohexanone (Aldrich Chemicals). The ketone was recycled three times before a sufficient amount of deuteration was achieved. - 34 -(t) Preparation of cis and trans 3-methylcyclohexanol These alcohols were prepared as under (c) using 1 g of 3-methyl-cyclohexanone and lithium aluminum hydride. The products obtained were separated using gas-liquid chromatography. The same conditions as under (o) prevailed. Retention times trans 3-methylcyclohexanol 25 min cis 3-methylcyclohexanol 34 min The retention times agree with the product ratio expected from LiAlH^ reduction (.10). (u) Preparation of cis and trans 3-methylcyclohexanol-232s636-d^3 cis and trans 3-methylcyclohexanol-l-d^, cis and trans 3-methyl-cyclohexanol- ly 2, 2, 6y 6-dr The same procedure as under (c) was followed using the appropriate ketone and hydride. The alcohols were purified and separated as under (t). (v) Preparation of cis and trans 3-methylcyclohexanol-434-CD^-d^ The method used in the synthesis was obtained from reference (45) ( i ) C D . - 35 -A small piece of sodium (0.2 g) was dissolved in 20 ml MeOD and 0.5 g of 3-methyl-2-cyclohexen-l-one added to i t . The solution was heated to boiling after which 15 ml of D^O was added and the solution refluxed for 36 hours. After cooling, 10 ml of D,>0 was added and the mixture was extracted with ether. The extracts were dried over Na„S0, and the solvent 2 4 removed. A yellow syrup remained, ( i i ) 0 0 The syrup obtained from (i) was hydrogenated at atmospheric pressure using ethyl acetate as solvent and Pd/C as catalyst (50 mg). After uptake of hydrogen ceased the catalyst was f i l t e r e d and the solvent removed on a rotary evaporator. The remaining syrup was analysed by gas-liquid chromatography using 10T x 3/8" diglycerol (30%) column. The retention time obtained for the major peak corresponded to that obtained for 3-methylcyclohexanone under the same conditions ( i i i ) 0 0 - 36 -The crude ketone obtained from preparation (v)(ii) was dissolved in 5 ml methanol and 1 ml of 2.5 N NaOH was added and the solution refluxed for one hour. After cooling, the solution was extracted with ether and dried over sodium sulphate. After removal of solvent a yellow syrup remained. Civ) The crude ketone obtained from ( i i i ) was dissolved in 5 ml dry ethyl ether and added dropwise to 0.1 g of LiAlH^ in 10 ml dry ethyl ether. After refluxing for one hour the mixture worked up as under (c). The yellow liquid obtained was analysed by gas-liquid chromatography, the same conditions as under (t). Two major peaks corresponding to the cis and trans isomers were observed together with a small impurity peak. The purified alcohols were collected as under (t). For extent of deuterium incorporation and positions of deuterium see discussion under mass spectra. (w) Preparation of 2-methylayclohexanone-2,6,6-d7, o The same procedure as outlined under (b) was followed using 5 g of commercially available 2-methylcyclohexanone (Aldrich Chemicals). - 37 -(x) Preparation of 2-rnethylcyclohexanol The procedure used i s as under (c) reacting one gram of 2-methyl-cyclohexanone and LiAlH^. The alcohols obtained were purified and collected by gas-liquid chromatography. The same conditions as under (o) prevailed except that the carrier gas flow rate was 75 ml/min. Retention times cis 2-methylcyclohexanol 20 min trans 2-methylcyclohexanol 27 min Stereochemical assignments from the relative retention times agree with the product ratio expected from lithium aluminum hydride reduction (10). Cy) Preparation of cis and trans 2-methylcyclohexanol-l-d^3 cis and trans 2-methylcyclohexanol-23636-d^3 cis and trans 2-methylcyclo-hexanol-l323636-d^ The same procedure as under (c) was followed, the appropriate ketone and hydride being used. The alcohols obtained were purified and collected as under (x). Due care was taken to purify and collect the isomers prepared. The purity of the separated isomers was double checked by vapour phase chromatography. - 38 -Part B: Mass Spectra The instrument used for this work is an Associated E l e c t r i c a l Industries M.S. 902 mass spectrometer. This is a double focussing magnetic scanning instrument capable of a resolution of up to 50,000. The conventional electron impact ion source has been replaced by a modified dual photoionisation and electron impact source (46,47). The source of photons used was the low pressure microwave discharge which was f i r s t used by Frost and McDowell (48) for photoionisation mass spectrometry and subsequently for photoelectron spectroscopy. The majority of the radiation obtained in a pure helium discharge o has a wavelength of 584.3 A corresponding to an energy of 21.21 eV. This line arises from the 2^P—^l^S resonance transition in helium (49). The other source of photons uti l i z e d was the low pressure microwave ' discharge in a hydrogen-helium mixture. This produces the Lyman o radiation 1215.7 A corresponding to an energy of 10.19 eV due to 22P—>-l2S transition. Figure 4 shows a diagram of the light source used. A needle valve controls the flow of commercial helium into the quartz tube at a pressure of approximately 1 mm Hg. The pressure in the discharge region i s also stabilized by a constriction at the other end of the quartz tube which also serves to f a c i l i t a t e d i f f erential pumping of the helium between the light source and the ionization chamber. In order to prevent excessive helium from entering the mass spectro-meter the lower portion of the source consists of a short brass tube which protrudes through the source housing. This capillary allows a narrow light beam to be transmitted while impeding the flow of helium. A pumping line situated close to the mouth of the capillary 2450 M/cs microwave cavity pumps PHOTOIONIZATION S O U R C E (II) Fig. 4. gas inlet - 40 -pumps away the excess helium. The discharge is produced in the cavity by power from a "Microtron 200" microwave generator, and is initiated with a Tesla c o i l . The quartz tube i s cooled with compressed air to prevent melting. The Lyman a radiation was produced by introducing commercial tank hydrogen, using a needle valve to control the flow into the quartz tube through which helium was already flowing. A maximum ion beam was obtained when an approximately 50:50 mixture was used. Low resolution mass spectra with source and collector s l i t s completely open (resolving power approximately 750) were obtained for a l l samples studied using both the helium resonance line, and the hydrogen Lyman a light sources. The conditions under which the light sources were operated was kept as constant as possible, taking special care to eliminate the presence of any air impurities. A l l spectra were also recorded under conditions as identical as possible; the machine settings being the same for a l l spectra. The base pressure before introduction of the sample in the source measured by an ionisation gauge which is located just above the source diffusion pump, ~6 —6 was 0.8 x 10 torr and 1.6 x 10 torr for the helium and Lyman a light sources respectively. These pressures were found to give optimum intensity. Since a l l the samples studied were sufficiently volatile at room temperature, they were introduced into the spectrometer through a direct inlet system. Freeze thaw cycles were used to degas the samples. The amount of sample introduced into the spectrometer was controlled by valves so that the pressure in the source was constant. - 41 -Typical pressures at which runs were made are as follows. With —6 the Lyman a light source the sample partial pressure was 2.0 x 10 torr, whereas with the helium light source a sample partial pressure of 3.0 x 10 ^  torr was used. High resolution measurements (R.P. = 10,000) were made on a l l major peaks in the spectra of the non-deuterated Isomers of each series. The reference compound used was heptacosafluorotributylamine. Instructions on operating the mass spectrometer and on obtaining a spectrum may be found in reference 50. - 42 -RESULTS The spectra obtained in the course of this investigation have been presented in the form of drawings relating the relative abundance (left ordinate) of the fragments to their mass to charge ratios (abscissa). The values for the fragment ions in terms of the percentage of the total ionisation are shown on the right side of the diagram. These values were obtained by summing a l l the ions from the molecular ion to a certain m/e value as indicated by the subscript (E ) and calculating the intensity of fragments in terms of the percentage of the total ionisation. Only ions greater than 1% of the base peak have been shown. Direct comparison of the intensity of fragment ions in terms of their percentage of total ionisation i s meaningful in the case of isomers since i t has been shown (by electron impact (6)) that the cross section obtained for isomers i s the same regardless of their structure. A direct inlet system was used to introduce a l l the samples studied. In order to determine whether the inlet system had any effect on the observed mass spectra runs were made using the direct insertion probe on both cis and trans 4-t-butylcyclohexanols. No - 43 -differences were observed in the spectra from those obtained with the direct inlet system. A study was also made to see whether the sample pressure had any affect on the mass spectrum. Variation of the sample pressure between 1.0 x 10 ^ and 6.0 x 10 ^ torr showed no significant changes. However significant differences were observed when air was introduced deliberately into the light source when generating the helium radiation. The production of lower energy lines (from 0^ or N ) is probably responsible for this effect (51). In view of this,special care was taken to purge the system to minimise these effects. In order to determine the reproducibility of the measurements the spectrum of trans-4-t-butylcyclohexanol (helium light source) was obtained a number of times over a period of a few months. Large peaks greater than 20% of the base peak were found to vary within 10% of a mean value whereas smaller peaks had a larger variation of approximately 20%. The reproducibility of the results was affected mainly due to the inaccuracy in determining the peak heights. The high multiplier gain used to obtain the spectra resulted in peaks having a considerable amount of noise at the top. Due to the method of assigning the peak height (measured approximately to the middle of the noise region) relatively large errors would be introduced x^ hen measuring small peaks compared to that of larger peaks. Small variations in sample pressure and slight changes in the operating conditions of the light source may also contribute to the error. The value quoted in the discussion for the mass position of an observed metastable "peak" due to a specific metastable transition was - 44 -obtained directly from the low resolution spectrum. A. Cis and trans 4-t-butylcyclohexanols The spectra obtained using both the helium light source and the Lyman a light source for these alcohols and their deuterated counterparts are shown in Figures 5 to 14 on pages 95 to 99. He light Lyman a source light source Trans and cis 4-t-butylcyclohexanol Fig. 5 Fig. 6 Trans and cis 4-t-butylcyclohexanol-l-d^ Fig. 7 Fig. 8 Trans and cis 4-t-butylcyclohexanol-2,2,6,6-d^ Fig. 9 Fig. 10 Trans and cis 4-t-butylcyclohexanol-l,2,2,6 ,6-d,. Fig. 11 Fig. 12 Trans and cis 4-t-butylcyclohexanol-(CD^) y d ^ Fig- 13 Fig. 14 For the spectra obtained with the Lyman a light source the amount of isotope incorporated was determined by the method of Biemann (6) using the undeuterated alcohols as standards. Since no peak correspon-ding to [M-l] + ion is present in the spectra obtained under these conditions no complications arise in the calculations. However, the spectra of the undeuterated alcohols obtained with the helium light source do have a [M-l] + ion present. In the deuterated compounds, since one cannot assume that the spectra w i l l be merely shifted by one or more mass units keeping the intensities constant, d i f f i c u l t i e s arise in the determination of isotope content. Therefore, in these cases only the results from the spectra obtained with the Lyman a light source were used to determine the extent of labelling. - 45 -The results calculated are as follows for cis and trans 4-t-butylcyclohexanol. These were obtained using the parent peak abundance values. Lyman a light source trans 4-t-butylcyclohexanol-l-d^ 100% d L trans 4-t-butylcyclohexanol-2,2,6,6-d^ 7.0% d3 93.0% d4 trans 4-t-butylcyclohexanol-l,2,2,6,6-d,. 3.8% d4 96.2% d5 trans 4-t-butylcyclohexanol-(CD^) 2.1% d l 0.9% d2 12.5% d8 84.5% d9 cis 4--t-butylcyclohexanol-l-d^ 12.6% do 87.4% d l cis 4--t-butylcyclohexanol-2,2,6,6-d^ 3.0% d3 97.0% d4 cis 4-• t-butylcyclohexanol-1,2,2,6,6-d,_ 4.0% d4 96.0% d5 cis 4--t-butylcyclohexanol-(CD^)3-dg 2.2% d l 1.5% d2 0.5% d3 0.4% d4 0.2% d5 0.2% d6 0.9% d7 11.0% d8 83.1% d9 - 46 -The high resolution data obtained are as follows: Trans 4-t-butylcyclohexanol m/e 1.38 123 110 99 95 83 82 81 80 67 57 56 He light source C10 H18 C9 H15 C8 H14 C 6H uO C7 H11 C6 H11 C6 H10 C6 H9 C6 H8 C 5H 7 C.Hn ^90.0% 4 9 C ^ O ^10.0% C4 H8 Lyman a light source C10 H18 C9 H15 C8 H14 C6 H11° C6 H11 C6 H10 C6 H9 C6 H8 C4 H9 C ^ O (trace) C4 H8 Cis 4-t-butylcyclohexanol m/e He light source 123 99 98 83 82 81 80 C9 H15 C6 H11° C6 H10° C6 H11 C6 H10 C6 H9 C6 H8 Lyman a light source C9 H15 C 6 H H ° C6 H10° C6 H11 C6 H10 C6 H9 C6 H8 - 47 -67 C H ? 57 C.H. ^90.0% C.H_ 4 9 4 9 C ^ O ^10.0% C3 H5° ^ t r a c e ^ 5 6 C4 H8 C4 H8 B. Cis and trans 4-t-butylcyclohexyl acetates The spectra obtained using both light sources for the acetates are shown in figures 15 to 24 on pages 113 to 117. He light Lyman a source light source trans and cis 4-t-butylcyclohexyl acetate Fig. 15 Fig. 16 trans and cis 4^-t-butylcyclohexyl acetate-l-d^ Fig. 17 Fig. 18 trans and cis 4-t-butylcyclohexyl acetate-2,2,6,6-d4 F i g > l g trans and cis 4-t-butylcyclohexyl acetate-Fig. 20 1,2,2,6,6-d Fig. 21 Fig. 22 trans and cis 4-t-butylcyclohexyl acetate-(CD 3) 3-d 9 Fig. 23 Fig. 24 Since the parent ion in these molecules i s very small in abundance no estimation of deuterium content could be made directly from the spectra. However, since they were prepared from the corres-ponding dueterated alcohols an assumption can be made that the isotope content remains the same, and that no loss incurred i n the preparation of the acetates. High resolution measurements on the acetates gave the following results. - 48 -Trans and cis 4-t-butylcyclohexyl acetates m/e He light source Lyman a light source 1 3 8 C10 H18 C10 H18 123 C 9H 1 5 C 9H 1 5 117 C 6H 1 30 2 C 6H 1 30 2 83 C 6 H U C 6 H U 8 2 C6 H10 C6 H10 8 1 C6 H9 C6 H9 80 C6Hg C 6H g 67 C 5H y 61 C 2H 50 2 C 2H 50 2 5 7 C4 H9 C4 H9 56 C 4H 8 C. Cis and trans 4-t-butylcyclohexyl methyl ethers The spectra obtained for cis and trans 4-t-butylcyclohexyl methyl ethers and their deuterated derivatives (using both light sources) are shown in Figures 25 to 34 on pages 135 to 140. He light Lyman a source light source trans and cis 4-t-butylcyclohexyl methyl Fig. 25 Fig. 26 ether trans and cis 4-t-butylcyclohexyl methyl Fig. 27 Fig. 28 ether-l-d^ trans and cis 4-t-butylcyclohexyl methyl Fig. 29 Fig. 30 ether-2,2,6,6-d^ - 49 -trans and cis 4-t-butylcyclohexyl methyl ether-l,2,2,6,6-d Fig. 31 Fig. 32 trans and cis 4-t^butylcyclohexyl methyl ether-(CD 3) 3-d 9 Fig. 33 Fig. 34 The extent of deuteration in the various deuterated molecules was determined from the mass spectra using parent peak abundance values. The results obtained are as follows: He light Lyman a source light source trans 4-t-butylcyclohexyl methyl ether-l-d 1 1.7% d Q 2.0% d Q 98.3% d 98.0% d trans 4-t-butylcyclohexyl methyl ether- 4.3% d 3 5.1% d 3 2,2,6,6-d4 95.7% d 4 94.9% d 4 trans 4-t-butylcyclohexyl methyl ether- 4.4% d 4 4.5% d 4 1,2,2,6,6-d 95.6% d $ 95.5% d $ trans 4-t-butylcyclohexyl methyl ether- 11.2% d Q 9.7% d„ o o (CD 3) 3-d g 88.8% d g 90.3% d g cis 4-•t-butylcyclohexyl methyl ether-l-d^ 14.4% do 13.9% do 85.6% d l 86.1% d l cis 4-•t-butylcyclohexyl methyl ether- 8.4% d3 5.6% d3 2,2,6,6,d4 91.6% d4 94.4% d4 cis 4-•t-butylcyclohexyl methyl ether- 10.0% d l 7.8% d l 1,2,2,6,6—d^ 3.2% d2 4.5% d2 4.3% d4 6.7% d4 82.5% d5 81.0% d5 - 50 -cis 4-t-butylcyclohexyl methyl ether-CCD 3) 3-d 9 8.7% d l 8.7% d l 8.9% d2 9.9% d2 8.9% d3 9.1% d3 4.9% d4 5.5% d4 3.0% d5 3.7% d5 2.1% d6 1.8% d6 1.6% d7 2.0% d7 11.5% d8 10.9% d8 50.4% d9 48.4% d9 High resolution data obtained for both cis and trans 4-t-butyl-cyclohexyl methyl ethers are as follows: Trans 4-t-butylcyclohexyl methyl ether m/e He light source Lyman a light so 138 C10 H18 C10 H18 123 C9 H15 C 9H 1 5 (trace) 113 C 7H 1 30 C ?H 1 30 110 C8 H14 C8 H14 83 C6 H11 C,H.. _ (trace) o 1 1 82 C6 H10 C 6H 1 ( ) (trace) 81 C6 H9 C6 H9 80 C6 H8 C6 H8 71 C.H.,0 4 7 C.H.,0 (trace) 4 7 •'7 C 5H 7 — 57 C4 H9 C^H9 (trace) - 51 -Cis 4-t-butylcyalohexyl methyl ether m/e He light source Lyman a light sou 138 C10 H18 C10 H18 123 C9 H15 C9 H15 115 C yH 1 50 C7 H15° 114 C7 H14° C7 H14° 113 C7 H13° C 7H 1 30 112 C yH 1 20 C ?H 1 20 83 C6 H11 C6 H11 82 C6 H10 C6 H10 81 C6 H9 C6 H9 80 C6 H8 C6 H8 71 C.H.,0 4 7 C ^ O (trace) 67 C5 H7 — 57 C4 H9 C^ Hg (trace) D. The methylcyclohexanols 1. Cis and trans 4-methylcyclohexanols The spectra obtained for cis and trans 4-methylcyclohexano]s and their deuterated derivatives (using both light sources) are shown i n figures 35 to 42 on pages 152 to 155. trans and cis 4-methylcyclohexanol trans and cis 4-methylcyclohexanol-l-d^ trans and cis 4-methylcyclohexanol-2,2,6,6-d, He light source Fig. 35 Fig. 37 Fig. 39 Lyman a light source Fig. 36 Fig. 38 Fig. 40 - 52 -trans and cis 4-methylcyclohexanol- Fig- 41 Fig. 42 1,2,2,6,6-d,. The extent of deuteration in the various deuterated molecules was determined from the mass spectra using the parent peak abundance values. (Only the results from the Lyman a light source were utilized.) The results obtained are as follows: Lyman a light source trans 4-methylcyclohexanol-1-d^ 6.6% do 93.4% d l trans 4-methyIcyclohexanol-2,2,6,6-d^ 6.8% d3 93.2% d4 trans 4-methylcyclohexanol-l,2,2,6, 6-d,_ 13.7% d4 86.3% d5 cis 4-methylcyclohexanol-1-d^ 0.5% do 99.5% d l cis 4-methylcyclohexanol-2,2,6,6-d^ 0.9% d2 5.2% d2 93.9% d4 cis 4-me thylcyclohexanol-1$ 2,2,6,6-d,. 