THE CRYSTAL AND MOLECULAR STRUCTURES OF SOME ORGANIC COMPOUNDS by THOMAS CHUNG-WAI MAK Sc.(Hon.); University of B r i t i s h Columbia, i960 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENT FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in the Department of CHEMISTRY We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA . September, 1963 In presenting t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e for reference and study. I f u r t h e r agree that per-mission for extensive copying of t h i s t h e s i s for s c h o l a r l y purposes may be granted by the Head of my Department or by h i s representatives. I t i s understood that copying, or p u b l i -c a t i o n of t h i s t h e s i s f o r f i n a n c i a l gain s h a l l not be allowed without my w r i t t e n permission. Department of The U n i v e r s i t y of B r i t i s h Columbia, Vancouver 8 , Canada. PUBLICATIONS A.R. Osborn, T.C.W.Mak and E. Whalley; Pressure Effect and Mechanism i n Acid Catalysis. V I I I . Hydrolysis of Acetamide and Benzamide. Can. J. Chem. , 39, 1,1.01 (1961). T.C.W. Mak and J. Trotter: The Structure of B i ~ phenylene. P r o c Chem. Soc,, 163 (1.961). T.C.W. Mak and J. Trotter; The Crystal and Molecular Structure of Biphenylene. J. Chem. S o c , 1(1962). T.C.W. Mak and J. Trotter: The Crystal and Molecular Structure of ". Methoxycarbonylmercuric Chloride. J. Chem. S o c , 3243 (1.962). T.C.W. Mak and J. Trotter; The Crystal Structure of £-Chloronitrobenzene. Acta Cryst., _15, 1078 (1962). T.C.W. Mak and J. Trotter: Crystallographic Data for Some Acenaphthene Derivatives. Acta Cryst., 16, 324 (1963). CHtS/^tS-r^t ~tf^G/*fe-line . University of B r i t i s h Columbia FACULTY OF GRADUATE STUDIES PROGRAMME OF THE FINAL ORAL EXAMINATION FOR THE DEGREE OF DOCTOR OF PHILOSOPHY of THOMAS CHUNG=WAI MAK B.Sc.(Hon.), The University of B r i t i s h Columbia THURSDAY, JULY 18, 196.3, at 9;30 A.M. IN ROOM 261, CHEMISTRY BUILDING COMMITTEE IN CHARGE Chairman:^ F.H. Soward W.A. Bryce W. Opechowski H.C. Clark S.A. Sutherland J.P. Kutney RiMi Thompson J. Trotter External. Examiner; E.C. Lingafelter University o f Washington THE CRYSTAL AND MOLECULAR STRUCTURES OF SOME ORGANIC COMPOUNDS ABSTRACT . The c r y s t a l and molecular structure of biphenylene has been refined from normal and generalized projections along the c-axis. The gross features of the structure previously determined have been confirmed. A comparison of the measured bond lengths and those calculated by simple resonance theory and by molecular o r b i t a l theory indicates that the l a t t e r gives a better description of the electron d i s t r i b u t i o n i n the molecule. In terms of the Kekule structures the preferred formulation i s that which describes the molecule as a cyqlobutane derivative. These conclusions are i n agreement with the chemical behaviour of biphenylene and i t s derivatives. An adduct formed by passing carbon monoxide into a solution of mercuric chloride i n methanol has been shown by X-ray analysis to be methoxycarbonylmercuric" .< chloride. The coordination around the mercury atom i s exactly l i n e a r , and the molecule i s planar, except for the methyl group, whose carbon atom i s displaced by 0.39A from the plane of the other atoms. A re-examination of the c r y s t a l structure of p_-chloro-nitrobenzene has established that the space group i s not Pa as previously assigned, but*P2^/a which implies a molecular centre of symmetry. Projections along the a-and b-axes indicate that this i s achieved by a disordered arrangement of molecules involving random interchange of the positions of the chlorine atom and n i t r o group. A series of acenaphthene derivatives has been examined by X-rays, and the c r y s t a l and molecular structures of acenaphthenequinone, cis-1,2-acenaphthenediol and c i s - 1 , 2-acenaphthenediol d l n i t r a t e determined with precision. In a l l three compounds the carbon skeleton i s planar, and the s t r a i n i n the p e r i - r i n g i s almost e n t i r e l y taken up by valency-angle- d i s t o r t i o n s , both i n the p e r i - r i n g and in the naphthalene rings. The vari a t i o n of bond lengths i n the aromatic nucleus i s similar to that i n naphthalene. The acenaphthenequinone molecule i s planar, and the short peri-bonds (average value 1.48i0.OI4A) are i n d i -cative of conjugation between the aromatic rings and the carbonyl groups. The C^ =C2 bond distance of 1.53*-0.02A agrees we l l with the value reported for acenaph-thene„ In cis-1,2-acenaphthenediol the peri-bonds are s i g n i -f i c a n t l y shortened (mean length 1.48-OToio-A) while the 1.60i0,0l4A C^-C2 bond distance shows the effect of ring s t r a i n and s t e r i c repulsion of the non-bonded oxygen atoms. The c r y s t a l structure consists of zigzag chains of intermolecular hydrogen bonds formed between mole-cules related by a screw axis, the intermolecular 0.... 0 distances being 2.72 and 2.70A. The C]_-C2 bond in cis-1,2-acenaphthenediol d i n i t r a t e has a length almost i d e n t i c a l to that i n the d i o l . There i s no bonding between the nitroxy groups, which are planar and inc l i n e d at angles of +62.1° and +71.2° to the plane of carbon atoms. GRADUATE STUDIES F i e l d of Study: . Chemistry Crystal Structures Topics in Physical Chemistry Topics in Inorganic Chemistry Topics in Organic Chemistry Spectroscopy and Molecular Structure Quantum Chemistry S t a t i s t i c a l Mechanics Theoretical Chemistry K.B. Harvey J. Trotter J.A.R. Coope R.F. Snider Staff Staff Staff J.A.R. Coope R.F. Snider R.F. Snider Related Studies: C l a s s i c a l Mechanics Quantum Mechanics Abstract Algebra Computer Programming W..Opechowski W. Opechowski N.Ji Divinsky Miss Charlotte Froese - 11 -ABSTRACT The c r y s t a l and molecular structure of biphenylene has "been refined from normal and generalized projections along the c-axis. The gross features of the structure previously determined have "been.confirmed. • A comparison ,of the'measured,bond, lengths ,and those calculated by simple resonance theory and by molecular o r b i t a l theory indicates that the l a t t e r gives a better description .of the electron d i s t r i b u t i o n i n the molecule. In terms of the Kekule structures the preferred formulation i s that which describes the molecule as a cyclobutane derivative. These conclusions are i n agreement with the chemicalibehaviour of biphenylene and i t s derivatives. An adduct formed by passing carbon monoxide