0.2% d l 0.2% d2 0.6% d3 6.1% d4 92.9% d5 - 53 -High resolution data obtained for both cis and trans 4-methylcyclo-hexanols are as follows: Cis and trans 4-methylcyelohexanols m/e He light source Lyman a light source 96 C yH 1 2 C ?H 1 2 81 C 6H 9 C 6H 9 71 C 5 H n C 5 H l l 7 0 C5 H10 C5 H10 58 CoH,0 CoHr0 3 6 3 6 57 C3 H5° ^ 7 5 % C3 H5° C 4H 9 ^25% C 4H 9 2. Cis and trans 3-methylcyclohexanols The spectra obtained for cis and trans 3-methylcyclohexanols and their deuterated derivatives (using both light sources) are shown in figures 43 to 52 on pages 164 to 168. He light Lyman a source light source trans and cis 3-methylcyclohexanol Fig- 43 Fig- 44 trans and cis 3-methylcyclohexanol-l-d^ Fig. 45 Fig. 46 trans and cis 3-methylcyclohexanol-2,2,6,6-d4 Fig. 47 Fig. 48 trans and cis 3-methylcyclohexanol-1,2,2,6,6-d Fig. 49 Fig. 50 trans and cis 3-methylcyclohexanol-4,4-(CD3)-d5 Fig. 51 Fig. 52 - 54 -The extent of deuteration in the various deuterated molecules was determined from the mass spectra using the parent peak abundance values. (Only the results from the spectra obtained with the Lyman a light source were utilized.) The estimations obtained are as follows: Lyman a light source trans 3-methylcyclohexanol-l-d^ 12.4% do 87.6% d l trans 3-methylcyclohexanol-2,2,6,6-d^ 8.9% d3 91.1% d4 trans 3-methylcyclohexanol-1,2,2,6,6-d^ 8.6% d4 91.4% d5 trans 3-methylcyclohexanol-4,4-(CD3)-d^ 2.9% do 14.7% d4 69.4% d5 13.0% d6 cis 3-methylcyclohexanol-l-d^ 5.0% do 95.0% d l cis 3-me thylcyclohexanol-2,2,6,6-d^ 10.2% d3 89.8% d4 cis 3-methyIcyclohexanol-1,2, 2,6,6-d,. 6.3% d4 93.7% d5 cis 3-methylcyclohexanol-4,4-(CD^)-d,. 3.2% do 5.0% d l 5.3% d3 11.8% d4 68.2% d5 6.5% d6 - 55 -High resolution data obtained for both cis and trans 3-methylcyclo-hexanol are as follows: Cis and trans 3-methylcyclohexanols m/e He light source Lyman a light source 96 C ?H 1 2 C 7H 1 2 8 1 C6 H9 C6 H9 71 C.H.,0 a,95% C.H.,0 4 7 4 7 C 5 H u ^ 5% 5 7 C3 H5° ^ 8 0 % C.H- ^20% 4 9 55 C.H_ 4 7 3. Cis and trans 2-methylcyclohexanols The spectra obtained for cis and trans 2-methylcyclohexanols and their deuterated derivatives (using both light sources) are shown in figures 53 to 60 on pages 175 to 178. He light Lyman a source light source trans and cis 2-methylcyclohexanol Fig- 53 Fig. 54 trans and cis 2-methylcyclohexanol-l-d^ Fig. 55 Fig. 56 trans and cis 2-methylcyclohexanol-2,6,6-d^ Fig- 57 Fig. 58 trans and cis 2-methylcyclohexanol-l,2,6,6-d. Fig. 59 Fig. 60 The extent of deuteration i n the various deuterated molecules was determined from the mass spectra using the parent peak abundance values. The results obtained as as follows: - 56 -trans 2-^methylcyclohexanol-l-d^ trans 2-methylcyclohexanol-2,6,6-d ^ trans 2-methylcyclohexanol-l,2,6,6-d cis 2-methylcyclohexanol-l-d^ cis 2-methylcyclohexanol-2,6,6-d^ cis 2-methylcyclohexanol-l,2,6,6-d^ High resolution data obtained for hexanolsare as follows: Cis and trans 2-methylcyclohexanols m/e He light source 96 C-, H.. _ 7 12 81 C,H_ 6 9 71 C.H_0 4 7 68 C5 H8 57 C„H rO 3 5 C^ Hg (trace) Lyman a light source 10.0% do 90.0% d l 4.4% d i 6.1% d2 89.5% d3 1.4% d2 5.8% d3 92.8% d4 4.8% do 95.2% d l 2.9% d l 5.6% d2 91.5% d3 7.2% d3 92.8% d4 both cis and trans 2-methylcyclo-Lyman a light source C4 H7° C 5H g - 57 -DISCUSSION Studies of reaction mechanisms attempt to analyse the way in which compound A is transformed to compound B generally in terms of elementary steps and stereochemistry. In solution chemistry the structures of A and B are usually known and mechanistic information may be deduced from kinetic studies, solvent effects, stereochemistry, isotopic labelling and other slight structural modifications. In mass spectrometry, mechanistic problems are more complicated because the structures of ions and their fragmentation products have not been studied directly. A l l the methods used to investigate ion structures involve comparisons amongst ions and except for a few simple molecules no ion structures have been determined precisely. In this discussion the concept of charge and radical localisation w i l l be utilized to discuss the results obtained. To simplify matters and for p i c t o r i a l convenience the decomposition of an excited ion formed from a molecule w i l l be represented in terms of the structure of the intact molecule. This does not imply that the "ion structures" drawn necessarily represent the actual structure of the ion or that fragmentation reactions take place in a stepwise fashion as indicated in the schemes. Some of these reactions may occur in a concerted fashion, whereas others may take place in a stepwise manner. - 58 -Probably the single most useful technique in mechanistic studies in mass spectrometry has been the use of isotopically labelled molecules especially those labelled with deuterium. If i t i s assumed that the position of labelled atoms in a molecular ion corresponds to that in the neutral molecule from which the ion is formed, then a knowledge of the fate of the label i n subsequent fragmentations allows the proposal of reasonable ion structures. However, i t has been observed that under certain conditions scrambling of the labels may result (52,53). The occurrence of such processes makes the incorpora-tion of a label into a fragment ion non-specific and thus complications occur because i t is d i f f i c u l t to distinguish a specific process in competition with label scrambling from non-specific processes (54). It has further been observed (55) that as the ionising energy is lowered scrambling of labels increases. This has been explained in terms of the longer lifetimes of ions having less energy (56,57). The conditions under which the spectra have been obtained in this work would necessarily lead to ions of longer lifetime than those obtained with 70 eV electrons. Whether such scrambling reactions do occur is d i f f i c u l t to assess. However, i t w i l l be assumed that the positions of labelling remain the same as in the neutral molecule unless otherwise suspected from an examination of the mass spectrum. The following discussion w i l l be divided into five main sections each dealing with a detailed study of the spectra obtained, as outlined below: A. Cis and trans 4-t-butylcyclohexanols B. Cis and trans 4 - t - b u t y l c y c l o h e x y l acetates C. Cis and trans 4 - t - b u t y l c y c l o h e x y l methyl ethers D. C i s and trans isomers of 4, 3, and 2 s u b s t i t u t e d methyl cyclohexanols E. General observations A. Cis and trans 4-t-butylcyclohexanols The s p e c t r a obtained f o r c i s and trans 4-t-butylcyclohexanols o using the He 584 A l i g h t source are shown i n F i g . 5. These s p e c t r a agree q u a l i t a t i v e l y w i t h those obtained by B r i o n and H a l l (18) using the same l i g h t source and by Doljes and Hanus (19) using an e l e c t r o n impact source. However, s i g n i f i c a n t d i f f e r e n c e s are observed i n the r e l a t i v e abundances of some ions i n the s p e c t r a . Since the s p e c t r a obtained by B r i o n and H a l l were run on the same machine,the d i f f e r e n c e s observed may be a t t r i b u t e d to i m p u r i t i e s i n the l i g h t source i n the e a r l i e r work. A lower energy l i n e from a or 0^ i m p u r i t y may be p a r t l y r e s p o n s i b l e f o r i o n i s a t i o n , thus i n c r e a s i n g the r e l a t i v e abundance of fragment ions which are products of molecule ions w i t h lower i n i t i a l energy content. These impurity l i n e s have a l s o been r e s p o n s i b l e f o r some features observed i n photoelectron s p e c t r a where s i m i l a r l i g h t sources were u t i l i z e d (51,58). The s p e c t r a obtained using the Lyman a l i g h t source are shown i n F i g . 6. I o n i s a t i o n of these compounds i s probably due to l o s s of one of the non-bonding e l e c t r o n s on the oxygen atom (59). This creates a h i g h l y r e a c t i v e r a d i c a l which i s l i m i t e d to p a r t i c i p a t i o n i n an i n t r a -- 60 -molecular reaction. The unpaired electron of the oxygen atom can thus form a new bond which perhaps is the powerful driving force in decomposition reactions of ions of this type. Returning to Fig. 5 a comparison of the spectra of the two isomers leads to the following observations. (1) The abundance of the parent peak is greater in the cis isomer (2.4% of E^) than in the trans isomer (0.5% of E^) • (2) The abundance of the [M-F^ O]"*" ion in the trans isomer (16.4% of E^) is greater than in the cis isomer (0.2% of E^) • (3) The absence of the ion at m/e 110 in the cis isomer. (4) The larger relative abundance of the ion at m/e 99 in the cis isomer (9.5% of E^) as compared to the trans isomer (4.8% of E ^ ) . (5) The base peak in both isomers is at m/e 57. The same general observations can be made for the spectra obtained with the deuterated analogues, (Figs. 7,9,11,13) taking into account the shifts due to isotope incorporation in certain fragments. Figures 6, 8, 10, 12 and 14 show the spectra obtained using the Lyman a line for ionisation. The same general features are present as in the spectra obtained with the helium light source. However, in this case the base peak in the trans isomer is at m/e 138 and at m/e 99 in the cis isomer. The fact that differences are observed in the spectra of the two isomers suggests that cleavage of the ring does not take place immediately after ionisation. If ring opening occurred preceding any fragmentation reactions there would no longer be any difference between the isomers and the spectra obtained should be almost identical. - 61 -The major difference, as mentioned before, in the spectra of the two epimers is in the relative abundance of the [M-l^ O]"*" ion and the ion at m/e 99. Since the formation of these ions is probably dependent on the attainment of specific transition states they may be indicative of the spatial distribution of the atoms in the respective isomers. An attempt w i l l therefore be made to analyse the data obtained and to assess the validity of such an approach in dealing with mass spectral fragmentation reactions. The possible modes of formation of the [M-I^O] ion and the ion at m/e 99 w i l l be discussed followed by an attempt to explain the formation of other common ions present in both isomers. Schemes 1 and 2 show the major fragmentation routes involved in the decomposition of the trans and cis alcohols respectively. A-1. The [M-H£G]+ ion The mode of elimination of water in these alcohols has been of considerable interest to many workers in the f i e l d (19,20). The values obtained for the [M-t^O^/M"1" ratio are shown in Table 1. These results are in general agreement with those obtained by other workers (18,19,20) indicating preferential loss of water in the trans isomer. While there i s a variation observed in the value of + + [M-F^O] /M from one deuterated analogue to another of the same isomer, which could be attributed to isotope effects and/or instrumental factors, the relative proportions of this ratio for the two isomers are nearly constant in the case of each deuterated analogue examined. From Figures 7(a), 9(a), 11(a), and 13(a) i t is evident that the - 62 -Scheme 1 Trans 4-t-butylcyclohexanol - 63 -Scheme 2 C4 H9 m/e 83 C10 H18^ m/e 138 -CH, + C9 H15 C6 H9 ,-C4H9 + m/e 123 m/e 81 C6 H10 l/e 82 C6 H11° i/e 99 + + C5 H7 m/e 67 C6 H11° m/e 99 -H C 6 H 1 0 0 t C9 H17° m/e 141 -C 3H 7 + C6 H8 _ H 0 m/e 80 2 m/e 98 Cis 4-t-butylcyclohexanol - 64 -Table I, [M-H20]+/M+ Ratio for Cis and Trans 4-t-Butylcyclohexanols, and Their Deuterated Analogues (both light sources) + + a [M-H20] /M + +b [M-H20] /M trans 4-t-butylcyclohexanol 31.2 24.2 trans 4-t-butylcyclohexanol-l-d^ 30.0 30.0 trans 4-t-butyIcyclohexanol-2,2,6,6-d^ 45.0 32.5 trans 4-t-butylcyclohexanol-l,2,2,6,6-d,. 41.6 36.9 trans 4-t-butylcyclohexanol-(CD^)3-dg 28.6 22.4 cis 4--t-butylcyclohexanol 0.06 0.04 cis 4-•t-butylcyclohexanol-l-d^ 0.05 0.08 cis 4-•t-butyIcyclohexanol-2,2,6,6-d^ 0.03 0.02 cis 4--t*-butylcyclohexanol-l, 2,2,6 , 6-d,. 0.04 0.02 * A cis 4--t-butylcyclohexanol-(CD^)3-dg 0.26 0.22 Degeneracy due to [M-CD^ ] which appears at the same m/e value. Helium light source Lyman a light source - 65 -water molecule lost in the trans isomer does not involve the protons at C-l, C-2, or C-6 or from the tertiary butyl substituent. This implies that the proton lost together with the hydroxyl group originates either from the hydrogen attached at C-4 or from the hydrogens at C-3 (or C-5). It has been suggested (18) that the elimination in the trans isomer goes via the boat conformation of the ring thus leading to a 1,4-type mechanism as shown in Fig. 61. This situation i s not possible Figure 61. Possible transition state conformation resulting in loss of water by a 1,4-mechanism. for the cis isomer in any conformation with the ring intact, since the hydroxyl group never comes as close to the hydrogen atom at C-4 as in the trans isomer. The same type of stereospecific loss in cyclohexanol has been discussed by Green and Schwab (60) who have shown from labelling results that the cis hydrogen from position four i s lost. More recently, - 66 -Green et a l . (2) have reported having synthesized 4-t-butylcyclohexanol-4-d^ and have made the observation that a l l of the hydrogen eliminated with the hydroxyl group is from position four in the trans isomer. Attempts were made to synthesize this specifically deuterated alcohol in the present work, however, no success was achieved. The loss of hydrogen from carbon four is further favoured in this alcohol because the proton lost i s a tertiary hydrogen and i s further labilized by the large alkyl substituent. Evidence for preference of abstraction of a tertiary hydrogen compared to a secondary or a primary hydrogen comes from the work of Budzikiewicz et a l . (61). The above mentioned factors point to the fact that the major elimination pathway in the trans alcohol i s via a boat conformation. Furthermore,the subsequent decomposition of the [M-H^ O]^ " ion may provide insight as to the structure of this ion. The two main po s s i b i l i t i e s being the bicyclic form with a partial bond between C-l and C-4 or the flexible form suggested by Meyerson (3). The ion at m/e 123 in the trans isomer most probably arises from the decomposition of the [M-H^ O]"*" ion. The appearance of metastable ions further corroborates this. Such metastable ions are li s t e d in Table II. bicyclic form flexible form - 67 -Table II. Observed m/e Value for ion m* Resulting from Metastable Transition 138 ->- 123 in Trans 4-t-Butylcyclohexanol and for the Corresponding Transition in the Trans Deuterated Analogues. m* m* m, m trans 4-•t--butylcyclohexanol 109.6 109. 6 138 123 trans 4-•t--butylcyclohexanol-l-d^ — 110. 6 139 124 trans 4-•t--butylcyclohexanol-2,2,6,6-d^ 113.5 113. 5 142 127 trans 4-•t--butylcvclohexanol-l,2,2,6,6-d5 114.5 114. 5 143 128 trans 4-•t--butylcyclohexanol- 113.2 — 147 129 (CD 3) 3-d 9 Lyman a light source; Helium light source From the deuterium labelled trans isomer [Figs. 7(a), 8(a), 9(a), 10(a), 11(a), 12(a), 13(a), and 14(a)] one observes that the a and g hydrogens of the ring as well as two methyl groups of the tertiary butyl side chain are incorporated in this ion. The following scheme thus symbolises i t s formation. - 68 -m/e 123 2 The flexible form of the ring with two sp hydridized ring carbons (one and four) could possibly be a favourable structure for the [M-H^ O]"^  ion from which this fragmentation reaction takes place. The suggestion arises from the fact that i f the ion at m/e 123 has the 2 structure as indicated, then C-4 would have to be sp hydridized with the p orbital forming a Tf-bond with the p-orbital of the rehybridized 2 sp carbon at the central carbon of the tertiary butyl group. It 2 has been suggested that a cyclohexane ring with two or more sp hybridized ring atoms is more stable in the flexible form (62). - 69 -The ion at m/e 110 in the trans isomer also most probably has the [M-R^ O] ion as i t s precursor. This would imply loss of 28 mass units. An abundant ion corresponding to loss of the same number of mass units is also observed in the mass spectrum of bicyclo[2.2.0]hexane (63) + thus suggesting that the [M-R^ O] ion in this case may have a similar structure and fragments in a similar fashion. Its mechanism of formation may be postulated to occur as follows: m/e 156 m/e 138 m/e 110 Deuterium labelling results (Figs. 7(a) and 8(a)) indicate that the proton at C-l i s retained in this fragment ion and also verifies the loss of hydrogens associated with C-2 (or C-6) [Figs. 9(a), 10(a), 11(a), and 12(a)] thus implying loss of the corresponding carbon as well. Figures 13(a) and 14(a) further indicate the presence of the. tertiary butyl group in this fragment ion. The st a b i l i t y of the neutral molecule lost may be the driving force for this reaction since the postulated unsaturated cyclobutane ring is probably not a very stable ion due to the ring strain involved. This would therefore decompose quite readily to form other fragment ions. This reaction mechanism seems to suggest that the bicy c l i c ion - 70 -form of the [M-H^ O]"*" ion may be the favoured structure, partial bond formation between C-l and C-4 having already taken place. This would further explain the absence of this ion in the spectrum of the cis isomer. Since no water loss can ,occur by a 1,4-mechanism in this case, there is no likelihood of forming the bicyclohexane type of ion thus eliminating the possibility of formation of the ion at m/e 110. Finally the [M-H^ O]"*" ion in the trans isomer may also lose the tertiary butyl group to form an ion at m/e 81. Deuterium labelling results verify the incorporation of the a and 3 protons in this fragment ion [Figs. 7(a), 8(a), 9(a), 10(a), 11(a) and 12(a)] and the loss of the tertiary butyl group [Figs. 13(a) and 14(a)]. The following scheme rationalizes i t s formation. /e 156 m/e 138 m/e 81 Assuming the ring is s t i l l intact the above mechanism favours a bicyclic type of structure for the [M-R^O^ ion. It is possible, however, that loss of the tertiary butyl group may precede the loss of water. From the foregoing discussion i t is d i f f i c u l t to assign a 4-specific structure to the [M-H 0] ion. It i s possible that intermediat - 71 -structures may exist which have a form between the two alternatives suggested. The [M-H^ O]"^  ion in the cis isomer is most probably formed mainly by a 1,3-mechanism. The very small abundance of these ions may be due to the following reasons: (1) The molecular ion has in this case other more favourable modes of decomposition and therefore only a few eliminate water by a direct 1,3-mechanism. (2) The st a b i l i t y of the [M-I^ O]"*" ion in the cis isomer is much lower than in the corresponding ion in the trans isomer and therefore i t decomposes more readily. A-2. The ions at m/e 99 and m/e 98 The ion at m/e 99 is the base peak in the spectrum of the cis isomer obtained with the Lyman a light source. Figure 6(b) indicates this. The larger relative abundance of the ion at m/e 99 is also present in the spectrum of the cis isomer obtained with the helium light source [Fig. 5(b)] but the difference i s not as striking. From high resolution measurements the ion at m/e 99 is found to be C.H^O4". 6 11 The formation of this ion in the cis isomer has been postulated to occur by cleavage of the tertiary butyl group (20) which preempts the 1,3-elimination of water which is a relatively slower process. Green et a l . (2), working with deuterated derivatives of cyclohexanol have come to the conclusion that carbon-carbon bond cleavage always preceeded elimination of water by a 1,3-process, thus giving support - 72 -to the statement made above. From the deuterium labelling studies a major portion of the ions corresponding to m/e 99 is found to remain at m/e 99 in the spectrum of cis 4-t-butylcyclohexanol-l-d^ [Fig. 8(b)] and appears at m/e 103 in the spectrum of cis 4-t-butylcyclohexanol-l,2,2,6,6-d,. [Fig. 12(b)]. This, therefore, implies that the hydrogen at C-l is not involved in this ion. Simple cleavage of the tertiary butyl group would account for a small contribution to the ion at m/e 99 in the undeuterated cis alcohol [Fig. 6(b)], which would in the case of cis 4-t-butylcyclohexanol-1-d^ show up at m/e 100 and in the case of cis 4-t-butylcyclohexanol-1,2,2,6,6-d,. at m/e 104. Furthermore, a degeneracy i s also created at m/e 99 in Fig. 8(b) and at m/e 103 in Fig. 12(b) due to the ion originally present at m/e 98 in the non-deuterated cis isomer [Fig. 6(b)]. Simple cleavage of the tertiary butyl group does not explain the formation of the majority of these ions and therefore some other mechanism has to be considered. According to McLafferty (59) stable even electron ions containing a heteroatom may have an additional bond to the heteroatom which i s made possible i n this case by the ut i l i z a t i o n of the non-bonding orbital of the oxygen atom. Since the ion at m/e 99 i s an even electron ion, i t therefore, may have two bonds to oxygen besides the r carbon oxygen bond. If the energetics of the photoionization process allows one to rationalize that the trans isomer in some of it s excited states assumes the boat conformation then i t is just as possible that this / - 73 -can also occur in the cis isomer. The excess energy associated with the cis isomer may further contribute to this process. One of the rationalizations for the presence of an ion at m/e 99 makes use of this possibility. If the cis isomer can f l i p into a flexible form,(Fig. 62) the tertiary butyl group and the hydroxyl group can come sufficiently close so that the hydroxyl group (radical after ionization) can abstract a hydrogen from the side chain. Although the hydrogen abstracted would Figure 62. A possible transition state conformation from which the hydroxyl group can readily abstract a hydrogen originating from the alkyl substituent. be a primary hydrogen, in the absence of any other being available, this might s t i l l take place. Perhaps, the energetics of the reaction are such that the fi n a l stabilization i s the driving force. Therefore instead of eliminating a water molecule the elimination of the C.HQ lteutral species takes place. The loss of this group would greatly release the steric strain present in the molecular ion with the tertiary butyl group in an axial or semi-axial position. However, as mentioned before the loss of the C-l hydrogen also takes place and somehow i t has to be accommodated in the mechanism. The loss of this H 3C' , ^ C H 3 CH - 74 -H m/e 99 hydrogen most probably occurs after loss of the C^Hg group. The driving force perhaps being the formation of a bond between C-l and C-4. The only small evidence that this could be happening comes from the spectrum of cis 4-t-butylcyclohexanol-(CD^)^-d^ [Fig. 14(b)]. The ions at m/e 100 and m/e 101 may be rationalized to correspond to the ion at m/e 99 in the cis nondeuterated isomer. The ion at m/e 101 being the one that has not lost the C-l hydrogen. Perhaps due to some isotope effect, which appears unusually large, the fragmentation reaction rate having slowed down so that the ion at m/e 101 can be detected in this case. The abundance of m/e 99 in the cis isomer 75 -H m/e 100 (Lyman a light source) is 29% of and the combined abundance of ions at m/e 100 and m/e 101 in cis 4-t-butylcyclohexanol-(CD„)„-d is (11.5% of Z 5 6 + 17.5% of E 5 6) giving a total of 29% 1^. From a partially deuterated molecule, i f a hydrogen is abstracted instead of a deuterium atom the ion would appear at m/e 99. An alternative explanation for the observation of both m/e 100 and m/e 101 ions in the spectrum of cis 4-t-butylcyclohexanol-(CXO Q-d n may be as follows. Perhaps the hydrogen atom on the hydroxyl group exchanges with one of the deuteriums on the tertiary butyl group and subsequently abstracts a deuterium atom and fragments as mentioned before. This mechanism would allow for the formation of ions at m/e 101. - 76 -However, i t is possible that some of the molecular ions fragment without any exchange occurring; this would then give rise to an ion at m/e 100. Thus both m/e 100 and m/e 101 would be expected to be present in the spectrum observed [Fig. 14(b)]. Exchange reactions between the hydroxyl group hydrogen and the hydrogens at C-3 and C-5 have been shown to occur in the low energy electron impact spectrum of cyclohexanol (64). In the present case, due to the proximity of the tertiary butyl group to the hydroxyl function i t may be possible that an exchange reaction i s also feasible. Metastable ions have been observed in the cis isomers (deuterated and non-deuterated) corresponding to this transition and are shown in Table III. - 77 -Table III. . Observed m/e Value for Ion m* Resulting from Metastable Transition 156 ->- 99 in Cis 4-t-Butylcyclohexanol and for the Corresponding Transition in the Cis Deuterated Alcohols m* m l m2 cis 4-trbutylcyclohexanol 62.8 156 99 cis 4-t-butylcyclohexanol-l-d^ 62.4 157 99 cis 4-t-butylcyclohexanol-2,2,6,6-d^ 66.3 160 103 cis 4-t-butylcyclohexanol-l,2,2,6,6-d,. 65.8 161 103 cis 4-t-butylcyclohexanol-(CD_),-d Q J j y 60.6 165 100 cis 4-t-butylcyclohexanol-(CD^)3-dg 61.8 165 101 Lyman a light source. The abstraction of a hydrogen from an alkyl side chain in cyclic systems has also been observed by other workers (65). Recently a communication (66) indicated that for cis 4-isopropylcyclohexanol the hydrogen lost with the hydroxyl group as water came mainly from the isopropyl group whereas in the trans isomer this was not the case. This conclusion was arrived at by deuterium labelling studies. trans cis - 78 -From high resolution measurements the ion at m/e 98 in the cis + isomer is found to be C^H^O . This ion most probably arises by loss of the tertiary butyl group followed by loss of a hydrogen. The hydrogens at C-3 (C-5) would be the most likely ones to be lost since a stable double bond could be formed. m/e 156 m/e 99 m/e 98 Deuterium studies verify the incorporation of hydrogens at C-l, C-2, and C-6 and loss of the tertiary butyl groups [Figs. 8(b), 10(b), 12(b) and 14(b)]. As mentioned before there i s a degeneracy at m/e 99 in cis 4~t-butylcyclohexanol-l-d^ [Fig. 8(b)] and at m/e 103 in cis 4-t-butylcyclohexanol-l,2,2,6,6-d^ [Fig. 12(b)], The ion at m/e 99 is also present in the trans isomer [Fig. 5(a) and 6(a)] although the abundance is relatively small compared to that of the cis isomer, especially in the spectra obtained with the Lyman a light source. A large fraction of these ions are probably formed by simple loss of the tertiary butyl group. However, one s t i l l observes in the spectra of the trans deuterated alcohols a peak analogous to that observed in the cis isomer, that i s , an ion at m/e 99 in trans 4-t-butylcyclohexanol-l-d^,[Fig. 8(a)],and at m/e 103 in trans 4-t-butylcyclohexanol-l,2,2,6,6-d,. [Fig. 12(a)]. A common mechanism may - 79 -therefore also exist in the formation of these ions. A ring opening mechanism would have to be postulated in this case. A-3. The ions at m/e 57 and m/e 56 The differences in the spectra obtained with the helium light source (Fig. 5) and with the Lyman a light source (Fig. 6) indicate that the higher energy requiring processes, for example simple cleavage of the tertiary butyl fragment resulting in an ion at m/e 57 predominates when higher ionizing energies are used. The increased relative abundance of ions in the spectra obtained using the Lyman a -f light source, that is [M-H^ O] ions at m/e 138 and the ion at m/e 99 agrees with the suggestion (54) that rearrangement reactions have lower frequency factors and low activation energies and thus dominate in spectra obtained with low ionizing energies. From high resolution measurements the ion at m/e 57 using the helium light source was found to be a doublet in the approximate ratio 1:9 comprising an oxygen containing fragment ion and a hydrocarbon fragment ion respectively. The former arises probably by a ring opening mechanism with loss of part of the ring as discussed by Budzikiewicz et a l . (34). Their mechanism is as follows: - 80 -m/e 57 This appears to be a major fragmentation pathway in other cyclic alcohols studied using electron impact for ionization (67,68). The deuterium labelled alcohols (Figs. 7, 9, and 11) in the present work do show an increase in abundance of ions at m/e 58 and m/e 59, however, no conclusive statement can be made. The hydrocarbon ion at m/e 57 is most probably the tertiary butyl fragment which would form a very stable tertiary carbonium ion. The inherent stability of this ion is perhaps one of the reasons for; i t s abundant formation. In the spectra of cis and trans 4-t-butylcyclo-hexanol- ( C D ^ ) ( F i g . 13) this ion appears at m/e 66 indicating that the fragment definitely consists of the tertiary butyl group. The appearance of an ion at m/e 65 in these deuterated alcohols is due partly to the presence of partially deuterated tertiary butyl groups (8 deuteriums incorporated). - 81 -The ion that appears at m/e 56 in both isomers of the non-deuterated and a l l of the deuterated compounds except for those with (CD^)^ groups in which case i t is present at m/e 64, arises either by loss cf a hydrogen radical from the tertiary butyl fragment or by some mechanism originating with the molecular ion that would abstract a proton from the tertiary butyl group and then fragment leaving the charge on the remaining portion of the tertiary butyl substituent. Different mechanisms may be operative in both isomers. For an identical mechanism one would have to postulate ring opening in the molecular ion before fragmentation. A-4. The ion at m/e 123 The ion at m/e 123 is present inboth cis and trans isomers (Figs. 5 and 6). The fragmentation reaction leading to this ion in the trans isomer has already been mentioned in connection with the [M-H^ O]"*" ion. The mechanism of formation in the cis isomer must necessarily be via a different pathway since there is no expected 1,4-elimination of water in this case, assuming the ring i s s t i l l intact. Therefore, a rationalization for the formation of this ion in the cis isomer may be, i n i t i a l loss of a methyl radical followed by water loss. The loss of a methyl radical is.seen in a l l the cis isomers with the loss of CD" in cis 4-t-butylcyclohexanol-(CD„)„-dn [Figs. o 3 J y 13(b) and 14(b)]. Incorporation of six hydrogens of the tertiary butyl group is indicated by the ion at m/e 129 in Figs. 13(b) and 14(b). Since the ion i s found to be a hydrocarbon by high resolution measurements, and both the a and g protons are incorporated in this •- 82 -fragment [Figs. 7(b), 8(b), 9(b) and 10(b)], water loss has to be postulated to occur by a 1,3-mechanism with possible rearrangements leading to an ion similar in structure to that described for the trans isomer, or by a 1,4-mechanism in which case ring opening would have to be postulated. A-5. The ions at m/e 80, 81, 82, and 83 The ions appearing at m/e 80, 81, 82, and 83 (Figs. 5 and 6) can be rationalized to arise as follows. From high resolution measurements these ions are found to be hydrocarbons. (i) Formation of the ion at m/e 80 One mechanism postulated for the formation of this ion in the traps isomer is as follows: - 83 -As mentioned previously the structure of the ion at m/e 123 i n the trans isomer is postulated to be like that of isopropylidenecyclohexane. The mass spectrum of this compound and those pf some of i t s deuterated derivatives have been studied by Wllhalm and Thomas (69) and the most abundant ion has been found to be due to loss of C^H*. The origin of this fragment is from the isopropylidene side chain together with one of the hydrogens from C-3 (C-5). The mechanism postulates the migration of the exocyclic double bond with two 1,3-hydrogen shifts. Djerassi et a l . (70) have also studied the mass spectra of several monoterpenoid hydrocarbons (similar ring systems) and have come to the same conclusions. The deuterium labelling results (Figs. 7, 9, 11, and 13) indicate that in the majority of these ions there i s retention of the a and $ hydrogens and loss of the tertiary butyl group. To explain the presence of this ion at m/e 80 in the cis isomer is more d i f f i c u l t since the ion at m/e 123 may have a different structure. Hoxrever, i t may be possible that by hydrogen shifts this ion loses C^ H- to give rise to the ion at m/e 80. The abundance of this ion in the cis isomer i s also larger than the trans isomer, (10% of E r, relative to 3% of Er/. for the spectra obtained with the Lyman a 56 56 light source, 7.5% of relative to 4.0% of E^ using the helium light source) thus indicating that more than one mechanism may be giving rise to this ion. Another possible precursor i s the ion at m/e 98 which by loss of water would give rise to an ion at m/e 80. In order to agree with the deuterium labelling results one would have to postulate that the hydrogen lost in the water molecule comes from either - 84 -C-4 or C-3 (C-5). Assuming the structure of the m/e 98 ion is as postulated, the following mechanism may be written. The ion most probably rearranges to form a more stable structure. Deuterium labelling at C-4 or C-3 (C-5) would possibly be able to cl a r i f y the situation. ( i i ) Formation of the ion at m/e 81 The formation of this ion in the trans isomer has already been discussed before in conneqtion with the structure of the [M-H^ O]"*" ion. It is possible that the ion rearranges and forms a cyclohexene type system rather than exist in the bicyclic form. m/e 98 m/e 80 m/e 138 m/e 81 - 85 -A similar mechanism can be postulated for the cis isomer where water loss possibly occurs by a 1,3-mechanism. However, this inter-mediate [M-^O]^ ion may be much more reactive than in the trans isomer and thus decomposes faster by loss of the tertiary butyl group. V e 156 . m/e 138 m / e 81 The smaller abundance of the m/e 81 ion in the cis isomer [helium light source, Fig. 5(b)] may be due to the fact that the molecular ions have other more favourable reaction sequences to undergo compared to the slower 1,3 loss of water. It is also possible that loss of the tertiary butyl group precedes loss of water. Deuterium labelling results (Figs. 7, 9, and 11) indicate that in the majority of these ions the deuteriums at the a and 6 positions are retained. Figure 13 also indicates that the majority of these ions have lost the tertiary butyl group. ( i i i ) Formation of the ion at m/e 82 This ion is probably formed by simple cleavage of both substituents followed by hydrogen shifts to form an ion similar to that formed.,on c ionization of cyclohexene. - 86 -m/e 156 m/e 139 m/e 82 Deuterium labelling at the a and g positions indicates incorporation of these protons in this fragment. The spectra of cis and trans 4-t-butylcyclohexanol-(CD^)^-dg (Fig. 13 and 14) show loss of the tertiary butyl group in the majority of these ions. However, a small peak is observed at m/e 85 which could correspond tq a fragment involving one of the methyl groups of the tertiary butyl chain. This would most probably arise via a ring opening mechanism. The subsequent decomposition of a major portion of the ions at m/e 82 may be by elimination of a methyl radical to form an ion at m/e 67 as follows: m/e 82 m/e 67 - 87 -Metastable ions corresponding to this transition are also observed in both isomers (helium light source). See Table IV. Table IV. Observed m/e Value for Ion m* Resulting from Metastable Transition 82 -> 67 in Both Cis and Trans 4-t-Butylcyclo-hexanol and for the Corresponding Transition in Their Deuterated Counterparts. m* m l m2 trans 4-ti-butylcyclohexanol 54.7 82 67 trans 4-t-butylcyclohexanol-2,2,6,6—d^ 55.4 86 69 cis 4-•t-butylcyclohexanol 54.7 82 67 cis 4-•t-butylcyclohexanolT-l*-d^ 55.7 83 68 cis 4--t-butylcyclohexanol-2,2,6,6-d^ 55.4 86 69 cis 4-•t-butylcyclohexanol-1,2,2,6,6-d,. 