into a solution of mercuric chloride i n methanol has been shown by X-ray analysis to be methoxycarbonyl-mercuric chloride. The coordination around the mercury atom i s exactly"linear, and the molecule i s planar, except for the methyl group, whose carbon atom i s o displaced by 0 .39 A from the plane of the other atoms. A re-examination of the c r y s t a l structure of p-chloronitrobenzene has established that the space group, i s not Pa as previously assigned, but ^^./a which implies a molecular centre of symmetry. Projections along the a- and b-axes indicate that t h i s i s achieved by a disordered arrangement of molecules involving random interchange of the positions of the chlorine atom and n i t r o group. A series of acenaphthene derivatives has been examined by. X-rays, and the c r y s t a l and molecular structures of acenaphthenequinone, c_is_»l,2-acenaphthenediol and cis-l , 2-acenaphthenediol d i n i t r a t e determined with precision. In a l l three compounds the carbon skeleton,is planar, and the s t r a i n i n the p e r i - r i n g i s almost e n t i r e l y taken up by valency-angle d i s t o r t i o n s , both i n the p e r i - r i n g and i n the naphthalene rings. The va r i a t i o n of bond lengths i n the aromatic - i i i nucleus i s similar to that i n naphthalene. The acenaphthenequinone molecule i s planar, and the short peri-bonds (average value l.kQ + 0.01^%) are indicative of conjugation between the aromatic rings and the carbonyl groups. The C-^-^ bond distance of o 1.53+0-02A agrees we l l with the value reported f o r acenaphthene. In c i s -1,2 -acenaphthenediol the peri-bonds are s i g n i f i c a n t l y shortened (mean length 1.1+8+0.01QA) .while the 1.60+0.Ol^A bond distance shows the effect of r i n g s t r a i n and s t e r i c repulsion of the non-bonded oxygen,atoms. The c r y s t a l structure consists of zigzag chains of intermolecular hydrogen bonds formed between molecules related by a screw axis, the intermolecular 0 0 distances being 2-72 and 2-70 A. The C-^ -C^ "bond i n c _ i s - l , 2-acenaphenediol d i n i t r a t e has a length almost i d e n t i c a l to that i n the d i o l . There i s no'bonding between the nitroxy groups, which are planar and i n c l i n e d at angles of +62.1° and +71-2° to the plane of carbon atoms. - V -ACKNOWLEDGEMENTS I gratefully, acknowledge the in s p i r a t i o n and.guidance of Dr. James Trotter throughout my graduate study. His u n f a i l i n g encouragement and warm personality have made my. association with him a most memorable one. My thanks.are due to Professor J.M. Robertson for the sample of biphenylene, to Dr. J. Halpern and Mr. A.L-W. Kemp for the,crystal sample of methoxycarbonylmercuric chloride,,to Dr. M.P. Cava for crystals of several derivatives of benzocyclobutene, and to Drs. L.D. Hayward and I.G. • Csizmadia for, the series of acenaphthene derivatives. I am especially grateful to Dr. Hayward for his continuing interest i n the problem, for much helpful discussion and advice,,and for bringing to my.attention important new data i n advance of publication. I am also indebted to Dr. F.R. Ahmed for kindly making available his IBM 1620 Fourier and structure factor programs,.to Mr. N. Camerman for various a u x i \ l i a r y programs,, and to the s t a f f of the UBC Computing Centre for assistance with the operation of the computer. For some of the i l l u s t r a t i o n s i n t h i s thesis I wish to thank Mr. W. Griba. F i n a l l y I wish to record my.appreciation to the National Research Council of Canada for the award of a bursary for the period I96O-61,. and a studentship for the period I 9 6 I - 6 3 . To MY PARENTS for t h e i r affection, s a c r i f i c e and encouragement - v i -TABLE OF CONTENTS Page TITLE PAGE ( i ) ABSTRACT ( i i ) ACKNOWLEDGMENTS ' (v) TABLE OF CONTENTS . . . . . . ( v i ) LIST OF FIGURES . . ( v i i i ) LIST OF TABLES (x) GENERAL INTRODUCTION 1 PART I. THEORY AND PRACTICE OF CRYSTAL-STRUCTURE ANALYSIS 3 I. Elementary Crystallography k A. Crystal Geometry k B. Symmetry of Crystals and Point Groups k C. Space Lattices 7 D. Space Groups 7 I I . D i f f r a c t i o n of X-Rays by Crystals 9 A. . Scattering ef X-Rays by Crystals 9 B. Conditions for X-Ray D i f f r a c t i o n Maxima 9 ' C The Reciprocal Lattice 11 D. The Structure Factor 12 E. The Intensities of- X-Ray Reflexions 13 F. Representation of the Crystal as, a Fourier Series . . . . 15 G. The Phase Problem ' 16 I I I . The Determination of Crystal Structures 17 A. Two-Dimensional Projections 17 B. The Interpretation of D i f f r a c t i o n Patterns 17 C. Methods for Obtaining an Approximate Structure 17 D. Refinement Procedures 19 E. Assessment of Accuracy . . . 22 PART I I . THE CRYSTAL AND MOLECULAR STRUCTURES OF BIPHENYLENE, .METHOXYCARBONYLMERCURIC CHLORIDE AND p-CHLORONITROBENZENE . . 2k I. Biphenylene 25 •A. Introduction 25 •B. Experimental • 29 C. Structure Analysis 30 D. Discussion 1+0 - V l l -Page I I . Methoxycarbonylmercuric Chloride ^3 A. Introduction U3 B. Experimental kk C. Structure Analysis U5 D. Discussion 51 ' I I I . p_-Chloronitrobenzene 52 A. Introduction 52 B; Experimental 52 C. Structure Analysis 53 D. Discussion 58 PART' I I I . X-RAY STUDIES ON SOME DERIVATIVES OF ACENAPHTHENE . . . . 60 I. Acenaphthene and Derivatives 61 A. Introduction 6 l B. • The Structure of Acenaphthene 62 C. Survey of Known" Analyses of Acenaphthene Derivatives . 63 I I . Acenaphthenequinone 66 A. Introduction 66 B. Experimental 66 C. Structure Analysis 68 D. Discussion 77 I I I . cis-1,2-Acenaphthenediol 80 A. Introduction 80 B. Experimental 82 C. Structure Analysis 83 D. Discussion 91 IV. c i s-1,2-Acenaphthenediol Dinitrate 95 1 A. Introduction 95 B. Experimental 96 C Structure Analysis 97 D. Discussion 106 V. General Conclusions 112 APPENDIX I. STRUCTURE FACTOR TABLES Ilk APPENDIX I I . CRYSTALLOGRAPHIC DATA FOR SEVERAL ORGANIC COMPOUNDS. . 13O REFERENCES 135 - v i i i -LIST OF FIGURES Page 1. The Ik Bravais l a t t i c e s 6 2. Scattering from a row of atoms i n a l a t t i c e d irection 10 3- Modulus and d i r e c t i o n of the d i f f r a c t i o n ,vector S 10 1+. Relationship .between S and,the plane (h-jj^h^) 10 5- D i f f r a c t i o n i n reciprocal space 13 6. Effect of a small error i n atom location on D 20 1 /Biphenylene 7. Electron-density projection along [oOl] • . • 32 8. Measured bond distances and valency angles 35 9- Mean bond distances and valency angles '. 36 10. Projection of the structure -along [00l] 38 Methoxycarbonylmercuric Chloride 11. Patterson projections along [00l] and[l06] 1+6 12. Electron-density projection along [00l] 1+8 13- Electron-density projection along [ l00] '. . . 1+9 lk. Dimensions of the molecule ' 50 15. Projection of the structure along [001~J 50 p-Chloronitrobenzene 16. Patterson projections along [lOO*] and . [oio] 5)4 17- Electron-density projection along [lOO] 56 l 8 . Electron-density projection along [Old] 57 19- Mean-bond lengths and valency angles i n naphthalene -and i n some compounds containing the acenaphthene nucleus 61+ Ac enaphthenequinone 20. Relation,of the o r i g i n of space group P 2 1 2 1 2 1 to the origins , of i t s p r i n c i p a l projections 67 - i x -Page 21. Patterson projection along [ o o i ] ' . 69 22. Electron-density projection along [ o o i ] ' 71 23. Electron-density projection along [ l O o ] 72 24. Numbering and average dimensions of the molecule 76 25- Projection of the structure along [OOI] 1 78 cis-1 ,2-Acenaphthenediol 26. Patterson projection along J010J 84 27- Electron-density projection along [ o i o ' | 86 28. Numbering and average dimensions of the molecule 90 29- Projection of the structure along [010J 92 30. Perspective diagram showing the hydrogen bonding 93 cis-1 ,2-Acenaphthenediol Dinitrate 31. Patterson projection along [0l6] ' 98 32. Electron-density projection along [010] 100 33- Numbering and average dimensions of the cis -1 ,2-acenaphthenediol portion of the molecule 104 34. Projection of the structure along [oiO^J 1 107 35* Perspective diagram of the molecular structure • • • 108 36. CENCO Petersen molecular model 109 37- Dimensions of the nitroxy group 110 38. Average dimensions of the naphthalene moiety of the acenaphthene system 113 - X " LIST OF TABLES Page •I.' Symmetry Elements of Crystals 5 I I . The 32 Point Groups or Crystal Symmetry Classes 5 Biphenylene I I I . P o s i t i o n a l Parameters •• . . . 3I4. IV. Orientation of Molecules i n the Unit C e l l 37 V. Measured and Calculated Bond Lengths 1+0 Methoxycarbonylmercuric Chloride VI. P o s i t i o n a l Parameters 1+7 p-Chloronitrobenzene 1 VII. P o s i t i o n a l Parameters -. 58 Acenaphthenequinone VIII. Transformations between Space Group and Projection Coordinates 67 IX. F i n a l Parameters 7I+ X. Bond Lengths and Valency Angles • . 75 XI. Molecular Orientation i n the Crystal 77 cis -1 ,2-Acenaphthenediol XII. F i n a l Parameters " 88 XIII. Bond Lengths, Valency Angles and Some Intramolecular Approach Distances 89 XIV. -Molecular Orientation i n the Crystal . . . : 91 cis -1 ,2-Acenaphthenediol Dinitrate XV. F i n a l Parameters 102 XVI. Bond Lengths and Valency Angles IO3 XVII. Molecular Orientation' i n the Crystal , 105 - x i -Page Comparison of Measured and Calculated Structure Factors A - l . Biphenylene hkO • 115 A-2. Biphenylene hkl I l 6 A-3. Methoxycarbonylmercuric Chloride hkO and Ok>fc . . ., 118 A-h. p-Chloronitrobenzene 0k£ and hO-i .' , 119 A-5< Acenaphthenequinone hkO and OkZ 120 A-6. cis-1 ,2-Acenaphthenediol hOJL 122 A-7. cis-1 ,2-Acenaphthenediol hlb 123 A-8. cis-1 ,2-Acenaphthenediol Dinitrate hoJl ; 125 A-9- cis-1 ,2-Acenaphthenediol Dinitrate hlJL 127 GENERAL INTRODUCTION - 2 -This thesis i s concerned with the'X-ray investigation of several compounds .of s t r u c t u r a l interest. I t i s divided into three parts. In Part I are presented some aspects of c r y s t a l symmetry and d i f f r a c t i o n theory, and an outline of present practice of structure determination "by X-ray,methods. The exposition i s necessarily b r i e f , and i s intended to serve as an introduction for the general reader. Part I I describes the refinement of the c r y s t a l and molecular structure of biphenylene, and the determination of the structure of methoxycarbonyl-mercuric chloride and p-chloronitrobenzene. Adequate computing f a c i l i t i e s were not available during the analyses of these compounds;,the structure factor calculations were performed on,a desk calculator, and Beevers-Lipson s t r i p s were used for Fourier summations. In the f a l l of 1961, an IBM 1620 computer was acquired by the UBC Computing Centre and shortly afterwards Dr. Ahmed's structure-factor and Fourier programs became available. I t was now possible to tackle structures of f a r greater complexity. A series of acenaphthene derivatives was examined, and the analyses of acenaphthenequinone, cis -1 ,2-acenaphthenediol, and c i s - 1 , 2 -acenaphthenediol d i n i t r a t e are described i n Part I I I . Structure factor tables for the various compounds are collected together i n Appendix I. Appendix I I i s a summary of the crystallographic data for trans-1,2-acenaphthenediol, trans-1,2-acenaphthenediol d i n i t r a t e , and several other organic compounds. PART I THEORY AND PRACTICE OF CRYSTAL-STRUCTURE ANALYSIS - h -I. ELEMENTARY CRYSTALLOGRAPHY A. Crystal Geometry Geometrical crystallography began when the relations between the plane faces of c r y s t a l s became a subject for investigation. I t was discovered by S t e n o i n 1669 that the angle between corresponding faces on c r y s t a l s of a pure substance i s always constant. I t i s thus the orientations, and not the sizes, of the faces that are cha r a c t e r i s t i c of the c r y s t a l . The faces of a c r y s t a l , and also planes within the c r y s t a l , can be described by reference to a set of crystallographic axes which may be any three non-coplanar edges of the c r y s t a l , or directions i n the c r y s t a l . Once 1 the choice of axes i s made, some face intersecting a l l three axes may be chosen as the parametral plane. I f a, b and c are i t s intercepts on.the c r y s t a l " axes, then i t i s found experimentally that the intercepts of any other face may be expressed as ma, nb, and pc where m, n.and p.are small integers or i n f i n i t y . This fact, known as the law of r a t i o n a l intercepts, was f i r s t enunciated by Hauy i n 1784. A given c r y s t a l plane i s commonly denoted by i t s M i l l e r indices (hk£), which are obtained by expressing the reciprocals of m, n and p as integers without a common di v i s o r . The M i l l e r indices are always small whole numbers for the well-developed faces of a c r y s t a l . According to the set of axes used to describe t h e i r faces, crystals are c l a s s i f i e d into seven systems. These are summarised i n Table I I . B. Symmetry of Crystals A geometrical figure i s said to possess symmetry i f , by performing on i t some movement or