56.3 87 70 This type of decomposition is found to occur readily in cyclo-hexene type compounds (34). The deuterium labelling results (Figs. 7, 9, and 11) on the ion corresponding to m/e 67 indicate that hydrogep rearrangements are occurring and that loss of methyl radical is not via a single specific reaction. The follpwing discussion attempts to indicate, assuming there is no significant isotope effect, which ions would be expected to be formed in the deuterated derivatives i f the above mechanism is correct. On the assumption that ring opening occurs after hydrogen rearrangements in the ion corresponding to m/e 82. then for the alcohols - 88 -deuterated in the a position (Fig. 7), one would expect elimination as follows: m/e 68 Since the cyclohexene type structure is no longer symmetric i t can open either by breaking C-l - C-2 bond or C-3 - C-4 bond leading to different ions, Frpm the above analysis one would expect a larger abundance of ions at m/e 68 relative to m/e 67. This i s experimentally observed (Fig. 7). - 89 -For the tetradeuterated compounds (Fig. 9) one would expect the following (1,3-hydrogen shifts in the rearrangement of the ion corres-ponding to m/e 82): T V >D 2 x j j ? D HD m/e 86 j 1 3 J J 4 -CD H D 2 2 • HD i -CD D m/e 69 -CH: ...CH, H m/e 68 'CD, CHD + m/e 71 However, i f 1,2-hydrogen shifts are involved in the formation of the ion corresponding to m/e 82 then - 90 -Therefore one would expect ions at m/e 68, 69 and m/e 71 i f the ion corresponding to m/e 82 rearranges by 1,3-hydrogen shifts and at m/e 69, 70, and 71 i f the ion is formed by 1,2-hydrogen shifts. From Fig. 9 1,2-shifts appear to be preferred. For the compounds deuterated in both the a and 3 positions one can make the following analysis. If 1,3-hydrogen shifts are involved in the rearrangement of the ion corresponding to m/e 82 then, - 91 -HD 'CHD m/e 71 However, 1,2-hydrogen shifts in the rearrangement of the ion corres-ponding to m/e 82 w i l l lead to: - 92 Therefore one would expect ions at m/e 69, 70, 71 and 72 i f 1,3-hydrogen shifts are involved and at m/e 70 and 71 i f 1,2-shifts are involved. Experimentally from Figures 9 and 11 i t appears that both 1,2-and 1,3-hydrogen shifts may be operative in the rearrangement of the ions corresponding to m/e 82. The spectra obtained for cis and trans 4-t-butylcyclohexanol-(CD^^-d^ (Fig. 13) verifies that the tertiary butyl fragment is not involved in the ion at m/e 67. (iv) Formation of the ion at m/e 83 From high resolution measurements this ion is found to be C^H^^+. If the six carbons and ten hydrogens come from the ring, one more hydrogen has to be accounted for which most probably derives from the tertiary butyl side chain. A possible rationalization for the formation of this ion in both the isomers would involve the loss of the hydroxyl radical followed by ring opening and abstraction of a proton from the tertiary butyl substituent. Elimination of the stable C.H0 molecule would then • ' 4 8 lead to the ion at m/e 83. This would allow for the incorporation of the hydrogens at the a and g positions as observed from deuterium labelling (Figs. 7, 9 and 11). The incorporation of one deuterium atom from the deuterated tertiary butyl group is also evident from the ion at m/e 84 in Fig. 13. Contributions from other mechanisms leading to ions at m/e 80, 81, 82 and 83 most probably occur also. One reason for this stems from the fact that ions are observed in the deuterated isomers (Figs. 7, 9 and 11) below the normal group of ions corresponding to those being discussed. These do not just correspond to contributions from partially deuterated molecules. In Fig. 13 these appear at mass numbers above those for the main group of ions thus implying that the tertiary butyl group somehow plays a role in these mechanisms which most probably, occur via a ring opening mechanism. Finally, an ion which is present in larger abundance in the cis isomer (although minor compared to other peaks in the spectrum) appears at m/e 101. From deuterium labelling at the a and g positions, the spectra obtained (both light sources) indicate incorporation of these - 94 -hydrogens. The spectrum obtained for cis 4-t-butylcyclohexanol-(CD^)^-d^ also shows that the tertiary butyl group contributes to this ion, however, i t is d i f f i c u l t to rationalize a mechanism for i t s formation. A-6. Conclusions To conclude this section, i t appears that the fragmentation reactions leading to the ion at m/e 99 and m/e 138 in the cis and trans isomers respectively are sterically controlled. The availability of the tertiary hydrogen at C-4 in the trans isomer directs the fragmentation reaction leading to loss of water whereas in the cis isomer the large tertiary butyl group plays a prominant role. The ion at m/e 110 is not present in the spectrum of the cis isomer because the precursor ion (i.e. the [M-I^O]*1" ion) is postulated to be formed from the molecular ion by a 1,4-mechanism which is not possible in the case of the cis isomer. The spectra obtained with the helium light source have a much larger abundance of ions at lower m/e values due to the relatively large amount of energy imparted to the molecular ion on ionisation which leads to longer fragmentation sequences. The cleavage reaction leading to the formation of the tertiary butyl cation also predominates in spectra obtained with the higher ionising energy. The larger abundance of the m/e 138 ion in the spectrum of the trans isomer and that of the m/e 99 ion in the spectrum of the cis isomer obtained with the Lyman a light source agree with the suggestion that ions resulting from rearrangement reactions increase in abundance when lower ionizing energies are used. - 95 -UJ o z < Q z CD < Mill. 1,1, 6 0 SO tOO 120 m/e W 100 n < 11 . Ill m/e Fig. 5. Helium Light Source. Mass Spectra of (a) Trans 4-t-butylcyclohexanol (b) Cis 4-t-butylcyclohexanol . 100 / H / 1^  / (CH3)3c N Z ^ ^ 7 OH T H | XI0 il |IH ..{. 1 1 1 1 40 60 80 100 120 140 160 m/e 100 i 0H i 80 60 T H 40 • 20 0 il , i , J , -I. , 1 16 a o 60 80 100 120 140 160 m/e Fig. 6. Lyman a Light Source. Mass Spectra of (a) Trans 4-t-butylcyclohexanol (b) Cis 4-t-butylcyclohexanol. - 96 -100 80 60 40 UJ O 2 20 < I o m < UJ 100 > <C 80 _ l UJ V- 60 40 20 0 60 80 100 IZO 140 m/e 100 120 m/e xio OH i T H 1, 1 1, 1 J , 1 , .1. Fig. 7. Helium Light Source. Mass Spectra of (a) Trans 4-t-butylcyclohexanol-l-d^ (b) Cis 4^-t-butylcyclohexanol-l-d . Fig. 8. Lyman a Light Source. Mass Spectra of (a) Trans 4-t-butylcyclohexanol-l-d^ (b) Cis 4-t-butylcyclohexanol-l-d . - 97 -o Z 20 < o < Ul 100 > UJ °= so i i . (CH3)3C ill t tin 20 0 60 80 100 120 140 160 m/e Jj ICHjljC OH 60 80 100 m/e 140 160 Fig. 9. Helium Light Source. Mass Spectra of (a) Trans 4-t-butylcyclohexanol-2,2,6, (b) Cis 4-t-butylcyclohexanol-2,2,6,6-d • Fig. 10. Lyman a Light Source. Mass Spectra of (a) Trans 4-t-butylcyclohexanol-2,2,6,6-d (b) Cis 4-t-butylcyclohexanol-2,2,6,6-d. .' 0Q RELATIVE ABUNDANCE OP RELATIVE ABUNDANCE n u t - 1 D) PI 3 3 fl> I ft J> 8 I I rt r1 I p. OP 3 3-H rt i t n ^ ^ i -o o (_< o o 3 rt ET ro x 3 X 3 o I C/3 I-1 TJ ro NJ b r t i-f v« pi ON ON I - o &• ON Ml t-n I . Cb a4 w n H Ed H* 1-1 05 S) 3 .o cn I rt .P-I I CT rt 3 I OP rt CT 3" V! C rt I-1 3 3 tr1 n ^ c/: m o n o 3 H o o o ET t-> ro ro o . X ET pj ro 3 x O &) cn cn i ro NJ I—1 «* Q N> rt -» M ON t\3 fU ON ON O I - Mi a. o\ Ul I . Cu % 156 u < Q 100 80 60 40 20 H / / / H 1 XIO (0) ! , 1 1 ., ll..ll,J l , j l i L . i l l . . 1 ., . 1 1. , i 100 120 m/e Fig. 13. Helium Light Source. Mass Spectra of (a) Trans 4-t-butylcyclohexanol-(CDg)_-d (b) Cis 4-t-butylcyclohexanol-(CD^)^-Qg.^ 100 • 80 60 -40 -CE z 20 • < a z o =J CO 4 111 100 -1 > < 60 _J cc 60 • 40-20 0 (C0313C -1LL-, iklL 100 m/e OH r H . till. 1 ill , 1! lb) !l! I. .. 1 40 60 80 100 m/e 140 Fig. 14. Lyman a Light Source. Mass Spectra of (a) Trans 4~t-butylcyclohexanol-(CD3)o-d (b) Cis 4-t-butylcyclohexanol-(CD^-dg. - lpo -B. Cis and trans 4-t-butylcyclohexyl acetates A mass spectrometric study i n i t i a l l y carried out by Biemann (6) on a number of epimeric acetates indicated a relationship similar to that observed in the corresponding alcohols; that is the more crowded species in both the alcohols and the acetates gave rise to a smaller parent ion and a larger [M-H^ O]"^  ion or [M-HOAc]+ ion respectively. The spectra obtained for cis and trans 4-t-butylcyclohexyl acetates using the helium light source are shown in Fig. 15. The spectra are almost identical,and therefore, i t appears that both isomers fragment via the same pathway. A similar observation is made from the spectra obtained using the Lyman a light source (Fig. 16). At f i r s t glance no relationship seems to exist between the modes of loss of acetic acid and that of water in the corresponding alcohols (Section A-1). The base peak is at m/e 57 in the spectra obtained using the helium light source. The ion at m/e 138 is the base peak in the spectra obtained using the Lyman a light source. Once again, this illustrates that rearrangement reactions predominate in the spectra obtained with the lower ionizing energy. The following discussion w i l l attempt to explain the similarity observed in the spectra of the cis and trans acetates on the basis of their geometrical structure. The mode of formation of other specific ions in the spectra w i l l also be discussed. Scheme 3 indicates the major fragmentation routes involved in the decomposition of the acetates. - 101 -Scheme 3 + C 4 H 9 i / e 5 7 _ C 8 H 1 3 ° 2 ' < 0 H O-C-CH, 1+ H C(CH 3) 3 1,2 -CH3C00H m/e 83 C,,H10 m/e 82 /e 198 -CH, C10 H17 1,3 or 1,4 - C H 3 C O O H + C10 H18 /e 138 C2 H5°2 + + m /e 61 C6 H13°2 •CH3-m/e 117 C 9 H ! 5 + C rU 5 / m /e 123 m/r*. 67 Cis and trans 4-t-butylcyclohexyl acetates - 102 -B-l. The [M-HOAc] ion and the ion at m/e 61 A large number of the molecular ions in both isomers fragment by losing acetic acid. In order to determine which hydrogen is involved in this rearrangement reaction a number of deuterated 4-t-butylcyclohexyl acetates were prepared. Figures 19 and 20 show the spectra obtained for 4-t-butylcyclohexyl acetate-2,2,6,6-d4 using the helium light source and the Lyman a light source respectively. Those obtained for 4-t-butylcyclohexyl acetate-1,2,2,6,6-d,. are shown in Figs. 21 and 22. From these spectra one can conclude that the majority of the molecular ions lose one of the hydrogens from position two (or six) together with the acetate group, thus implying that 1,2 elimination is involved. This type of elimination has also been observed in cyclohexyl acetate (12). Other workers (34) using either 70 e T or 12 eV electrons came to the conclusion that 83% of CH^ CX^ D loss is observed in 1,2,2,6,6-d^-cyclohexyl acetate, whereas 17% of CH^ CO^ H i s ejected due to 1,3- or 1,4-elimination. A relative increase in the abundance of ions at m/e 142 and m/e 143 in Figs. 20 and 22 indicates that some of the ions eliminate via a 1,3 and/or 1,4 mechanism. A similar observation can be made for the spectra obtained with the helium light source (Figs. 19 and 21). However, in this case i t appears that a very small number of the molecular ions fragment via a 1,3 or a 1,4 mechanism. It is possible that the [M^-H0Ac]+ ion formed by this mechanism decomposes at a faster rate and therefore a major change in relative abundances is not observed. Two principle mechanisms may be considered to explain the identical spectra obtained for the two epimers. - 103 -(1) The ring opens after ionization but before any fragmentation reactions take place thus eliminating a l l differences between the isomers. (2) In some particular conformations i t i s possible for both isomers to lose acetic acid by the same mechanism to the same extent and therefore a l l other fragmentation reactions w i l l be similar. In order to elaborate on statement (2) consider the following analysis. If both the qis and the trans acetates are assumed to exist exclusively in the chair conformation, (the tertiary butyl group in an equatorial position) in the ionic state as is presumed to be in the ground state (Fig. 63) then, the trans isomer should eliminate twice as much acetic acid as the cis isomer because a l l four hydrogens at positions two and six are equally available. In the cis isomer only the two protons (H^, H^) cis to the acetate group are as close to the functional group as in the trans isomer. Experimentally both isomers are found to eliminate acetic acid to approximately the same extent. H 0 O-C-CH 3 (CH 3) 3Q 0 O-C-CH 3 trans cxs Figure 63. Chair conformations for trans and cis 4-t-butylcyclohexyl acetates. - 104 -Since there is no reason to believe that the ring w i l l assume a ri g i d conformation in the ionic state, therefore, i t is quite feasible that with the ring s t i l l intact the molecular ion can assume a variety of flexible conformations. The cis acetate group can in these conformations equally well abstract any of the four hydrogens at positions two and six (Fig. 64). The excess internal energy associated with the cis isomer may in some way also contribute to this process. This would thus lead to the same probability of abstraction Figure 64. A possible flexible conformation from which or can be abstracted in the cis isomer. as in the trans isomer. Furthermore, i t is possible that the trans isomer may also assume a variety of flexible conformations. The mechanism of loss of acetic acid can be looked upon as a migration of the hydrogen to the carbonyl oxygen. This type of rationalization involving a six-membered transition state was f i r s t proposed by McLafferty (71,72). The transfer of a y-hydrogen is usually involved. The positive charge is stabilized on the acid fragment only i f i t abstracts another hydrogen and forms the protonated form of the acid. This type of ion has been observed previously in - 105 -m/e 198 m/e 138 acetates (73). In the present work, ions at m/e 61 in the non-deuterated acetates (Figs. 15 and 16) correspond to the protonated form of acetic a:id. An analysis of this peak in the deuterated acetates leads to the following conclusions. The spectra obtained with the helium light source w i l l be considered mainly because the relative abundance of the ions corresponding to m/e 61 is quite significant compared to that obtained with the Lyman a light source. In the spectra of cis and trans 4-t-butylcyclohexyl acetate-l-d^ (Fig. 17) a small peak is observed at m/e 62, the majority s t i l l appearing at m/e 61. This implies that after the i n i t i a l abstraction of a proton from either positions two or six by the acetate group the acid moiety then abstracts a proton that comes mainly from the other ring hydrogens, besides the proton at C-l, or from the tertiary butyl group. The same can be said i f the i n i t i a l abstraction is by a 1,3 or 1,4 process. In the spectra of cis and trans 4-t-butylcyclohexyl acetate-2,2,6,6-d^ (Fig. 19) ions are present at m/e 61 and m/e 62 with approximately equal abundances. The ion at m/e 62 arises either by i n i t i a l abstraction, - 106 -from the 2 (or 6) position followed by one from position 4 or 3 (5) or the tertiary butyl group. The other possible mode of formation is by i n i t i a l abstraction from 4 or 3 (5) positions followed by one from the 2 (or 6) position. The ion at m/e 61 is most probably due only to 1,3 or 1,4 elimination with subsequent abstraction of a proton from 4 or 3 (5) positions by the acid function. The above analysis does not imply that the ring is intact after the f i r s t abstraction. It is possible that the ring opens and as such makes the second abstraction at random. A similar analysis can be made of the spectra obtained for cis and trans 4-t-butylcyclohexyl acetate-l,2,2,6,6-d^ (Fig. 21). In this case there is a small increase in the abundance of m/e 63 corresponding to a similar one observed (at m/e 62) in 4-t-butylcyclohexyl acetate-l-d^ The fact that an ion is observed at m/e 61 in a l l the derivatives deuterated at the 3 positions implies that a small amount of elimination of acetic acid does go via 1,3 or 1,4 mechanism. The i n i t i a l abstraction reaction in the cis isomer is probably only by a 1,3 mechanism assuming the ring i s intact, whereas in the trans isomer both 1,3 and 1,4 mechanisms are possible. B-2. The ion at m/e 123 Another im in the spectra of cis and trans 4-t-butylcyclohexyl acetate (Fig.s 15 and 16) which is most probably not a fragmentation product of the sequence beginning with 1,2 elimination is at m/e 123. This ion is found to be CnH1,-+ by high resolution measurements. From y i j the deuterium labelling results, especially those obtained using the - 107 -helium light source (Figs. 17, 19, 21 and 23) the following observations can be made. The a and g protons are incorporated in this fragment ion and six protons from the tertiary butyl group are also involved in this ion. This would, therefore, suggest that mechanisms for the formation of this ion are similar to those postulated for cis and trans 4-t-butylcyclohexanols. B-3. The ion at m/e 117 Another ion which i s common to both isomers is at m/e 117 (Fig. 15 and 16). From high resolution measurements this ion was found to be £(^-±'3^2 '' D e u t e r i - u m labelling results (both light sources) indicate the incorporation of one of the hydrogens from C-2 (or C-6) (Figs. 19, 20, 21, and 22). Furthermore, in the spectra obtained for cis and trans 4-t-butylcyclohexyl acetate-(CD„)_-d (Figs. 23 and 24) the ion now appears at m/e 126 indicating that a l l the hydrogens of the tertiary butyl group are