symmetry operation such as rotation about an axis, repeatedly i f necessary, i t can be brought into self-coincidence. The symmetry elements possessed by c r y s t a l s are l i s t e d i n Table I with the international symbols devised bv Hermann and Mauquin. - 5 -T a b l e I . S y m m e t r y E l e m e n t s o f C r y s t a l s 1 I d e n t i t y e l e m e n t 1 C e n t r e o f s y m m e t r y 2 T w o - f o l d r o t a t i o n a x i s 2=m M i r r o r p l a n e T h r e e - f o l d r o t a t i o n a x i s 7 T h r e e - f o l d r o t a t o r y i n v e r s i o n a x i s k F o u r - f o l d r o t a t i o n a x i s IT F o u r - f o l d r o t a t o r y i n v e r s i o n a x i s 6 S i x - f o l d r o t a t i o n a x i s 5" S i x - f o l d r o t a t o r y i n v e r s i o n a x i s H a s s e l i n 183O s h o w e d t h a t e x a c t l y 32 d i s t i n c t i v e c o m b i n a t i o n s o f t h e s e s y m m e t r y e l e m e n t s a r e p o s s i b l e . T h e s e c o n s t i t u t e t h e 32 c r y s t a l s y m m e t r y c l a s s e s , a l s o k n o w n a s t h e 32 p o i n t g r o u p s s i n c e t h e y a r e m a d e u p o f a s e l f -c o n s i s t e n t s e t o f s y m m e t r y e l e m e n t s w h i c h l e a v e s a t l e a s t o n e p o i n t o f t h e c r y s t a l i n v a r i a n t . T h e s y m m e t r y c l a s s e s m a y b e d i v i d e d i n t o s e v e n c r y s t a l s y s t e m s , ' e a c h o f w h i c h i s c h a r a c t e r i s e d b y t h e p o s s e s s i o n o f a m i n i m u m n u m b e r o f s y m m e t r y e l e m e n t s a n d r e f e r a b l e t o a s e t o f c r y s t a l l o g r a p h i c a x e s . T h e g e n e r a l a r r a n g e m e n t i s s h o w n i n T a b l e I I w i t h b o t h t h e S c h o e n f l i e s a n d H e r m a n n - M a u g u i n n o t a t i o n s . T a b l e I I . T h e 32 P o i n t G r o u p s o r C r y s t a l S y m m e t r y C l a s s e s S y s t e m L a t t i c e C o n s t a n t s C r y s t a l C l a s s e s T r i c l i n i c a / b ^ c 1 1 C l C i M o n o c l i n i c a / b ^ c o<=y=90°//3 ' 2 m=2 2/m C2 C $ C 2 h G r t h o r h o m b i c a / b / c o<=p=-tf=90)0 222 mm2 mmm D2 C2v D2h T e t r a g o n a l a = b ^ c o<=p=V=90o k £ k/m 1+22 1+mm 52m l+/mmm T r i g o n a l ( R h o m b o h e d r a l ) a=b=c ^=(3=^/90° 3 3 C 3 C 3 i 32 3m Im D 3 C 3 v D ^ d H e x a g o n a l a = b / c <*=p=90°, V=120° 6 6 6/m C 6 c 3 h c 6 h 622 6mm %ra2 6/mmm »6 C6 V D 3 h D 6 h C u b i c a=b=c (*=p=Y=90° 23 m3 T ^ 1+32 F3m m3m 0 T a 0 h - 6 -1 TMCUNIC 2 SIMPLE MONOCLINIC 3. SIDE-CENTERED MOMOCLINIC Vzy Yuy Mz^ 4 SIMPLE 0RTHORH0MBIC S END-CENTERED ORTHO RHOMBIC 6 FACE-CENTERED ORTHORHOMBIC 7 BODY-CENTERED ORTHORHOMB'C y-8 H6XAGOMAL 9 R H O M B O H E D R A L 10 SIMPLE TETRAGONAL 11 BODY-CENTERED TETRAGONAL £ Z 7 1/ -A-12. SIMPLE CUBIC 13. BODY-CENTERED CUBIC 14 FACE-CENTERED CUBIC Figure 1. Tlie 14 Bravais l a t t i c e s . C Space Lattices The characteristic geometrical form and external symmetry of a c r y s t a l •point to a regular in t e r n a l arrangement i n which a certain unit of structure i s repeated i n f i n i t e l y i n space "by regular translations. The arrangement of the c r y s t a l units may he represented by an orderly three-dimensional array of points known as a space l a t t i c e . The l a t t i c e points represent the positions occupied by the repeating unit of the c r y s t a l pattern, composed of atoms or groups of atoms. Connecting the l a t t i c e points by a regular network of l i n e r esults i n a number of i d e n t i c a l p a r a l l e l - s i d e d unit c e l l s . The choice of a unit c e l l for a given space l a t t i c e i s dictated by considerations of convenience i n v i s u a l i z i n g the symmetry and carrying out mathematical calculations. Obviously the space l a t t i c e i s completely defined by the three non-coplanar vectors representing the unit c e l l edges. These three basis vectors,•usually denoted by a, b, and c", are also referred to as the primitive translations of the l a t t i c e . In lQk& Bravais showed that there are Ik d i s t i n c t space l a t t i c e s . Unit c e l l s of the lh space l a t t i c e s are i l l u s t r a t e d i n Figure 1. D. Space Groups Since the atomic or molecular arrangement of a c r y s t a l i s based on an i n f i n i t e r e p e t i t i v e pattern, the symmetry operations may e n t a i l translations. Combination of rotation axes and r e f l e c t i o n planes with translations produce two new types of symmetry elements termed screw axes and glide planes -respectively. The possible groups of symmetry operations of i n f i n i t e figures are c a l l e d space groups, and t h e i r t o t a l number was shown to be 230 independently by Fedorov, Schoenflies, and Barlow i n the l a t t e r part of the l a s t century. A detailed account on space-group notation and nomenclature i s presented i n Vol. I of the International Tables for X-Ray Crystallography ( l ) , where diagrammatic - 8 -and analytic representation of the space groups are also given. The space group expresses the sum t o t a l of the symmetry properties of a c r y s t a l , and therefore cannot he established uniquely by a study of external form alone. The basis for space-group determination by X-rays i s that the translations of glide planes and screw axes, and the l a t t i c e centering present i n non-primitive l a t t i c e s , lead to the extinction of chara c t e r i s t i c types of X-ray spectra. Unfortunately t h i s determination i s not always unique as, due to Friedel's law, a centre of symmetry i s added to the structure i n taking the d i f f r a c t i o n pattern. I t i s possible, however, to i d e n t i f y the correct space group among several p o s s i b i l i t i e s from a s t a t i s t i c a l analysis of the in t e n s i t y d i s t r i b u t i o n (2), and from other physical tests such as pyro- and pie z o e l e c t r i c measurements. I I . DIFFRACTION OF X-RAYS BY CRYSTALS •A. Scattering of X-Rays by Electrons and Atoms ,An electron i n the path of an X-ray beam i s forced into o s c i l l a t i o n by the periodic varying e l e c t r i c f i e l d , and i t s e l f becomes a source of electro-magnetic radiation o f the same frequency and wave length. By t h i s process the electron i s said to scatter- the o r i g i n a l beam. In an atom the scattered waves from the several electrons combine, and the r a t i o of the amplitude scattered by an atom at rest to that scattered by a single electron i s c a l l e d the atomic form factor, designated f Q . Because of the f i n i t e size of the atom, interference can occur among waves scattered by different parts of the electron cloud, and f Q decreases with increasing Bragg angle 6. Mathematically, f Q i s related to the electron d i s t r i b u t i o n i n the atom by the formula \ f j Z s i n k r kTr r 2 d r , ( l ) f o = where k = l+7Tsin6/;\. and ^ i s the atomic wave function. Tables of f Q data have been computed for most common atoms and ions through th e o r e t i c a l calculations, and are conveniently tabulated as a function of sine/A. i n V o l . I l l of the International Tables(l). B. Conditions for X-Ray D i f f r a c t i o n Maxima Consider a p a r a l l e l beam of X-rays impringing on,a space l a t t i c e defined by the basis vectors j "aj_ j (i=l , 2 , 3 ) > The directions of the incident and di f f r a c t e d beams may be represented by unit vectors u Q and u which make angles je D. The Structure Factor In general,,the waves scattered in any order hkil by the atoms in a unit c e l l d i f f e r in phase and must be compounded vectorially. The resultant F(hkfL)is known as the structure factor and can be expressed as an explicit function of the fractional coordinates of the N atoms in the unit cell:-, 0 v 27Ti(hx.+ky.+ ez.) F(hke) = 22 f- e 3 (11) The complex quantity F(hk£),is characterised by an amplitude JF(hk&)| and a phase o<(hk€) • The structure-factor formula 11 is equivalent to the set of equations |F(hk€) cX ( h k t ) •+ B tan -1 B N •A= f, cos 2 Tr (hx.+ky ,+/z.) —' 0 J J J j = l N B = f j sin>2 7T ( h J C j + k y ^ + ^ Z j ) . J=l ,(12) J - 13 -In ci dent X - ray bea.m Figure 5- B i f f r a c t i o n . i n reciprocal space. In equations 11 and 12 the effect of thermal vibrations of the atoms i s taken into account through the r e l a t i o n -Bsin29/?£ f = f e o (13) .where the constant B i s equal to 8TT times the mean; square displacement of the atom i n a dir e c t i o n perpendicular to the r e f l e c t i n g plane. In practice B ,is treated as an empirical parameter and refined i n the course of analysis. E. The Intensities of X-Ray Reflections A c r y s t a l r e f l e c t s X-rays over a certain,angular range i n the neighbourhood of the Bragg angle, and when i t i s turned through the reflecting p o s i t i o n with an,angular v e l o c i t y to ,•different portions of the c r y s t a l are successively brought into the position of maximum r e f l e c t i o n . The r a t i o E ^ / l Q , where E i s the t o t a l energy reflected during a sweep,and I 0 the int e n s i t y of the primary beam, i s found to give-a correct measure of the - 14 -reflecting power of the crystal and is termed the integrated reflection. The majority of real crystals appear to have a mosaic block structure, in which tiny crystal fragments of linear dimension ~ 10"^ cm. are nearly but not quite aligned. For such a crystal block of volume oVDarwin and others have derived the following relation: 2 l»l B«v . ( a y ECO = / Ne2 V ~3 , l+cos 226 I„I2 , I V m c / 2 sin26 o \ / In equation lU the term e2/mc2 arises from the c l a s s i c a l formula for scattering by an electron, and N i s the number of unit cells per unit volume of the crystal. The trigonometric term takes two factors into account. The polarization factor ( l + cos 2 26)/2 allows for the p a r t i a l polarization of the reflected beam, while the Lorentz factor l/sin2© occurs because the reciprocal points pass through the surface of the reflecting sphere at different speeds. For application to crystal specimens expression 14 must be modified according to the' experimental conditions, which may introduce a different form for the Lorentz factor. For example, the intensity formula for the equi-inclination Weissenberg method i s E C O nWge A ( h k e ) [ F / 2 ( } I ^cos6 —*~ where ~% is the cylindrical coordinate of the reciprocal l a t t i c e point. The transmission factor A(hkt) ;is introduced to allow for absorption in the crystal, and has the form A = | e " ^ dV , (16) J V where t is the total path length of the X-rays reflected from an element dV, and jm and V are respectively the linear absorption coefficient and volume of the crystal. Evaluation of this integral i s in general d i f f i c u l t , - 15 -and values for specimens of simple shapes are tabulated as a function -of © in,the International Tables(l). Two other factors arise when the c r y s t a l does not conform to the i d e a l l y imperfect structure. The perfect block of the mosaic may be so large that the upper layers screen,the lower ones i n the same block an effect known as primary extinction, Secondary extinction refers to the screening of the lower blocks by the upper blocks. Both types of extinction cause a s i g n i f i c a n t diminution of int e n s i t y of the strongest r e f l e c t i o n s . Extinction corrections are usually neglected i n c r y s t a l -structure analysis, and are included only when t h e i r magnitudes are suspected of being large. F. Representation of the Crystal as a Fourier Series The periodic d i s t r i b u t i o n of electron density i n a c r y s t a l may be represented by a t r i p l e Fourier series oo oo oo ).= Y Y Y C(hk£)e h=-<*> k=-«° <£=-«> -27Ti(hx+ky+^z) The Fourier, c o e f f i c i e n t s C(hk£) can be readily shown to be equal to F(hk£)/V'. Thus OO oo oo j P(xyz) = i Y_. Y Y FChkXJe-^^+ky+tz) ' h= k= £= For convenience i n calculation the structure factor i s replaced "by i t s amplitude and phase. In, accordance with Friedel's law, | F(hk€.) | = JF(hk£.)