involved. Therefore, a mechanism for i t s formation would have to be postulated which would be consistent with the above experimental observations. A rearrangement of some sort is probably involved since the relative abundance of this ion increases with lower ionizing voltages. A possible rationalization is as follows: - 108 -The presence of the acetyl group which contains two heteroatoms can lead to a double abstraction reaction. Reactions of this type have been postulated to take place in esters, amides, carbonates and phosphates (59). The ion at m/e 61, previously discussed, in the present case arises due to a double rearrangement reaction. However, in the formation of the ion at m/e 117 hydrogen abstraction would have to be followed by migration of the tertiary butyl group as suggested in the scheme. Alkyl and aryl migrations have been observed previously in mass spectra (74,75). Although the migrating group is large in this case the rearrangement may s t i l l be possible. Ring opening would have to take place at some stage in order to account for the presence of the ion in both isomers, unless there is some way in which the tertiary butyl group can migrate to the acetate substituent with the ring intact in both isomers. The relative abundance of this ion (both light sources) i s quite small compared to other ions in the spectra thus implying that the fragmentation route i s a minor one. - 109 -B-4. The ions at m/e 80, 81, 82, and 83. The ions at m/e 80, 81, 82, and 83 are probably formed by mechanisms similar to those discussed for cis and trans 4-t-butylcyclohexanols. (i) The ion at m/e 80 The precursor for the ion at m/e 80 is most probably the [M-H0Ac]+ ion. Several metastable ions corresponding to this transition are observed as indicated in Table V, Table V. Observed m/e Value for Ion m* Resulting from Metastable Transition 138 -> 80 in Both Cis and Trans 4-t-Butylcyclo-hexyl Acetates and for the Corresponding Transition in Their Deuterated Analogues. m* m* m l m2 trans 4--t^butylcyclohexyl acetate 46.3 46.3 138 80 trans 4--t-butylcyclohexyl acetatel-l-d^ 47.2 47.2 139 81 trans 4--t-butylcyclohexyl acetate-1,2,2,6,6-d^ 49.6 — 142 84 trans cis 4^  4-•t--t-butylcyclohexyl acetate-(CD 3) 3-d 9 -butylcyclohexyl acetate 43.5 46.3 43.5 46.3 147 138 80 80 cis 4-•t--butylcyclohexyl acetate-1-d^ 47.2 — 139 81 cis 4-•t--butylcyclohexyl acetate-2,2,6,6-d4 48.8 — 141 83 cis 4--t--butylcyclohexyl acetate-1,2,2,6,6-d^ 49.6 — 142 84 cis 4-•t--butylcyclohexyl acetate-(CD 3) 3-d 9 43.5 43.5 147 80 Helium light source; Lyman a light source - 110 -A possible fragmentation scheme for the formation of this ion is as follows: m/e 80 The loss of the tertiary butyl group and a proton i s most probably by a concerted mechanism. The proton lost comes from the 3 (5) positions of the ring. However, another mechanism may also be operative in forming the ion at m/e 80. Evidence for this comes from the fact that in the deuterated acetates, ions at mass numbers below those corresponding to the mechanism discussed as present. These ions are not simply due to incomplete deuteration. These alternate fragmentation routes are probably via ring opening mechanisms. (i i ) The ion at m/e 81 The ion at m/e 81 is probably formed mainly by loss of the + tertiary butyl group from the [M-HOAc] ion. - I l l -( i i i ) The i o n at m/e 82 The mechanism of formation of the i o n at m/e 82 i s probably s i m i l a r to that discussed i n the case of the 4-t- b u t y l c y c l o h e x a n o l s . The subsequent decomposition of t h i s i o n i s by the l o s s of a methyl r a d i c a l to form the i o n at m/e 67. Metastable ions corresponding to t h i s t r a n s i t i o n are observed i n both c i s and trans acetates and some of t h e i r deuterated counterparts are shown i n Table VI (He l i g h t source). Table VI. Observed m/e Value f o r Ion m* R e s u l t i n g from Metastable T r a n s i t i o n 82 ->• 67 i n Both Cis and Trans 4 - t - B u t y l c y c l o h e x y l Acetates and f o r the Corresponding T r a n s i t i o n i n Some of the Deuterated Counterparts. m* m l m 2 trans 4 - t - b u t y l c y c l o h e x y l acetate 54.7 82 67 trans 4 - t - b u t y l c y c l o h e x y l a c e t a t e - l - d ^ 55.7 83 68 trans 4 - t - b u t y l c y c l o h e x y l acetate-(CD^)^-d^ 54.7 82 67 c i s 4 - t - b u t y l c y c l o h e x y l acetate 54.7 82 67 c i s 4 - t - b u t y l c y c l o h e x y l a c e t a t e - l - d ^ 55.7 83 68 c i s 4 - t - b u t y l c y c l o h e x y l acetate-(CD^)^-d^ 54.7 82 67 A s i m i l a r a n a l y s i s f o r t h i s decomposition can be made as i n the case of the a l c o h o l s i n the previous s e c t i o n [Section A-5 ( i i i ) ] . - 112 -( i v ) The i o n at m/e 83 The i o n at m/e 83 i s probably formed by a mechanism analogous to that discussed i n the case of the a l c o h o l s . The appearance of an io n at m/e 84 i n the sp e c t r a of c i s and trans 4 - t - b u t y l c y c l o h e x y l acetate—(CD«)„—d_ f u r t h e r supports the p o s s i b i l i t y that the mechanism i s probable. However, as mentioned before i n the case of the a l c o h o l s other modes of fragmentation do seem to p l a y a r o l e i n the formation of these i o n s . The only d i f f e r e n c e t h a t e x i s t s i n the s p e c t r a of the two isom e r i c acetates i s that the i o n at m/e 141 i s absent i n the c i s isomer ( F i g s . 15 and 16). This i s a very s m a l l peak and th e r e f o r e not considered to be a major d i f f e r e n c e . This d i f f e r e n c e i s maintained i n the s p e c t r a of the deuterated acetates except f o r c i s and trans 4-t-b u t y l c y c l o h e x y l a c e t a t e - ( C D 3 ) 3 - d g , where i t i s d i f f i c u l t to t e l l as ions are present at the same mass numbers due to p a r t i a l l y deuterated molecules. This i o n i s formed i n the trans isomer by the l o s s of the t e r t i a r y b u t y l group. The ions at m/e 142 and me/ 143 correspond to the l o s s of 56 and 55 mass u n i t s r e s p e c t i v e l y . These l a t t e r ions are observed i n the s p e c t r a of the c i s isomer. I t i s p o s s i b l e that due to s t e r i c i n t e r a c t i o n i n the c i s isomer a b s t r a c t i o n from the t e r t i a r y b u t y l group i s a much more f e a s i b l e process and th e r e f o r e no l o s s corresponding to m/e 57 i s observed. B-5. Conclusions In conclusion the replacement of the hyd r o x y l f u n c t i o n by the acetate group causes q u i t e a r a d i c a l change i n the mode of decomposition of the isomers. The a c e t y l f u n c t i o n i s an e l e c t r o n a t t r a c t i n g group and thus l o s s of a c e t i c a c i d becomes more probable r e s u l t i n g i n a - 113 -180 200 F i g . 15. Helium L i g h t Source. Mass Spectra of (a) Trans 4 - t - b u t y l c y c l o h e x y l acetate (b) C i s 4 - t - b u t y l c y c l o h e x y l a c e t a t e . / / H \ / 1 <CH»>»e s ^ ^ ^ y <»« 1 1 T H 1 (01 1 xio 1 j 1 ll. . , . 1.. . I i i 100 120 m/e • 40 OAc | / / A r -30 T H 1 1 •20 (Dl 1 XIO 1 1 •10 J 1 . ill. 1 1 11. I I 0 60 100 120 m/e 140 160 F i g . 16. Lyman a L i g h t Source. Mass Spectra of (a) Trans 4 - t - b u t y l c y c l o h e x y l acetate (b) C i s 4 - t - b u t y l c y c l o h e x y l acetate . - 114 -Fig. 17. Helium Light Source. Mass Spectra of (a) Trans 4-t-butylcyclohexyl acetate-l-d^ (b) Cis 4-t-butylcyclohexyl acetate-l-d . / • 50 / <0 D 7 / i 30 1 H 1 xio • ZO (a) 1 1 10 - X , i J. 1 , J ' • 0 80 100 120 140 160 m/e / OAc | / / 1 H 1 lb) J ,1 ,, , ill, , , , 1 , • , l jxio 80 100 120 m/e 140 160 Fig. 18. Lyman q Light Source. Mass Spectra of (a) Trans 4-t-butylcyclohexyl acetate-l-d^ (b) Cis 4-t-butylcyclohexyl acetate-l-d . 09 RELATIVE ABUNDANCE ro cr (U o • o H t-1 i-i cn pi ^ 3 4> i cn 3 t rt -P- P 1 cr 1 rt r 1 C 1 H-rt cr CM <^ C IT M rt rt O ^ 1—1 CO o O o t—1 ••<; c o n r< n fD o ro X ••<: ro PJ i—1 o cn (D rt o CO CO rt rt ro a> 93 o 1 rt rt ft) l-t J 1 IO tO J <* o IO Ml <j i OQ RELATIVE ABUNDANCE N M cr PJ ^ ' ^ ' • n t-3 H ro CO P> •C- cn c 1 3 rt •P~ 1 1 r 1 cr rt H» C 1 OQ rt a 4 ET •<! C rt h-> rt n CO v! o o n c n o n o rr i—1 ro ro o • X rr V! ro S i-» X (U CO PJ M CD O ro PJ CO rt O PJ ro ro rt rt o ro (U rt rt H ro PJ i ro ro O o> 1 ON 1 • a. - 116 -/ / / 'one 1 1 H 1 .1 , i i I J I (0) 1. .,. 1 , | XIO 1 1 1, II. 1 1 2 "0 60 80 100 120 140 160 180 200 5 m/e « Oh / / / \ Y * H • XIO 11 1 1 , J , 1 (b) 1. ... .. 1. i „ .. 1, II 1 1 40 60 80 100 120 140 160 ISO 200 m/e Fig. 21. Helium Light Source. Mass Spectra of (a) Trans 4-t-butylcyclohexyl acetate-1,2,2,6,6-d (b) Cis 4-t-butylcyclohexyl acetate-1,2,2,6,6-d 100 80 60 40 U l O Z 20 < O § 0 m < LU 100 > • / 0 j 1 °2 H I«I 1 XIO .1, . 1 Hi. 1. •• • L_lii_, , , , fl < 80 ^ 60 40 20 0 80 100 120 m/e 140 160 120 m/e IS in Fig. 22. Lyman a Light Source. Mass Spectra of (a) Trans 4-t-butylcyclohexyl acetate-1,2,2,6,6-d (b) Cis 4-t-butylcyclohexyl acetate-1,2,2,6,6-d . 00 RELATIVE ABUNDANCE 00 RELATIVE ABUNDANCE —^\ K J 0! *—' • o i-i cn 0) 3 3 03 -> cn 3 1 rt -O S 1 cr I rt t-<  1 rt cr oo 3 pr t-> rt rt n V! cn n n o VJ 3 O o l-i PT h-1 n (D O ro X cr • CD h-1 X S 03 03 cn O cn (D f» rt n en CU CD rt rt ro n> 0> o 1 ro rt >-i i 03 a ^—s G J n o a l-h U3 U ) 1 s^ CLU) I PL —^  N3 cr 0) *— V-/ • n H PC H- f-S ro cn 03 i—1 3 H-J > cn 3 I g rt -i> 1 1 t-1 cr rt 3 1 oo rt a 4 pr <^ 3 rt M rt O CO •<! 1—1 O o n 3 H"<! H O n O P* ro ro o • X pr ro h-> X QJ CO 03 h-1 CO o ro 03 CO rt n 93 ro ro rt rt o ro 03 rt 1 rt H ro 03 n i —s O n l-t> a UJ LO 1 CLOJ 1 • PL. 3 - 118 -very small molecular ion. Abstraction of the hydrogens at C-2 and C-6 is feasible due to the fact that the acetate group is much larger and because of the presence of the carbonyl group. This leads to loss of acetic acid by a 1,2-mechanism. The introduction of this fragmenta-tion mode explains the similarity in the spectra of the two isomers. Loss by a 1,3 and/or 1,4 mechanism i s also operative but to a minor extent.' The presence of the acetate functional group which contains two heteroatoms cans also lead to double abstraction reactions. The ion at m/e 61 arises from a double hydrogen abstraction reaction whereas the ion at m/e 117 is considered to arise by the abstraction of a hydrogen atom followed by abstraction of the tertiary butyl group. C. Cis and trans 4-t-butylcyclohexyl methyl ether s Many studies have been done on aliphatic ethers using electron impact for ionization (34,76,77). Some similarity in the fragmentation behaviour has been found between these ethers and the related aliphatic alcohols. However cyclic ethers have not been studied in as much detail. Recently methyl cyclohexyl ether and i t s deuterated analogues have been looked at by Klein and Smith (78) and these workers have arrived at the conclusion that the major decomposition modes follow paths parallel to those reported for cyclohexanol. In the present work cis and trans 4-t-butylcyclohexyl methyl ether and some of i t s deuterated derivatives were synthesized and the mass spectra obtained using photon impact. An attempt was made to determine i f these ethers fragment in an analogous fashion to the 4-t-butylcyclo-- 119 -hexanols, the isomers of which were found to undergo different decomposition modes (Section A). The spectra obtained for cis and trans 4-t-butylcyclohexyl methyl ether using the helium light source are shown in Fig. 25. In general the following observations can be made. 1. The parent ion is smaller in the trans isomer (2.7% of T.^) compared to the cis isomer (7.3% of • 2. The [M-MeOH]+ ion i s much larger in the trans isomer (18.8% of compared to 4.9% of in the cis isomer. 3. The ion at m/e 110 is significant in the spectra of the trans isomer. 4. The ions at m/e 114 and m/e 115 are of relatively large abundance in the cis isomer. 5. The base peaks are not at the same m/e value in the two isomers. Similar observations can be made from the spectra obtained using the Lyman a light source (Fig. 26) and for the deuterated analogues taking into account the shifts due to isotope incorporation in certain fragments (Figs. 27, 28, 29, 30, 31, 32, 33, and 34). As in the case of the alcohols i t is most probably one of the lone pair electrons on the oxygen atom that i s lost in the ionization process thus localizing the positive charge on the oxygen atom. The differences observed in the spectra of the individual isomers using both light sources, once again, indicate that the ions at m/e 138, m/e 114 and m/e 115 are most probably formed by rearrangement reactions. As mentioned previously rearrangement ions predominate in spectra obtained with lo" "ionizing energies. - 120 -The following discussion w i l l be divided into five main sections. 1. The mode of formation of the [M-Me0H]+ ion in both the cis and trans isomers. 2. The ion at m/e 123. 3. A discussion of the possible mechanisms leading to the ions between m/e 112 and m/e 116. 4. ' The ions at m/e 80, 81, 82, and 83. 5. The ions at m/e 71, 67, 58, and 57. Schemes 4 and 5 attempt to il l u s t r a t e in general the fragmentation routes taken by trans and cis 4-t-butylcyclohexyl methyl ether respectively. C-l. The [M-MeOH]+ ion The values obtained for [M-MeOH]+/M+ ratio from the spectra of both deuterated and undeuterated cis and trans methyl ethers (both light sources) are shown in Table VII. Table VII. [M-Me0H]+/M+ Ratio for Cis and Trans 4-t-Butylcyclohexyl Methyl Ethers and Deuterated Analogues (both light sources). + +a + +b [M-rMeOH] /M [M-MeOH] /M trans 4-t-butylcyclohexyl methyl ether 7.35 7.8 trans 4-t-butylcyclohexyl methyl ether- 7.0 8.3 l - d x trans 4-t-butylcyclohexyl methyl ether- 9.35 8.4 2,2,6,6-d4 trans 4-t-butylcyclohexyl methyl ether- 9.1 7.7 l,2,2,6,6-d5 trans 4-t-butylcyclohexyl methyl ether- 10.4 8.0 (CD 3) 3-d 9 - 121 -Table VII (Continued) cis 4-t-butylcyclohexyl methyl ether cis 4-t-butylcyclohexyl methyl ether L - d l cis 4-t-butylcyclohexyl methyl ether 2,2,6 »6-d4 cis 4-t-butylcyclohexyl methyl ether 1,2,2 ,6,6-d,. cis 4-t-butylcyclohexyl methyl ether (CD 3) 3-d 9 a Helium light source; ^ Lyman a light source Although the difference in the ratio between the two isomers is not as large as in the case of cis and trans 4-t-butylcyclohexanol the same general trend is apparent, i.e., a larger amount of methanol is lost in the trans isomer which also has the smaller parent ion. The loss of methanol in the trans isomer most probably takes place mainly via a 1,4 mechanism paralleling that observed in trans 4-t-butyl-cyclohexanol. The ion at m/e 110 is indicative that a least some of the molecular ions fragment via this mechanism. The ion at m/e 110, as in the alcohol probably has the ion at m/e 138 as precursor. /e 170 m/e 138 m/e 110 [M-MeOH] /M 0.68 0.72 0. 71 0.71 0.74 [M-Me0H]+/M 0.68 0.65 0.66 0.58 0.69 - 122 -Scheme 4 + - C7 H13 0' C 4 H 9 <  H OCH + " C H3 > C 1 nH 1 s"i" > CnH, c + -CH„0H 10 18 ^ 9 15 l/e 138 -C 2H 4 m/e 123 -C3H-+ C6 H8 m/e 80 m/e 67 m/e 71 Trans 4 - t - b u t y l c y c l o h e x y l methyl ether - 123 -Scheme 5 C3 H6° m/e 58 C 7H 1 50 m/e 115 H OCH„ H C(CH 3) 3 1,3 -CH C10 H18^ -CH OH 3 m/e 138 C6 H10 m/e 82 -CH* V C5 H7 + m/e 67_ Cis 4-t-butylcyclohexyl methyl ether C4 H9 + C 7H 1 30 m/e 113 \-CH3OH -H C ?H 1 20t m/e 112 C6 H9 m/e 81 C4H70 m/e 71 - 124 -Deuterium labelling confirmed that no loss of methanol takes place by a 1,2 mechanism (Figs. 29, 30, 31, and 32). Furthermore the number of deuterium atoms incorporated in the ion corresponding to m/e 110 in the various labelled trans isomers (Figs. 27, 29, 31, and 33) indicates that the ion structure postulated is quite feasible. Loss of methanol in the trans isomer could equally well occur by a 1,3 mechanism. If this pathway is parallel to that observed in unsubstituted cyclohexanol then ring opening may have to precede this loss as suggested by M.M. Green et a l . (2). The observation that loss of methanol in the trans isomer is not as abundant as the loss of water in the trans alcohol (Section A-l) is due to the fact that the methyl group on the ether oxygen is more capable of stabilizing the positive charge on the heteroatom due to i t s inductive effect. This would lead to a lowering of the probability for this rearrangement reaction. In cis 4-t-butylcyclohexyl methyl ether [Figs. 25(b) and 26(b)] a significant ion corresponding to loss of methanol is observed, in contrast to cis 4-t-butylcyclohexanol where a relatively small [M-H^O^ion is observed [Figs. 5(b) and 6(b)]. This may imply, assuming the ring is s t i l l intact, that 1,3 loss of methanol has become a more favourable elimination. Perhaps the increase in steric hindrance between the methyl group on the oxygen and the axial hydrogens on C-3 (C-5) leads to a larger amount of fragmentation due to release of this steric strain. In this case i t would appear that the steric effect overrides the inductive effect of the methyl group. From electron impact studies the proton lost in the formation of - 125 -methanol in cyclohexyl methyl ether was found to originate mainly from the 3(5) positions (66%), 23% from C-4 and 8% from the C-2 (C-6) positions (78). C-2. The ion at m/e 123 The ions at m/e 123 in both isomers probably arise by similar mechanisms as indicated for the alcohols (Section A-4), loss of methanol taking place instead of water. Deuterium labelling on the ethers (Figs. 27, 29, 31 and 33) verify the incorporation of the a, and 3 protons and six protons of the tertiary butyl group. C-3. The ions between m/e 112 and m/e 116 A very significant difference observed in the spectra between the cis and trans isomers (using both light sources) is the set of ions between m/e 112 and m/e 116 (Figs. 25 and 26). These ions are of very low intensity in the trans isomer, the ion at m/e 112 being absent. The ion at m/e 112 in the cis isomer, found to be C^H^o"*" by high resolution, is probably analogous to the m/e 98 ion observed in the cis alcohol. This ion most probably arises by loss of the tertiary butyl group together with a hydrogen radical. This loss may be concerted or the radical may be lost prior to the loss of tertiary butyl groups. Deuterium labelling [Figs. 27(b), 28(b), 29(b), 30(b), 31(b), and 32(b)] indicates that the a and 3 protons are retained in this ion. Figures 33(b) and 34(b) show the loss of the tertiary butyl group. This implies that the hydrogen lost originates from either the four or three (five) position of the ring. The 3 (or 5) - 126 -+• +• +r m/e 170 m/e 113 m/e 112 position seems more favourable since a stable double bond can be formed. Loss of. the tertiary butyl group results in an ion at m/e 113. This ion is the largest of the group in the trans isomer but very small relative to m/e 114 and m/e 115 in the cis isomer. The ion at m/e 114 in the cis isomer is most probably formed via a rearrangement reaction. High resolution measurements indicate that i t s composition is C^ H^ o"*". Thus loss of 56 mass units occurs or a C^Hg fragment is lost. Assuming that the ring is s t i l l intact, the molecular ion can f l i p into a flexible conformation which would bring the methoxyl and the tertiary butyl group very close. Abstraction of a hydrogen can occur from the tertiary butyl group as suggested in the case of the cis alcohol when discussing the m/e 99 ion. A rationalization for this decomposition is as follows. - 127 -Deuterium labelling at the a and B positions indicates these hydrogens are retained in this ion [Figs. 27(b), 28(b), 29(b), 30(b), 31(b), and 32(b)]. The spectrum obtained for cis 4-t-butylcyclohexyl methyl ether-(CD,),-d Q (helium light source) shows a f a i r number of ions due to partially deuterated tertiary butyl groups [Fig. 33(b)]. However, i t is s t i l l possible to pick out the ion at m/e 115 as corresponding to the ion at m/e 114 in the unlabelled cis isomer. Similarly for the spectrum obtained using the Lyman a light source [Fig. 34(b)]. The ions present at m/e 114 in these spectra are due most lik e l y to an abstraction of a proton from the partially deuterated tertiary butyl group. To explain the presence of the m/e 115 ion in the spectrum of cis 4-t-butylcyclohexyl methyl ether one would have to postulate some sort of "double rearrangement" mechanism. This ion is found by high + resolution measurements to be C^H^O , thus losing 55 mass units from the molecular ion. Deuterium labelling results [Figs. 27(b), 28(b), 29(b), 30(b), 31(b), and 32(b)] at the a and B positions of the ring indicates that these protons are retained in this fragment ion. The - 128 -spectrum for cis 4-t-butylcyclohexyl methyl ether-(CD^^-d^ [Lyman a light source, Fig. 34(b)] shows the presence of an ion at m/e 117 which would arise by abstraction of two deuterium atoms from the tertiary butyl group. The ion at m/e 116 in this spectrum is formed most probably by abstraction of one deuterium and one hydrogen atom from the partially deuterated tertiary butyl group. Abstraction of two protons would give rise to an ion at m/e 115 which in this case would cause a degeneracy at this mass number. Therefore, a fragmentation mechanism leading to the ion at m/e 115 may involve abstraction of a hydrogen radical from the tertiary butyl group by the reactive methoxyl group followed by cleavage of the ring. This would give rise to another reactive radical which may abstract another hydrogen from the tertiary butyl group before loss of the fragment C^ H^  (remaining portion of the tertiary butyl group) occurs. Ring opening would have to take place at some point in the scheme. It is possible that in the formation of both m/e 114 and m/e 115 ring opening occurs after ionization but prior to fragmentation in some cases. This would also account for the presence of these ions in the trans isomer. Thus, i t is possible that more .than one mode of formation of these ions is operative. The ring opening mechanism prior to any fragmentation, perhaps, being solely responsible for the formation of these ions in the trans isomer where the desired stereochemical arrangement for the operation of the other mechanism is not possible. The relatively small intensities of these ions in the trans isomer is probably due to the fact that other faster and more favourable reaction pathways are available to the molecular ion. - 129 -Some metastable ions observed corresponding to the transition 170 -> 115 are shown in Table VIII. Table VIII. Observed m/e Value for the Ion m* Resulting from Metastable Transition 170 -»• 115 in Cis 4-t-Butylcyclohexyl Methyl Ether and the Corresponding Transition in the Deuterated Analogues. j.a .b m* m* m^  m cis 4-rt-butylcyclohexyl methyl ether 77.8 77.8 170 115 cis 4-t-butylcyclohexyl methyl ether-1-d^ •— 78.7 171 116 cis 4-t-butylcyclohexyl methyl ether-2,2,6,6-d. — 81.4 174 119 Helium light source; Lyman a light source The larger relative abundance of the m/e 115 ion compared to the m/e 114 ion in the spectrum obtained with the Lyman a light source suggests that the formation of the "double rearrangement" ion is more feasible in molecular ions with low internal energy in agreement with the observation made by others (56). C-4. The ions at m/e 80, 81, 82, and 83 The large intensity of the ions between m/e 80 and m/e 84 in the spectrum obtained with the helium light source (Fig. 25) indicates that these are products of ions of high i n i t i a l energy content. Since these ions are more abundant in the spectra obtained with the - 130 -helium light source the following discussion w i l l centre around these spectra. (i) The ion at m/e 80 The ion at m/e 80 is larger in the cis isomer compared to that in the trans isomer (4.2% of E,, relative to 2.1% of E,,) . In the trans 41 41 isomer the formation of this ion may be by loss of C^&j from the ion at m/e 123 as discussed for the trans alcohol (Section A-4.). In the cis isomer i t may also have the ion at m/e 123 as precursor, however, in this case the structure of this ion would be different from that in the trans isomer, as mentioned before. Furthermore, the ion at m/e 112 in the cis isomer can also decompose by loss of methanol to give rise to an ion at m/e 80 as follows: m/e 170 m/e 112 m/e 80 This ion probably rearranges to form a more stable structure. From the deuterium labelling results i t appears that in the majority of these ions the q and g protons are retained and that the tertiary butyl group is lost. ( i i ) The ion at m/e 81 The ion at m/e 81 is most probably formed by mechanisms as indicated for the 4-t-butylcyclohexanols eliminating methanol instead of water (Section A-5 ( i i ) ] . - 131 -( i i i ) The ion at m/e 82 Two main fragmentation routes may be postulated for the formation of the ion at m/e 82 as follows: H O-CH, -OCH, H " C4 H9 H drogen hif tsT hy  s m/e 170 l/e 139 i/e 82 H H +6-CH, - C H 2 = C ( C H 3 ) 2 -CH 3 0 H hydroger s h x i t s H m/e 114 m/e 82 Route (1) can be taken by either isomer whereas route (2) w i l l probably be more prominent in the cis isomer. (iv) The ion at m/e 83 The ion at m/e 83 is formed either by a mechanism as suggested for the alcohols losing the methoxyl group as the f i r s t step or simply by loss of methanol from the ion at m/e 115. The second mode of formation would be prevalent most probably only in the cis isomer. The a and 8 protons are retained in this fragment ion as determined - 132 -from deuterium labelling (Figs. 27, 29, and 31). The spectrum of cis 4-t-butylcyclohexyl methyl ether -(CD_)_-d_ [Fig. 33(b)] shows an ion j j y at m/e 84. This is probably due to the abstraction of two deuteriums in the formation of m/e 115 with subsequent loss of one as MeOD, or due to abstraction of a deuterium from the tertiary butyl group by a mechanism as suggested for the alcohols [Section A-l (iv)]. However, due to the complicating effect of partial deuteration in the cis-d^ isomer one would expect to see an ion at m/e 83 as well. As mentioned previously both for the alcohols and the acetates i t appears that these ion can also be formed by other minor fragmentation routes involving the tertiary butyl group. The same can be said for the 4-t-butylcyclohexyl methyl ethers. C-5. The ions at m/e 71, 67, 58, and 57 The ion at m/e 71 (Fig. 25) is due to 3 cleavage of the ring. This type of decomposition is known to occur readily under electron impact conditions, where ions have been observed at m/e 57 in cyclohexanol (34) and at m/e 71 in cyclohexyl methyl ether (78). The mechanism postulated by Djerassi et a l . (34) may be applied to the present system as follows: m/e 170 m/e 71 - 133 -The driving force for the above fragmentation route i s thought to be the formation of the a l l y l i c ion at m/e 71. From the present deuterium labelling results the a proton is found to be incorporated in the fragment ion (Figs. 27 and 31). However, only one of the g protons (Figs. 29 and 31) is involved. High resolution measurements indicate that the ion is C,H-,0+. The spectrum obtained for trans 4-t-4 7 butylcyclohexyl methyl ether-(CD 3) 3~d g [Fig. 33(a)] shows that the tertiary butyl group is not involved in this ion. The ion at m/e 67 is the fragmentation product of the ion at m/e 82 as discussed before [Section A-5 ( i i i ) ] . The removal of the degeneracy by labelling tends to confuse the region around m/e 71. However, the relatively larger abundance of the ion corresponding to m/e 71 in the undeuterated isomers shows up quite clearly. Another ion which has been found to arise by i n i t i a l g-cleavage of the ring and subsequent decomposition is the ion at m/e 58 (78). The mechanism of formation, which has been suggested i s as follows when applied to the present system: +. + m/e 170 m/e 58 If the mechanism above is operative the tertiary butyl group should have no effect and an ion should be present at m/e 58 in the undeuterated ethers. In the epimers deuterated at the a position the - 134 -ion should be at m/e 59. In the |? deuterated epimers the ion should appear at m/e 60 and with both positions labelled the ion should appear at m/e 61. From the experimental results obtained (Figs. 25, 27, 29, and 31) these ions are present in the order expected, however, the relative abundance is small and thus i t i s reasonable to conclude that this frag-mentation mode is a minor one compared to some of the others discussed. Finally, the ion at m/e 57 i s due to simple cleavage of the tertiary butyl bond and retention of the charge by this fragment. C-6. Conclusions Therefore,in general, the epimers of 4-t-butylcyclohexyl methyl ether do appear to fragment via pathways similar to those postulated for the corresponding alcohols. Trans 4-t-butylcyclohexyl methyl ether decomposes to lose methanol with a smaller probability as compared to trans 4-t-butylcyclohexanol. However, cis 4-t-butylcyclohexyl methyl ether gives rise to a relatively larger ion corresponding to loss of methanol perhaps due to steric effects. Another major difference observed in the spectra of the epimeric ethers is that of the relative abundance of the ions at m/e 114 and m/e 115. These ions predominate in the case of the cis isomer due to the possibility that abstraction from the tertiary butyl substituent can occur quite readily from one of the flexible forms of the ring. The observation that after the abstraction step the inter-mediate formed undergoes different reactions in cis 4-t-butylcyclohexyl methyl ether (leading to m/e 114 and m/e 115) and in cis 4-t-butylcyclo-hexanol (leading to m/e 99) may be a reflection of the effect of the group or atom bonded to the oxygen. - 135 -Fig. 25. Helium Light Source. Mass Spectra of (a) Trans 4-t-butylcyclohexyl methyl ether (b) Cis 4-t-butylcyclohexyl methyl ether. o z < o z m < 100 , • 50 80 H 1 . 40 60 . 1 H i- 30 40 . 10) • 20 20 • 10 0 1 l 0 100 80 60 40 20 0 60 120 m/e 120 m/e OCHj A T H lb) J . , .... ill , _JLH (-11 1 1 1 1 Fig. 26. Lyman a Light Source. Mass Spectra of (a) Trans 4-t-butylcyclohexyl methyl ether (b) Cis 4-t-butylcyclohexyl methyl ether. - 136 -Fig. 27. Helium Light Source. Mass Spectra of (a) Trans 4-t-butylcyclohexyl methyl ether-l-d (b) Cis 4-t-butylcyclohexyl methyl ether-l-d,. Fig. 28. Lyman a Light Source. Mass Spectra of (a) Trans 4-t-butylcyclohexyl methyl ether-l-d (b) Cis 4-t-butylcyclohexyl methyl ether-l-d . - 137 -g. 29. Helium Light Source. Mass Spectra of (a) Trans 4-t-butylcyclohexyl methyl ether-2,2,6,6-d (b) Cis 4-t-butylcyclohexyl methyl ether-2,2,6,6-d . • H T H ,l>„ (o) 1 1. . 1 100 120 m/e 60 eo 120 140 m/e 0 C H » 1 • H (b) | J—L, J 1 i ig. 30. Lyman a Light Source . Mass Spectra of (a) Trans 4-t-butylcyclohexyl methyl ether-2,2,6,6-d^ (b) Cis 4-t-butylcyclohexyl methyl ether-2,2,6,6-d,• 4 - 138 -100 -I 80 • 60 • 40 . UJ (J z 20 < o z 0 m < UJ 100 -I > < 80 -_J UJ or 60 • 40 -20 • 0 • ( C H 5 ' 5 C N . ^ ^ ^ 7 0 C M 3 DA JIUJIL, J j j j -80 100 120 m/e I I'll ..iH'll'l. U I 4 J . (CH3)3C Jbj. 0 C H 3 120 m/e 140 Fig. 31. Helium Light Source. Mass Spectra of (a) Trans 4-t-butylcyclohexyl methyl ether-1,2,2,6,6-d (b) Cis 4-t-butylcyclohexyl methyl ether-1,2,2,6,6-d 100 80 60 40 Ul o z 20 < a z o r> 00 < UJ 100 > 1-< 80 _J Ul or 60 40 20 0 0 1 T H (a) .III , , 1 1., 1. ,1 1 1 60 80 100 120 140 m/e 120 m/e 160 0 C H 3 1 ICH3I3C / / D I H IBL -.I , lliii . ,,ll 1 L 1, I|.I 1 | I L Fig. 32. Lyman a Light Source. Mass Spectra of (a) Trans 4-t-butylcyclohexyl methyl ether-1,2, 2,6,6-(b) Cis 4-t-butylcyclohexyl methyl ether-1,2,2,6,6-d,. - 139 -F i g . 33. Helium Light Source. Mass Spectrum of (a) Trans 4-t-butylcyclohexyl methyl ether-(CT) ) -d 100 -H ] eo-60- T H (0) «o 20- | 0 Ihll. .il .1,1 1 1 1,., 1 1. .1 40 20 W 10 60 80 100 120 140 160 180 m/e F i g . 34. Lyman a Light Source. Mass Spectrum of (a) Trans 4-t-butylcyclohexyl methyl ether-(CD,),-- 140 -40 60 80 100 120 140 160 180 m/e 33. Helium Light Source. Mass Spectrum of (b) Cis 4-t-butylcyclohexyl methyl ether-(CDo)_-i 34. Lyman a Light Source. Mass Spectrum of (b) Cis 4-t-butylcyclohexyl methyl ether-(CD-)o-d - 141 -Thus, from the differences observed in the spectra one may conclude that some of the major•fragmentation reactions taking place do appear to be influenced by the stereochemical arrangement of the atoms. D. The methylcyclohexanols The present section deals with the study of the epimers of 4, 3, i and 2-methyl substituted cyclohexanols and some of their deuterated i derivatives. The low resolution mass spectra of mixtures of the ) epimers using electron impact for ionization was done i n i t i a l l y by R.A. Friedel et a l . (68). Djeraesi et a l . (34) have also discussed these systems in some detail relating the abundant ions observed in the spectra to the position of the methyl substituent. 1. Cis and trans 4-methylcyclohexanols The spectra using photon impact for both cis and trans 4-methyl-cyclohexanols are shown in Fig. 35 (helium light source) and Fig. 36 (Lyman a light source). The differences observed in the spectra between the two isomers suggests that they do not isomerize to a common structure after ionization. The following discussion attempts to explain the decompositions leading to the [M-H20]+ ion in both isomers. Possible mechanisms for the formation of other common ions are also considered. Scheme 6 depicts the fragmentation routes involved in the decomposition of the alcohols. - 142 -Scheme 6 Cis and trans 4-methylcyclohexanols - 143 -D-l-1. The [M-H20]+ ion In general, one of the main differences observed using both light sources i s the relatively small abundance of the parent ion compared to the large peak corresponding to loss of water in the trans isomer [Fig. 35(a) and Fig. 36(a)]. In the cis isomer the parent peak is much more abundant but the [M-H20]+ ion is relatively smaller [Fig. 35(b) and Fig. 36(b)]. The values obtained for the [M-H20]+/M+ ratio for both cis and trans 4-methylcyclohexanols and their deuterated derivatives studied are shown in Table.IX. It thus appears that loss Table IX. [M-H20]+/M+ Ratio for Cis and Trans 4-Methylcyclohexanols and Their Deuterated Analogues (both light sources). [M-H20] /M [M-H20] /M trans 4-methylcyclohexanol 11.4 8.6 trans 4-methylcyclohexanol-1-d^ 15.0 11.5 trans 4-methylcyclohexanol-2,2,6,6-d4 16.1 12.0 trans 4-methylcyclohexanol-1,2,2,6,6-d,_ 18.2 11.6 cis 4-methylcyclohexanol 1.2 0.8 cis 4-methylcyclohexanol-l-d^ 1.2 0.9 cis 4-methylcyclohexanol-2,2,6,6-d^ 1.5 0.9 cis 4-methylcyclohexanol-1,2,2,6,6-d,. 1.4 0.9 Helium light source; Lyman a light source - 144 -of water i s a much more feasible process in the trans isomer. Again, this could be explained in terms of the availability of the cis hydrogen on C-4 in the trans isomer which i s not accessible in the i cis isomer, assuming the ring is s t i l l intact. Deuterium labelling results (Figs. 37, 38, 39, 40, 41, and 42) show that both the a and $ protons are retained in the majority of the ions at m/e 96 thus implying that the proton lost together with the hydroxyl group as water derives either from the C-4, C-3(C-5) positions of the ring or from the methyl substituent. The ion atm/e 96, m/e 99 and at m/e 100 in the spectra of cis 4-methylcyclohexanol-l-d^, 4-methylcyclohexanol-2,2,6,6-d^ and 4-methylcyclohexanol-l, 2,2,6 ,6-d,. respectively may represent some minor contribution from 1,2 elimination of water. However, these ions may also result from loss of water from the [M-l] + ion (this ion is present in the undeuterated alcohols, helium light source) or by loss of OH from the [M-2]+ ion. Contributions due to partially deuterated molecules, may, furthermore, also give rise to these ions. Therefore, a variety of different processes may be responsible for the appearance of these ions. In the trans isomer i t i s possible that both 1,3 and 1,4 elimination of water takes place, perhaps with the 1,4 loss being a more facile process due to the attainment of a favourable stereochemical arrange-ment. Deuterium labelling at position four would be able to resolve this question. The 1,3 mechanism may,as suggested by Green et a l . (2), be preceded by ring opening. Abstraction from the methyl group in the trans isomer appears to be unlikely i f one considers the ring intact (Fig. 65). - 145 -H OH Figure 65. Trans 4-methylcyclohexanol The hydroxyl radical cation site cannot approach close enough to the methyl group in any conformation for abstraction to occur readily. However, in the cis isomer, with the ring s t i l l intact, i t i s quite possible that abstraction from the methyl group can occur (Fig. Since the derivatives with a labelled methyl group were not available in the present work i t is not possible to make a conclusive statement regarding this fragmentation mode. Abstractions of this type from a substituent have also been observed in the case of cis and trans 1,4 cyclohexane diol (deuterated hydroxy groups) where i t was found that water loss in the cis isomer took place by elimination of T)^0 (12) . Similarly for cis 4-isopropylcyclohexanol loss of DOH was confirmed by specifically labelling the tertiary hydrogen on the isopropyl group (66). - 146 -A V H Figure 66. Cis 4-methylcyclohexanol Loss of water in the cis isomer can also take place by a 1,3 abstraction process. The relatively greater abundance of the [M-H^ P]^ " ion in cis 4-methylcyclohexanol as compared to cis 4-t-butylcyclohexanol may be attributed to the following factors. 