| , so that equation 17 becomes oo o*» 9 (xyz) = f Y Y Y |F(hk£)| cos r27r(hx+ky+£z)-os(hke) . (18) h= k= -£= In a centrosymmetric c r y s t a l the value of the phase angle i s r e s t r i c t e d to - 16 -0 or IT ,. and so.the electron-density expression i s s i m p l i f i e d to OO oo oo 5>(xyz) = | Y Y Y - l F ( h k e ) | cos 2 7T(hx+ky+eZ) . (l£) h= k= e = G. The Phase Problem Equations 18 and 1 £ i l l u s t r a t e the 'phase problem' of X-ray crystallography. The structure amplitudes can be determined experimentally, but the r e l a t i v e phases are l o s t i n taking the X-ray pattern and must" be recovered by indirect means. An i n f i n i t e number of electron-density d i s t r i b u t i o n s may be obtained by assigning arbitrary phases to the structure amplitudes. However, the number of possible phase combinations i s greatly reduced by the requirement that f (xyz) must be everywhere non-negative and composed of spherically symmetric atomic functions, and that the structure postulated i s chemically reasonable. In f a c t , a set of phases which s a t i s f i e s the above c r i t e r i a i s almost c e r t a i n l y the correct one. Some of the more important methods of solving the phase problem are outlined i n section III-C. - 17 -I I I . THE DETERMINATION.OF CRYSTAL STRUCTURES A. Two-Dimensional Projections The summation of the t r i p l e Fourier series 18 i s extremely laborious. Furthermore the c o l l e c t i o n and calculation of a l l F(hkC)1s involve a great deal of work. I t i s usual therefore to project the structure onto two or more a x i a l planes using a double series, which can be computed from zonal data of the type F(hkO). Except for very complex structures, two-dimensional projections are s u f f i c i e n t to y i e l d a f a i r l y accurate set of atomic coordinates, expecially when special precautions to eliminate errors are taken (section III-D). B. The Interpretation of D i f f r a c t i o n Patterns The determination of the s p a t i a l relationships of the-atoms i n a c r y s t a l proceeds i n f i v e stages: (a) Determination of Unit C e l l 1 Parameters and the Space Group. (b) Collection of Intensity Data. (c) Determination of the Structure. (d) Refinement of Atomic Parameters. (e) Assessment of Accuracy. Stages (a),and (b) constitute the routine part of a crystal-structure investigation, and are described i n d e t a i l i n a number of treatises(3)• In the paragraphs that follow, stages (c), (d) and ( e ) a r e given a b r i e f discussion. C. Methods for Obtaining an Approximate Structure The various methods for solving the phase problem are conveniently c l a s s i f i e d into three categories; i n general no one method i s certain to lead to the correct structure. (a) T r i a l and Error Methods. In these methods crystallographic, physical and chemical 1knowledge are combined to arrive at a t r i a l structure which gives - 18 -reasonable agreement between the observed and calculated structure amplitudes. A good indication of the correctness of the postulated structure i s that the about 0.5. and 0.4 for centrosymmetric and non-centrosymmetric space groups respectlvely ( 4). Leaving out terms for which agreement i s poor, the calculated phases and the measured amplitudes are used i n a Fourier synthesis, which leads to a revised set of atomic coordinates. This i t e r a t i v e process i s repeated u n t i l a l l observed reflexions can be included i n the series summation. (b) Heavy-Atom and Patterson Methods. I f the c r y s t a l contains an atom of high scattering power situated at a known position, i t may determine a s u f f i c i e n t number of phases for a Fourier synthesis to reveal the l i g h t e r atoms. Sometimes i t i s possible to replace such a heavy atom by another at the same posi t i o n without disturbing the essential nature of the structure, so that the phase relationships can be determined from a difference effect. The heavy-atom and isomorphous replacement methods are b e a u t i f u l l y exemplified by Robertson's determinations of the structures of the phthalocyanines(5). In an organic structure the position of the heavy, atom i s rarely f i x e d by symmetry,. and a general method i s needed for i t s location. • In 193^ + Patterson(6) showed that the function which can be computed d i r e c t l y from observed data, represents a density d i s t r i b u t i o n such that the vectors from the o r i g i n to the maxima correspond to vectors between a l l possible pairs of atoms i n the c r y s t a l . Systematic procedures have been developed to derive the atomic positions from t h i s vector d i s t r i b u t i o n ( 7 ) . The weight of a Patterson peak i s the product of the atomic numbers of the two atoms involved, so that the method can be discrepancy factor, defined as R -5J|F 0| - I Fc|| / X j F o | > should be (20) - 19 -applied most successfully to structures containing heavy atoms. (c) Direct Mathematical Methods. These methods seek to determine the phases d i r e c t l y from the structure amplitudes alone. • The Harker-Kasper i n e q u a l i t i e s ( 8 ) , derived by application of Schwarz and Cauchy i n e q u a l i t i e s to modified structure amplitudes, impose certain r e s t r i c t i o n s on the phases due to c r y s t a l symmetry. Further developments (9)> based upon the l i m i t i n g conditions that j?(xyz) ^ 0 and i s a superposition of discrete atomic functions, furnish completely general systems of i n e q u a l i t i e s as v e i l as e q u a l i t i e s . Sign relations- between structure factors i n centrosymmetric space groups have been derived by Sayre(lO), Cochran(ll), and Zachariasen( l2) . The l a t e s t development -i s the s t a t i s t i c a l approach of Hauptmann and K a r l e ( l 3 ) , which provides expressions for the p r o b a b i l i t y of a .structure factor being pos i t i v e or negative. D. Refinement Procedures The' p r i n c i p a l methods for crystal-structure refinement are outlined i n the following sections. (a) F Q Synthesis. Atomic parameters obtained from successive Fourier synthesis are affected by ( i ) errors i n c e l l dimensions; ,(ii),inaccurate F D values; ( i i i ) round-off errors i n computation; (iv).termination of the Fourier series, while the remaining c o e f f i c i e n t s are s t i l l appreciable; and (v) thermal motion of the atoms. The d i f f e r e n t i a l synthesis of Booth(lU), which locates the atoms exactly at the electron-density maxima, i s subject to the same sources of error. The effect due to series-termination i s serious; i t may be allowed for by computing,a F c synthesis separately and applying back-shift corrections to the-atomic coordinates (15). (b) Method of Least Squares. This procedure was f i r s t used by Hughes(l6) to f i n d the atomic parameters which give the best f i t to the set of F ' s . The function minimized i s ^ w ( | F Q| - | F c | ) , where w i s a weighting factor. To each observed r e f l e c t i o n there corresponds an observational equation,, and the set of equations can be normalised and solved for the coordinate s h i f t s . Refinement by'least squares i s free from series-termination errors; i t i s also •possible to include i n d i v i d u a l isotropic or anisotropic temperature factors and a scale factor i n the refinement process, (c) Difference Synthesis. The function 1 oo OO B=5b"-Pc = V Yl E E ( ' F ° I " l F c l ) c o s [ 2 7 ^ ( h x + k y + ^ ) - o < ( h k e ) J (21) , h= k= 1 = -OO — oo — oo was f i r s t suggested byBooth ( l 7 ) as a device for refinement .and i t s properties were f u l l y exploited by Cbchran(l8). An, atom of the proposed structure which deviates s l i g h t l y from i t s tree'position l i e s on a steep slope of the difference map. From Figure 6 i t i s clear that the.atom should be shifted up-the gradient. The displacement i s given by A r /hi c>D '/*r (22) 'A r 2 -fur' where i s a constant i n the approximation jp = £0 Q, ' " for the electron density at a distance r from the centre of an atom. Refinement by (F 0-F c) synthesis automatically eliminates series-termination e r r o r s ; , i t furnishes valuable information about the thermal motion of the-atoms, and can be used 1 i to locate hydrogen atoms Figure 6. Effect of a email error- i n atom location on D. - 21 -(d) Generalised Projections. Frequently only one clear projection of a structure, say, on (010), can be obtained. Without u t i l i z i n g the complete (hk€)"data, approximate y-coordinates can be deduced from the Kth layer data by the method of generalised projections due to Cochran,and others(l9)< The expression for a structure factor belonging to the Kth layer i s p(hKfc) = X { f j ( h K ^ e 2 1 r i K y j } e 2 l r 1 ( h x J + g z j ) . j When the zero and'Kth layers are close together, f . ( h K o ) ^ f.(hO&) so that the 3 3 generalised projection 5K ( x z ) = i E £ F ( h K e ) e " 2 7 r i ( h x + e z ) h= 1= — oo — O O = C K(xz) + i S K(xz) ,(23) represents a projection of the structure on (010), with the electron density at ,the j t h atom modified by a factor e^TTiKy^ _ Q Q s 27rKyj.'+ i sin 2^Kyj . Thus yj can be deduced from 277"Kyj = t a n - 1 Sj^/Cj^ . Elimination of series termination errors can also be achieved by the use of (F 0-F c) Fourier c o e f f i c i e n t s . The res u l t i n g difference cosine and sine D D generalised projections, and S^- , are used to refine the x, y, z and B parameters simultaneously i n the following expressions (20): ?K,o s i n277"K(y 0-y c) /= s£ .cos27?-Kyc - c£ s i n 2 ^ K y c , (2J+) A r = ^ s i n 2 ^ c + CK C 0 s 2 ^ K y c V 2 ^ ? K , o , (25_) t?YL,o cos277-K(y 0-y G)- fK,c = S K sin27TKyc. + C^ cos27^Ky c . (26) - 22 -E. Assessment of Accuracy Crui'ckshank,. among others,,has investigated the standard deviation i n the electron density and i n atomic positions ( 2 l ). His results are < r ( * o ) . - i { E m i - I * ! ) 2 } * and C7j(x) = 2 7Ts h 2( [F0|- iF cj) 2 Ji/aVC J : (21) (28) with s i m i l a r expressions for the y and z coordinates. Here s has values 1 and 2 for centrosymmetric and non-centrosymmetric structures respectively, and j x = -\2 . p C i v = °S'^I ^ x i s t l i e c u r v a t u r e at the centre of the j t h atom The standard deviation of the bond distance between two atoms i s given by the r e l a t i o n o . o o (29) 0" 2(d i 2) = o\ + where and CTg are the standard deviations of the positions of the atoms i n the direction of the bond. Two bond lengths measured as d^ and dg d i f f e r i n g by an amount h w i l l have a p r o b a b i l i t y P = ;rf (-2 2 , 2 ^ . 0" — 0~ +• CT* •J i AB A B (30) y i r C?AB of being observed d i f f e r e n t l y because of experimental errors. Cruickshank(2l) has suggested the following subdivision of significance: Comparison of S and CT*^ g P Significance of observed bond length difference S £1.645 CAB 5$ ,or greater not s i g n i f i c a n t 1 . 6 4 5 ^ 6 4 2 . 3 2 7 0 ^ 5$ - 1* possibly s i g n i f i c a n t 2 . 3 2 7 0 * ^ ^ 3 . 0 9 0 crm ,1$ - o.vf, s i g n i f i c a n t 3.090 (7-^ > 6 .0.1 or less highly s i g n i f i c a n t -•23 -The standard deviation of an angle ©, .between two bonds d-j_2 and d 2 3 is given.by 2 » / \ * J ^ 3 2 V \ 2 d ^ 2 3 + d 2 ^ • ^ PART II THE CRYSTAL AND MOLECULAR STRUCTURES OF • BIPHENYLENE, METHOXYCARBONYLMERCURIC, CHLORIDE,, AND p-CHLDRONITR0BENZENE - 25 -I. BIPHENYLENE . A. Introduction The structural formula ( l ) , o f t h i s hydrocarbon was f i r s t given in ,1901 by Niementowski(22), who used the name biphenylene. This name i s now-adopted by most American chemists, although European workers .generally prefer the name diphenylene. The carbon atoms are numbered as shown i n formula"(I). Biphenylene'is of interest to'both.theoretical and organic chemists since - i t i s the only stable derivative of the elusive cyclobutadiene. The synthesis, chemistry and structure of t h i s unusual compound have been the subjects of many studies, and several reviews have been published (23)< Synthesis. Genuine biphenylene was f i r s t synthesised by Lothrop(24) i n 19^1 by the d i s t i l l a t i o n of 2,2'-diiodobiphenyl ( l l ) or biphenylene-2,2'-iodonium iodide ( i l l ) with cuprous oxide. This synthesis has since been improved (25),and several other methods of preparation,are now available (26), of"which the most interesting i s that due to Wittig and Pohmer. They showed that o-bromofluorobenzene reacted with l i t h i u m almalgam i n ether to give biphenylene and triphenylene(lV) with yeilds of 2U$ and 3$ respectively. The reaction i s - 26 -thought to proceed v i a the reactive•intermediate benzyne (V). The Structure of Biphenylene. As evidence for the s t r u c t u r e • ( i ) , Lothrop c i t e d a n a l y t i c a l data for the hydrocarbon and i t s p icrate, molecular weight determinations i n benzene and i n camphor, oxidation.to phthalic acid by chromic acid, reduction to biphenyl by hydrogenation over red-hot copper, and formation of the same compound, namely 2,7-dimethylbiphenylene (VT), by the pyrolysis of both 5,5"-dimethyl. (VIl).and 4 , 4 '-dimethyl (VIII)-biphenylene -2,2'-iodonium iodides. However, i t was soon pointed out by Baker (27) that such evidence did not exclude -the p o s s i b i l i t y that ,the hydrocarbon was actually benzopentalene (lX),.the formation of which could be explained by (VII) (VI) (VIII) assuming a fre e - r a d i c a l mechanism. • This view was supported by Coulson(28) who deduced that the s t r a i n energy of biphenylene was much higher "than'that, of benzopentalene (~ 100 versus a few kcal./mole), while the resonance energies were about the same (90 and 86 kcal./mole, respectively). The structure was f i n a l l y settled i n 19^ 3 by the electron d i f f r a c t i o n studies of Waser and Schomaker(29)> which established the dibenzocyclobutadiene formulation conclusively. Further confirmation of the structure was provided by an X-ray crystallographic analysis by Waser and Lu(30). These str