1, More than one mechanism contributes to this ion, i.e. both loss by abstraction from the methyl substituent, and by a 1,3 elimination process. 2. The alternate fragmentation routes open to the ion in cis 4-t butylcyclohexanol after abstraction from the substituent are not possible in cis 4-methylcyclohexanol, i.e. the CH^: moiety would have to be eliminated (which is an unlikely process (34)) whereas in cis 4-t-butylcyclohexanol a stable molecule, C.HR, can be - 147 -eliminated. Therefore, perhaps i t is energetically more favourable to eliminate water instead. 3. The [M-H20]+ ion in cis 4-methylcyclohexanol may be more + stable relative to the [M-H^ O] ion in cis 4-t-butylcyclohexanol and therefore does not decompose readily leading to products of secondary reactions. i A l l or any one of the factors mentioned above may be contributing to the effect observed. The greater abundance in the cis isomer of the parent ion may be due to the fact that water loss by a 1,3 mechanism or by abstraction from the methyl group is a much slower process than the corresponding 1,4 elimination in the trans isomer and thus on the mass spectral time scale less of the cis molecular ions fragment. Metastable ions (Table X) corresponding to loss of water from the parent ion were observed i n ^all Table X. Observed m/e Value for the Ion m* Resulting from the Meta-stable Transition 114 -> 96 in Cis 4-Methylcyclohexanol and for the Corresponding Transition in the Deuterated Analogues j.a m* m." m l m2 cis 4-methylcyclohexanol 80.8 80.8 114 .96 cis 4-methyIcyclohexanol-l-d^ 81.8 81.8 115 97 cis 4-methylcyclohexanol-2,2,6,6-d^ 84.7 84.7 118 100 cis 4-methylcyclohexanol-1,2,2,6,6-d,. 85.7 85.7 119 101 Helium light source; Lyman a light source - 148 -the deuterated and non-deuterated cis isomers. No corresponding metastable ions were observed in the trans isomers. This may in turn imply that water loss in the trans isomer i s a much faster process and therefore most of the molecular ions decompose while in the ion chamber and thus are detected as normal fragment ions. D-l-2. The ion at m/e 81 The [M-rL^ O]"*" ion in both isomers subsequently decomposes by loss of a methyl radical to form the ion at m/e 81. This ion is found by + high resolution to be C,H„ . From the spectra of the deuterated b y derivatives (Figs. 37, 38, 39, 40, 41, and 42) one can conclude that the loss tf this radical does not simply take place by cleavage of the methyl substituent. Some ring opening mechanism is probably involved. The origin of the atoms comprising the methyl radical may come from any of the ring positions or the methyl substituent and on deuteration this degeneracy is removed thus leading to the presence of a group of ions around this mass number in the labelled molecules. Metastable ions have been observed corresponding to this transition in both deuterated and undeuterated cis and trans isomers (both light sources) and are shown in Table XI. This type of loss has also been observed in cyclohexanol as originating from the [M-R^ O]"*" ion (64). In this particular case the ring carbons are definitely involved. Similar observations have also been made in some a l i c y c l i c hydrocarbons where at f i r s t glance i t appears that the side chain is lost. It was found that the loss of a methyl group in some substituted cyclic compounds did not necessarily take place only by loss of the substituent, some contribution from the ring carbons was also evident (34). - 149 -Table X I . Observed m/e Value for the Ion m* Resulting from the Metastable Transition 96 -> 81 in both Cis and Trans 4-Methylcyclohexanols and for the Corresponding Transitions in the Deuterated Analogues m*a m* m l t&2 trans 4-methylcyclohexanol 68.3 68.3 96 81 trans 4-methylcyclohexanol-l-d^ 69.3 69.3 97 82 trans 4-methylcyclohexanol-2,2,6,6-d. 72.3 72.3 100 85 70.6 70.6 100 84 trans 4-methylcyclohexanol-l,2,2,6,6-d 73.2 73.2 101 86 5 71.5 71.5 101 85 cis 4-methylcyclohexanol 68.3 68.3 96 81 cis 4-methylcyclohexanol-1-d^ 69.3 69.3 97 82 cis 4-methylcyclohexanol-2,2,6,6-d. 72.3 72.3 100 85 70.6 70.6 100 84 cis 4-methylcyclohexanol-l,2,2,6,6-d 73.2 73.2 101 86 5 71.5 71.5 101 85 a b Helium light source; Lyman a light source D-l-3. The ions at m/e 57 and 58 The ions at m/e 57 and m/e 58 are of relatively • large abundance in the spectra obtained with the helium light source • (Fig. 35). These ions arise from molecular ions containing a greater amount of internal energy; the fragmentation sequence being one that requires more energy. In the spectra obtained with the Lyman a light source (Fig. , 36) (lower ionizing energy) these ions are not formed to any great extent. - 150 -The ion at m/e 57 is found to be a doublet comprising 25% of + + C.H. ions and the remaining 75%-C„H 0 ions (helium light source). H y D J A possible rationalization for the formation of the C.H_+ ion 49 is as follows; the charge in this case being retained by the hydrocarbon fragment. +• m H CH, -C,Hq0 CH3 3 5 CH, +C H CH / i i / m/e 57 m/e 114 If the mechanism is operative deuterium labelling results should indicate the presence of an ion at m/e 60 in both cis and trans 4-me thylcyclohexanol-2,2,6,6-d^ (Fig. 39) and the presence of an ion at m/e 57 in cis and trans 4-methylcyclohexanol-l-d^ (Fig. 37). The ion at m/e 60 in the other labelled substrate would be formed (Fig. 41). However, other mechanisms also give rise to ions at m/e 60 thus causing a degeneracy at this mass number. Experimentally this appears to be verified. The formation of the ion at m/e 57 (C^ H^ o"1") probably takes place by the mechanism suggested by Budzikiewicz et a l . (79) where 6 cleavage of the ring takes place. This fragmentation route is rational-ized as follows: - 151 -+ OH + + UH 3 lj|2 3 CH 2 ,m/e 114 m/e 57 The driving force of the reaction being the formation of the a l l y l i c ion at m/e 57. Deuterium labelling results from the present work confirms the incorporation of the a proton (Figs. 37 and 38) and one of the 6 protons (Figs. 39, 40, 41 and 42) which would lend further support to the mechanism mentioned, above. The ion at m/e 58 (Fig. 35) is also quite significant in the spectra of these alcohols. As this ion i s an odd electron ion i t is probably formed from the molecular ion by rearrangements and or multiple cleavage resulting in the loss of an even electron fragment. From the deuterium labelling results one observes that the a proton is retained in this ion (Figs. 37, 38, 41, and 42). Furthermore only one of the 3 protons is incorporated in the ion at m/e 58. Therefore, some mechanism for i t s formation would have to be postulated which would include retention of the hydrogens at C-l and one from C-2 (or C-6). A probable mechanism would possibly invoke 1-2 cleavage of the ring followed by hydrogen abstraction reactions and elimination of a neutral molecule, C^Hg. This elimination of a stable molecule may be the driving force for this fragmentation reaction. The methyl substituent cn cn cn ro n rt H CO of ,—v cr PJ o H H CO PJ 3 -> I cn 3 •C-ro i r t 3 a4 ro •< rt M D* o •< o o •<! O o 3* ro o 3* ro 3 X o PJ 3 • o 1—1 era ro M c 3 tr 1 H-TO D" rt CO o c H O ro RELATIVE ABUNDANCE 3 GO PJ 3 f 1 TO 3* CO o C H o ro R E L A T I V E ABUNDANCE 3 % 154 - zgi -100 UJ o z < Q Z Z> m UJ > 40 H 20 0 j ' OH T H ( O ) 1 , — J l Ii J 1 1, ,, U 1 .1 r - IOO UJ cr 80 H 60 UJ 40 o 20 00 < UJ > h-< UJ tr 100 80 60 40 20 C H 3 i H 60 <*3 60 OH ( O ) -A (b) 80 100 m/e 0H 80 m/e 100 - 50 - 40 • 30 • 20 • 10 . 0 120 • 25 h 20 - 15 • 10 1-5 120 m 55 U> Fig. 37. Helium Light Source Fig. 38. Lyman a Light Source Mass Spectra of (a) Trans 4-methylcyclohexanol-l-d^ (b) Cis 4-methylcyclohexanol-l-d^. 100 m/e m/e Fig. 39. Helium Light Source Fig. 40. Lyman a Light Source Mass Spectra of (a) Trans 4-methylcyclohexanol-2,2,6,6-d (b) Cis 4-methylcyclohexanol-2,2,6,6-d . 00 J> 1—' 3 • to CO a CO ro cn H-3 ro 3 o rt r 1 H H-£U 00 3" o rt Hi CO O Cu 3 — ' s«/ i-( n n H ro CO cu 3 4> w 3 4> ro 1 rt 3 3* ro ^ rt . h-1 3" o V! n O O n 3" i- 1 ro o X 3* cu ro 3 X O cu h-* 3 1 o M 1 ho M Tl V H-ro 00 • ># o> 1 ON RELATIVE ABUNDANCE a , ON • cu U l 1 cu 3 f 1 H-00 3* cn o 3 i-S n ro 3 . 3 % 141 R E L A T I V E ABUNDANCE o o 3 3 % 154 - SSI -- 156 -is most probably lost in the neutral fragment. Alcohols labelled with a deuterated methyl group would be able to confirm this suggestion. Labelling of the hydrogens at C-4, C-3 (C-5) would indicate which hydrogens are involved in the abstraction process and which of them are incorporated in the molecule formed. Cleavage of the ring probably takes place after ionization; this would remove a l l differences between the isomers and both cis and trans alcohols may fragment via the same pathway to lead to the ion at m/e 58. D-l-4. The ions at m/e 70 and m/e 71 The other two major ions in the spectra of cis and trans 4-methyl-cyclohexanols which have not been discussed yet are those at m/e 70 and m/e 71 (Fig. 35, helium light source), These ions are found by high resolution measurements to be hydrocarbon ions. They probably arise via a ring opening mechanism. Due to the removal of degeneracies by labelling (Figs. 37, 39, and 41) the mass region involved becomes quite complicated and d i f f i c u l t i e s arise in assigning which ions correspond to which original ion in the undeuterated alcohols. Therefore, the only statement possible at present is that after ring opening, depending on which bond is broken various hydrogen abstractions and eliminations can take place leading to the ions observed. 2. Cis and trans 3-methylcyclohexanols The spectra obtained for cis and trans 3-methylcyclohexanols (Figs. £3 and 44) using both light sources are almost identical. This would at f i r s t glance suggest that either the isomers lose their identity on - 157 -ionization or by coincidence give rise to identical spectra. An important point to consider is that the hydrogens on carbon four are equally available in both isomers in order to undergo the favourable 1,4 elimination of water, assuming the ring is intact,(Fig. 67). cis Figure 67. Trans and cis 3-methylcyclohexanols The only difference between the two boat conformations drawn (cis and trans isomers) is the position of the methyl substituent which would be axial in the trans isomer and equatorial in the cis isomer. This however, would most probably play some role in the s t a b i l i t y of the + [M-H^ O] ion formed. Scheme 7 shows the major fragmentation routes involved in the decomposition of these alcohols. - 158 -Scheme 7 + " C4 H9 C3H5O <r m/e 57 H OH 6 , m/e 114 " C3 H7 1,3 or 1,4 -H20 C^ H 7n12 m/e 96 -CH. + C 4H ?0 C6 H9 + m /e 71 m/e 81 Cis and trans 3-methylcyclohexanol - 159 -D-2-1. The ions at m/e 71, 57 and the [M-H 0]+ ion Deuterium labelling results for the epimers labelled at the a and g positions (Figs. 45, 46, 47, 48, 49, and 50) indicate that these protons are not involved in.the water molecule eliminated, thus implying that the hydrogens at C-4, C-5 (C-3) or on the methyl substituent are involved. Consider now the mechanism of formation of the ions at m/e 71 and m/e 57 which has been discussed in detail by Budzikiewicz et a l . (34). The ion at m/e 71 is found to be C^ H^ o"1" by high resolution measurements. Its mode of formation has been rationalized to occur as follows: H .OH OH OH CH- CH-CH. -C 3H 7 CH, + OH CH, /e 114 m/e 71 Deuterium labelling (present work) verifies the incorporation of the ct proton and one of the g protons (Figs. 45, 46, 47, 48, 49, and 50) The major portion of the ions at m/e 57 is found to be due to C^ H^ o"*" ions by high resolution measurements. Its formation has been postulated to take place as follows (79): H OH 1JJ2 OH CH 2 -uH, OH CH, -C 4H 9 CH, OH m/e 114 m/e 5 7 - 160 -This ion has been observed in electron impact spectra of a l l cyclic alcohols studied except for cyclobutanol (80). Deuterium labelling results from the present work verifies that the a proton is retained and trie of the 8 protons,(Figs. 45, 46, 47, 48, 49, and 50) thus supporting the mechanism postulated. Whether the ion at m/e 57 or the ion at m/e 71 is formed depends oh whether the 1,2 or the 1,6 bond cleaves after ionization. Since there is an equal probability of breaking either bond the larger abundance of the m/e 71 ion has to be ascribed to some other factors. It has been suggested that the stabilization of the ion at m/e 71 by hyperconjugatiop plays some role (34). Figure 51 shows the spectra obtained for cis and trans 3-methyl-cyclohexanol-4,4-(CD3)-d^ using the helium light source for ionization. In order to verify the positions of the label, the ions at m/e 71 and me/ 57 in the undeuterated alcohols were used. In Fig. 51 the majority of the ions corresponding to m/e 71 appear at m/e 74 indicating incorporation of three deuterium atoms. The ion at m/e 57 remains at m/e 57. The implication is that the three deuterium atoms are involved with the methyl group. The molecular ion appears at m/e 119, thus the two remaining deuteriums must be present at position four of the ring since this part of the molecule i s lost in the formation of both the ions and is therefore not detected. The assignment of the positions of labelling therefore agrees with the synthetic sequence used for their preparation. Some scrambling may have taken place during the synthesis,however, the majority of the ions seems to have retained the labels at the positions expected. 7ae same analysis - 161 -can be done on the spectra obtained with the Lyman a light source. Figure 52(a) shows the spectrum obtained using the Lyman q light source for trans 3-methylcyclohexanol -4,4-(CD 3)-d,.. The most abundant ion at m/e 101 corresponds to loss of H^ O from the molecular ion. A metastable ion at m/e 85.7 corresponding to this transition is also observed. This, therefore, suggests that loss of water in the trans isomer does not occur predominantly by a 1 , 4 mechanism. The major portion of the ion at m/e 100 corresponds to loss of DOH which would be due to 1 , 4 elimination. In order to reconcile with these results one xrould have to suggest that loss of water occurs mainly by a 1,3 mechanism in the trans isomer. The methyl substituent probably helps in l a b i l i z i n g this proton. The same observation can be made from the spectrum obtained with the helium light source [Fig. 51(a)]. The spectrum obtained for cis 3-methylcyclohexanol-4,4-(CD,j)-d,-[Fig. 52(b)] shox-js that the ion at m/e 100 is most abundant. This ion corresponds to loss of DOH from the molecular ion. However, an abundant ion is also present at m/e 99 which would be due to loss of D 2 O . A metastable ion at 82 .4 is also observed corresponding to the transition 119 -> 99. The loss of DOH can occur either by 1 , 4 elimination losing a deuterium atom from position four together with the hydroxyl group or by loss of a deuterium from the labelled methyl group (Fig. 68). Figure 68. Cis 3-methylcyclohexanol -4 ,4-(CD ) -d - 162 -Loss of B^O c a n occur i f the proton on the hydroxyl group gets exchanged with a deuterium atom from the labelled methyl group and then eliminates water by either of the two mechanisms discussed above. This type of hydrogen exchange between the hydroxyl hydrogen and the hydrogens at C-3 (C-5) which are in a 1,3 diaxial relationship has been observed in the study of cyclohexanol and i t s deuterated derivatives using electron impact by Ward and Williams (64). Shapiro et a l . (81) have also discussed hydrogen scrambling in the spectra (obtained with electron impact) of cyclohexanol and methylcyclohexanols. The majority of the ions at m/e 101 in the spectra of cis 3-methylcyclo-' , hexanol-4,4-(CD3)^-d^ is most probably due to loss of R^ O which would take place via a 1,3 mechanism. The ion at m/e 120 in both isomers would also contribute to the ions at m/e 102, m/e 101 and m/e 100 depending on whether R^ O, HDO, or D^ O is eliminated. It thus appears that the individual isomers eliminate water by more than one mechanism but to different extents. However, in the absence of labelling at the appropriate positions these effects may be degenerate and not so obvious. D-2-2. The ion at m/e 81 The. [M-H^ O]"1" ion in both isomers subsequently loses a methyl radical to form the ion at m/e 81. This, as in the case of 4-methyl-cyclohexanol, takes place either by loss of the substituent and/or ring opening with hydrogen abstraction reactions and eliminations leading to loss of part of the ring. The deuterium labelling results - 163 -confirm that randomization probably takes place and no s p e c i f i c atoms are l o s t (Figs. 45, 46, 47, 48, 49, 50, 51, and 52). Metastable ions have been observed for t h i s t r a n s i t i o n as indicated i n Table XII. Table XII. Observed m/e Value f o r the Ion m* Resulting from the Meta-stable T r a n s i t i o n 96 -* 81 i n both Cis and Trans 3-Methyl-cyclohexanol and f o r the Corresponding Transitions i n the Deuterated Derivatives m* m* i . m, trans 3-methylcyclohexanol 68.3 68. 3 96 81 trans 3-methylcyclohexanol-1-d 69.3 69. 3 97 82 I 67.6 67. 6 97 81 trans 3-methylcyclohexanol-2,2,6,6-d^ — 72. 3 100 85 trans 3-methylcyclohexanol-l,2,2,6,6-d^ 73.2 73. 2 101 86 trans 3-methylcyclohexanol-4,4-(CD,)^~d- 73.2 73. 2 101 86 71.5 71. 5 101 85 68.2 68. 2 101 83 c i s 3--methylcyclohexanol 68.3 68. 3 96 81 c i s 3--methylcyclohexanol-l-d^ 69.3 69. 3 97 82 J. 67.6 67. 6 97 81 c i s 3--mathylcyclohexanol-2,2,6,6-d. 72.3 72. 3 100 85 4 70.6 70. 6 100 84 c i s 3--methylcy.clohexanol-1,2,2,6,6-d,. 73.2 73. 2 101 86 c i s 3--methylcyclohexanol-4,4-(CD^) 3~d^ 72.3 73. 2 100 85 Helium l i g h t source Lyman a l i g h t source Fig. 43. Helium Light Source Fig. 44. Lyman a Light Source Mass Spectra of (a) Trans 3-methylcyclohexanol (b) Cis 3-methylcyclohexanol. S Co cn cn CO n fD n rt l-i CO o Hi '—s cr Co s * > o H i-i on Co 3 U> cn 3 LO fD 1 rt 3 pr (D rt 3* o ^ 1—1 o O 1-1 o O pr fD o X 3* m fD 3 X o CO t—1 3 i O t-1 h-1 i a . 1 t-1 I • RELATIVE ABUNDANCE * RO A CN ro o R O A o o o o o o o o o t* J— 1 . 1 1 1 * 1 1_ Ln o =. o ==-0Q R E L A T I V E ABUNDANCE % l 5 4 - S9T -3 PJ CO cn cn ro o t-i ' PJ o Mi cr PJ ^ * s , n H i-i CO P> 3 CO cn g U> ro 1 rt B a1 ro •<! rt h- 1 3 d n •<! h-1 O O O O 3" M ro o X 3* pj ro X o P3 h- 1 3 1 o ho (-» <* 1 ho NJ «* ON ho «* ON ON 1 p . ON 1 • 4> TO 33 ro M H -C 3 tr< H -00 3* CO o 3 i-i O ro RELATIVE ABUNDANCE 3 % 141 era 00 PJ 3 r 1 TO 3-CO o c H n ro R E L A T I V E ABUNDANCE 3 % 154 - 991 -H-00 •i> sO PC s ro fu M cn H-cn 3 3 co "3 tr1 ro H-o •00 rt pr >~t rt Cu CO O O Ml 3 H '—s O cr (U ro — ^ n H i-( cn Cu LO cn 3 LO ro 1 rr 3 pr ro V! rt I—1 cr o M" o o i—1 *<! O n =r ro O X pr ft) ro 3 X. o cu M 3 1 o t—1 M i 00 ro i—* • ro Ul <* O ro • RELATIVE ABUNDANCE ON ON I -CU ON Ul I • CU Ul Cu 3 0Q pr CO o 3 ri n ro 3 % 141 R E L A T I V E ABUNDANCE 3 o o o 91 O % 154 - £91 -00 Ul M cd ro 0J h-1 CO M-CO 3 3 CO X) r-1 ro H-o OP rt cr H rt Co CO o o Ml c n —s o cr ro ^ — ' n H I-i w CO 3 GO CO t 3 GO ro 1 rt 3 cr ro rt cr O '•<! D n I—1 •<! O o cr M ro O X cr p> ro 3 X o Co 3 i O •n -o h-1 p-* | 00 • ** Ul o Is) o • RELATIVE ABUNDANCE GO O w o I GO Cu ^—' Ul I . CX Ul CO 3 p H-00 cr CO o c n o ro 3 % 141 R E L A T I V E ABUNDANCE o o 3 3 CO % 154 - 891 - 169 -3. Cis and trans 2-methylcyclohexanols The spectra obtained for both cis and trans 2-methylcyclohexanol using the Lyman a light source for ionization are shown in Fig. 54. In general they differ only in the abundance of the parent ion and the [M-R^ O]"1" ion. The spectra obtained using the helium light source (Fig. 53) show even less of a difference, the intensity of the [M-H^ O]"*" ion being slightly greater in the cis isomer. The possible major decomposition pathways involved in these alcohols are shown in Scheme 8. Once again, perhaps one of the major reasons for this similarity is the availability of the hydrogens on carbon four which would make elimination by water by a 1,4 process equally probable in both isomers. D-3-1. The [M-H20]+ ion + + The values obtained for the [M-R^ O] /M ratio for both the deuterated and undeuterated alcohols are shown in Table XIII. Table XIII. [M-H20]+/M+ Ratio for Cis and Trans 2-Methylcyclohexanols and Deuterated Analogues [M-H20]+/M+a [M-H20]+/M+b trans 2-methylcyclohexanol 2.6 1.6: trans 2-methylcyclohexanol-l-d^ 2.2 1.6 trans 2-methylcyclohexanol-2,6,6-d3 2»8 1.6 trans 2-methylcyclohexanol-l,2,6,6-d. 2.6 1.7 - 170 -Scheme 8 C 3H 50 + ~ C4 H9 m/e 57 -C 2H 4 C4H?0 C 5 H 8 + C7 H12' m/e 96 -CH, + C 6H g m/e 71 m /e 68 m/e 81 Cis and trans 2-methylcyclohexanol - 171 -Table XIII. (Continued) cis 2-methylcyclohexanol cis 2-methylcyclohexanol-1-d^ cis 2-methylcyclohexanol-2,6,6-d^ cis 2-methylcyclohexanol-l,2,6,6-d a b Helium light source; Lyman a light source The difference in the values of the ratio between the two isomers may be due to the fact that less of the molecular ions decompose in the trans isomer as indicated by the larger, parent ion especially i n the spectrum obtained with the Lyman a light source [Fig. 54(a)]. No obvious reason for this observation can be found. Assuming the ring is s t i l l intact both 1,4 and 1,3 mechanisms may be operative i n both isomers. Deuterium labelling results suggest that no significant 1,2 elimination of water occurs in either of the isomers (Figs. 57, 58, 59, and 60). Metastable ions corresponding to loss of water are observed in the spectra of both isomers and their deuterated derivatives as shown in Table XIV. It i s possible that the methyl group in both isomers is at a position where i t does not have much influence on the elimination reaction and therefore w i l l not affect the decomposition pathways taken by the 'individual isomers. These routes may be different or the same for both isomers. Only labelling at the remote positions of the [M-H20]+/M+a 3.4 3.6 4.0 3.3 [M-H20]+/M+b 3.4 3.2 3.3 4.0 - 172 -Table XIV. Observed m/e Value for the Ion m* Resulting from the Metastable Transition 114 96 in Both Cis and Trans 2-Methylcyclohexanol and for the Corresponding Transitions in the Deuterated Analogues. m* m* m l ^2 trans 2-methylcyclohexanol 80.8 80.8 114 96 trans 2-methylcyclohexanol-1-d^ 81.8 81.8 115 97 trans 2-methylcyclohexanol—2,6J6-d3 83.8 83.8 117 99 trans 2-methylcyclohexanol-l,2,6,6-d^ 84.7 84.7 118 100 cis 2--methylcyclohexanol 80.8 80.8 114 96 cis 2--methylcyclohexanol-l-d^ 81.8 81.8 115 97 cis 2-- methyIcyclohexanol-2,6,6-d^ 83.8 83.8 117 99 cis 2--methylcyclohexanol-1,2,6,6-d^ 84.7 84.7 118 100 Helium light source; Lyman a light source ring may be able to resolve this question. A similar experimental observation has been made by Doljes and Hanus (19) who found that the mass spectra of cis and trans 2-t-butylcyclohexanol (electron impact) are almost identical whereas the epimers with the tertiary butyl group at either the three or four position gave markedly different spectra. - 173 -D-3-2. The ion at m/e 81 The [M-H^ O]"*" ion in both isomers as in the case of 4-methylcyclo-hexanol and 3-methylcyclohexanol loses a methyl radical to form the ion at m/e 81. This again appears to be a non-specific process. D-3-3. The ions at m/e 57 and m/e 71 The ion at m/e 57 is almost exclusively due to the C^ H^ o"'" fragment, the formation of which has been discussed before in connection with the other methylcyclohexanols. Similarly for the ion at m/e 71 which is ' due to the C^ H^ O* ion. The fragmentation route is the same as outlined under 3-methylcyclohexanol, this time with the methyl group substituted at the two position. In the spectra of both cis and trans 2-methylcyclo-hexanol (helium light source, Fig. 53) one observes that the ion at m/e 57 is of greater abundance relative to the ion at m/e 71. This observation has been attributed to the fact that a more highly substituted bond is prone to rupture more easily (34). The i n i t i a l breaking of the ; 1,2-bond leads to the ion at m/e 5 7 in this case. D-3-4. The ion'at m/e 68 Another abundant ion in the spectra of both isomers (helium light source, Fig. 53) is the ion at m/e 68. This ion is most probably formed by loss of C^H^ from the [M-H^ O]"*" ion. Two possible major routes are as follows depending on whether the [M-H^ O]"*" ion is formed via a 1,3 or 1,4 mechanism. - 174 -1) (1,4 loss) 3 1 7 CH 3 -C 2H 4 H 7 XH-m /e 114 /e 96 m /e 68 H OH i/e 114 :H, -H20 (1,3 loss) m/e 96 CH„ H' H CH, "C 2H 4 .CH 2 ^CH. i/e 68 The driving force for the reaction i s probably the formation of a stable C2H^ molecule. Path 1 should lead to an ion at m/e 69 in the a deuterated molecules (Figs. 55 and 56) and at m/e 69 in the g deuterated molecules (Figs. 57 and 58). Route 2 should lead to an ion at m/e 68 in the a deuterated isomers (Figs. 55 and 56) and at m/e 69 in the g deuterated isomers (Figs. 57 and 58). In the epimers Fig. 53. Helium Light Source Fig. 54. Lyman a Light Source Mass Spectra of (a) Trans 2-methylcyclohexanol (b) Cis 2-methylcyclohexanol. 100 m/e m/e Fig. 55. Helium Light Source Fig. 56. Lyman a Light Source Mass Spectra of (a) Trans 2-methylcyclohexanol-l-d^ (b) Cis 2-methylcyclohexanol-l-d^. Fig. 57. Helium Light Source Fig. 58. Lyman a Light Source Mass Spectra of (a) Trans 2-methylcyclohexanol-2,6,6-d"3 (b) Cis 2-methylcyclohexanol-2,6,6-d3. S Co cn cn CO ro o rt H CD of /—s cr Co N—s n H i-i cn PJ 3 cn g ro 1 rt g cr ro rt t—1 cr o n o i—1 v< o o cr h-1 ro o cr ro 3 o CU M 3 1 o M 1 t-1 ON <•» ON ON 1 <* a . ON 1 • Cu 00 RELATIVE ABUNDANCE 3 % 141 R E L A T I V E ABUNDANCE % 154 - 8LT ~ - 179 -labelled at both the a and g positions, path 1 should give rise to an ion at m/e 70 whereas route 2 would give rise to an ion at m/e 69 (Figs. 59 and 60). From the experimental results i t appears that both mechanisms may be operative. D-4. Conclusions Therefore, in general, from the experimental results and from the foregoing discussion i t appears that the epimers of 4-methylcyclo-hexanol do not isomerize to a common structure before fragmenting. The epimers of 3-methylcyclohexanol appear to lose water by the same routes but to differing extents. Deuteration at the remote positions of the ring removes degeneracies present in the undeuterated isomers and thus allows some of the differences to be observed. The epimers of 2-methylcyclohexanol give rise to mass spectra which are very similar. However, there may be some stereospecific fragmentation reactions taking place, which are not obvious in the absence of labelling at the appropriate positions. In fragmentation reactions where ring opening takes place some similarities are observed. There are even amongst these some reactions which are more prominant in one of the methyl series compared to the others. The spectra obtained with the Lyman a light source are simple and limited mainly to the primary fragmentation sequence products. Those obtained with the helium light source tend to show a greater number of ions formed by secondary fragmentation modes and by ring opening processes which presumably require more energy which is available in this case. - 180 -E. General observations A comparison of the spectra of the non-deuterated isomers to that of the deuterated isomers (both light sources) in a l l the systems studied show that some fluctuation in the relative abundances of the corresponding ion exists. This difference may be due to the operation of an isotope effect. Analogous effects are known to exist in solutions from the study of the kinetics of some reactions (82). Stevenson (83) has pointed out that no difference in ionization efficiency is to be expected between light and heavy molecules. However, i t has been pointed out that substitution with a heavier isotope does bring about a decrease in the amount of fragmentation that occurs (84). These observations were made when electron impact was used for ionisation. From the present work i t appears that some ions increase slightly in abundance whereas others decrease. No definite trend seems to be involved except for the cases where a deuterated tertiary butyl group is present in the molecule. In these instances the relative abundance of the ion corresponding to the tertiary butyl cation does decrease. It is possible that some of these differences observed may be due to slight changes in the operating conditions of the light source which may in turn effect the relative contributions from competing processes. Furthermore, since the sensitivity of mass spectra obtained with photons is much lower some small error in the physical measurement of the peak heights may be introduced. Some or a l l of these factors may be additive and lead to the differences observed. Whether label scrambling is a significant process in the mass spectra obtained is d i f f i c u l t to assess. Except for the case of cis - 181 -3-methylcyclohexanol-4,4-(CD3)-d,_ (Figs. 51 and 52) and perhaps for cis 4-t-butylcyclohexanol-(CD^)^-dg (Figs. 13 and 14) where label scrambling was invoked to rationalize the formation of some ions, no other direct evidence was obtained for such processes. - 182 -CONCLUSIONS From the foregoing discussion a few general conclusions can be arrived at. It appears that the molecular ions studied do not necessarily fragment from their lowest energy conformations and that the energy imparted to the molecular ions on ionization determines the rate of the various processes. The spatial arrangement of the atoms or groups in a molecule also has an important effect on the mode of fragmentation especially when large substituents are present. The results obtained for cis 4-t-butylcyclohexanol and for cis 4-t-butylcyclohexyl methyl ether show the effect of the large tertiary butyl ^roup quite clearly in the fragmentation pattern observed. It is proposed that the tertiary butyl substituent participates in the formation of the ions at m/e 99 in cis 4-t-butylcyclohexanol and at m/e 114 and m/e 115 in cis 4-t-butylcyclohexyl methyl ether. The functional group also plays an important role in the breakdown pathways involved. The similar fragmentation modes which both cis and trans 4-t-butylcyclohexyl acetates undergo indicates that in this case, even though the rest of the molecule is the same as that in the alcohols and the ethers, the acetate group lays a leading role. This group being larger and also due to the presence of the carbonyl oxygen, - 183 -fragmentation routes are now accessible which were not possible in the case of the alcohols and ethers (4-t-butyl system). The completely different fragmentation routes that the proposed ion (i.e., after abstraction from the tertiary butyl group) undergoes in both cis 4-t-butylcyclohexanol and cis 4-t-butylcyclohexyl methyl ether may again reflect the role of the functional group. Perhaps the fact that the methoxy group is more electron donating relative to the hydroxy group is responsible in part for the operation of a different fragmentation route. A smaller group, for example methyl in 4-methylcyclohexanol does not play as important a role since the side reactions which are available to the tertiary butyl group are not possible in this case and therefore less differences are observed in the spectra of the individual isomers. The position of substitution also plays an important role depending on the fragmentation route involved. The loss of water in trans 4-t-butylcyclohexanol and the loss of methanol in trans 4-t-butylcyclohexyl methyl ether appears to be a highly stereospecific reaction. In the 3-methylcyclohexanols both 1,3 and 1,4 mechanisms appear to be operative in the loss of water, however, to different extents in the respective isomers. Regarding the other alcohols studied no definite statement can presently be made about the mode of loss of water. Further studies possibly with other deuterated analogues may be able to resolve these questions. The fact that 1,2 elimination does not appear to be a favourable mode of elimination in the alcohols studied, further suggests that the attainment of a five membered or greater transition state is energetically more feasible. In the case of the 4-t-butylcyclohexyl - 184 -acetates, due to the large acetate group, a favourable transition state i s now possible with the hydrogens at carbon two or six, thus leading to 1,2 elimination. The use of lower ionizing energies is also of use in uncovering rearrangement processes. An increase in the relative abundance of these ions would indicate that these fragmentation reactions have lower frequency factors and activation energies. The ion at m/e 99 in cis 4-t-butylcyclohexanol at f i r s t glance appears to be due to a single bond cleavage (i.e., the bond between the tertiary butyl substituent and the ring). However, labelling results suggest that this ion is formed by a rearrangement process. The relative abundance of this ion increases markedly in the spectrum obtained with the Lyman a radiation compared to that obtained with the helium light source. Thus i t may be possible to identify ions which arise due to rearrangement reactions without the aid of labelling. Double rearrangement reactions as represented by the ion at m/e 115 in cis 4-t-butylcyclohexyl methyl ether also appear to have low activation energies. The relative abundance of this ion also increases in the spectrum obtained with the lower ionizing energy. Since label scrambling processes are generally rearrangement reactions, contributions from these would increase in spectra obtained with low ionizing energies. In the present work two ions which appear to arise via some scrambling reaction are the ions at m/e 101 and m/e 99 in cis 4-t-butylcyclohexanol-(CD^)^-d^ and cis 3-methylcyclohexanol-4,4-(CD^)-d,. respectively. The relative abundance of these ions also increases in the spectra obtained with the Lyman a light source compared - 185 -to those obtained with the helium light source thus lending further support to the statement made above. Photoionization mass spectrometry may be useful especially in cases where thermal decomposition reactions can lead to complications and erroneous conclusions. The spectra obtained with the Lyman a light source are limited to ions which are products of primary fragmentation sequences and would be of use in cases where small parent and primary reaction product ions are observed using conventional methods of mass spectrometry especially i f these are of diagnostic value. In the spectra obtained with the helium light source more ions are observed and the spectra are qualitatively similar to those obtained with electron impact. However, again a larger abundance of high mass ions is observed and these may be of some use in the interpretation of the spectra. 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