u c t u r a l determinations - 27 -indicated that the C-C bonds in,the six-membered rings had an average length o of 1.39 A, and that the bonds joi n i n g these rings were s i g n i f i c a n t l y "longer f i n e r d e t a i l s of bond-length v a r i a t i o n i n the molecule. Cyclobutadienoid Character. Despite the very considerable angular s t r a i n , the four-membered rin g i n biphenylene • i s remarkably i n e r t towards a variety of reagents, and can be cleaved only by c a t a l y t i c reduction. • Biphenylene undergoes many of the t y p i c a l aromatic substitution reactions, including n i t r a t i o n , sulphonation, halogenation, mercuration, acetoxylation, and the Friedel-Crafts, reaction ( 3 l ) - Monosubstitution occurs exclusively at posi t i o n 2, i n agreement with the the o r e t i c a l predictions of Brown(32).and of Fernandez Alonso and Domingo(33)- Experiments on disu b s t i t u t i o n of biphenylene (31) have shown that a meta-directing substituent such as the acetyl group (x ) at position 2 directs the second substituent into position 6 by a resonance effect involving both six-membered rings, and i t appears therefore that there i s some cyclobutadienoid character about the central four-membered ring. measurements were n o t • s u f f i c i e n t l y accurate to detect the Positions l,3>5>7,are deactivated; position 6 i s (3 , and hence more reactive than position 8 which i s oi . 5 (X) 4-Interaction between the outer rings i s also indicated'by "the-ultraviolet spectrum (3*0> which shows two main regions of absorption: a high-intensity band at 235-260 mu. corresponding to the lone intense band of biphenyl at 250 mi - 28 -and a second band of lower in t e n s i t y i n the region 330-370 mu attributable to some conjugation between the rings. Molecular centre of symmetry shown by X-ray c r y s t a l data. On the other hand, recent attempts to prepare 7"r-complexes of biphenylene (35) have succeeded only i n getting the benzene type such as p-biphenylenebis(tricabonylmolybdenum);(Xi). The a b i l i t y of biphenylene to form .coordination.compounds using each six-membered ring independently, but not the four-numbered r i n g system, i s consistent with the preferred' bond structure ( X l l a ) i n which there i s l i t t l e or no.cyclobutadienoid character i n the central ring. The foregoing evidence provides di f f e r e n t answers to'the question regarding the extent of interaction between the benzene rings. A direct and more quantitative measure of cyclobutadienoid character i n biphenylene would be the mean' length of the central bond 9-10, but unfortunately the uncertainty in,the value 1.46+0.05^ determined by electron d i f f r a c t i o n (29) makes i t •difficult-to•draw d e f i n i t e conclusions. Bond Structure. For biphenylene f i v e Kekule structures may be drawn, one of which ( X l l a ) r e p r e s e n t s i t as a derivative of cyclobutane, two(XIIb and XIIc) as a cyclobutene, and two•(Xlld and XIIe),as a cyclobutadiene. Simple resonance theory,-with the f i v e canonical forms contributing equally to the - 29 -8 5 (a) 00 .(c) (e) (XII) hybrid molecule, shows that the 1-2 bond has more double-bond character than the 2-3 bond, and hence an ortho,para-activating group'in position 2 should direct.an entering substituent into position 1. This prediction i s at variance with that drawn from molecular-orbital calculations which indicate that the second substituent should be directed into position 3 (3^)- Recently i t has been shown that bromination of 2-acetamidobiphenylene gives 2-acetamido-3-bromobiphenylene (37)* and that 2-aminobiphenylene couples with benzenediazonium chloride at the 3-position (38)- In valence-bond terminology these results imply that the preferred Kekule- structure of biphenylene i s Since the two theories also predict different bond-length variations f o r biphenylene, i t should be possible to decide between them by an accurate measure of the bond distances. The present research i s concerned with the determination of these distances by a detailed X-ray examination of the c r y s t a l l i n e material. A l l the cr y s t a l s i n the o r i g i n a l sample of biphenylene were twinned on (lOO), but well-formed single crystals were obtained by r e c r y s t a l l i z a t i o n from propan-l-ol ( c f . r e f . 3 0 ) . These consisted of pale yellow prisms elongated along the c-axis. The density was determined by f l o t a t i o n i n aqueous potassium iodide. The u n i t - c e l l dimensions and space group were determined from rotation.and o s c i l l a t i o n photographs of cr y s t a l s rotating about the b- and c-axes, hC"6 , hkO, h k l , and hk2 Weissenberg films. No ( X l l a ) . B. Exp erimental - 30 -precautions were taken to prevent the c r y s t a l v o l a t i l i z i n g , so that they disappeared i n a few days. Crystal Data. Biphenylene, • C^Hg; M=152.2; m.p.llO°C. Monoclinic, a = 19.66+O.O6, b=10.57+0.04, c=5.85+0.01A, j5 =91.0+0.50. U=1215-5A . D x(with Z=6) = 1 .240, Dm=l.24g.cm73 Absorption c o e f f i c i e n t for X-rays, 7v =1 .54l8A, jj =6.46 cmT1 F(000)=480. Absent spectra: hOE when h i s odd, OkO when k i s odd. Space group i s "22^/ a-C^ . The i n t e n s i t i e s of the hkO and hkl reflexions were recorded on Weissenberg photographs f o r a c r y s t a l rotating about the c-axis, the equi-i n c l i n a t i o n method being used for the-upper l e v e l . CuK^ radiation was used, with m u l t i p l e - f i l m technique (39) to correlate strong and weak reflexions. The i n t e n s i t i e s were estimated v i s u a l l y , the range being about 5000 to 1. The values of the structure amplitudes were derived by the usual formulae for a mosaic c r y s t a l , the absolute scale being established l a t e r by correlation with the calculated structure factors. No-absorption corrections were applied. 65 independent hkO reflexions with h=3n were observed (see below for discussion of "h=3n rule"'), representing 71$ of the t o t a l number of these reflexions t h e o r e t i c a l l y observable with CuK^ radiation, but only 36 very weak reflexions with h / 3 n were observed (about 20$ of the possible number). 206 hkl reflexions were recorded, representing about 40$ of the possible number observable. C. Structure Analysis [OQl] Projection Since there are six molecules i n the unit c e l l , two of them must be situated at centres of symmetry at 000 and -^g-0, and the other four i n general positions. As pointed out by Waser and Lu ( 3 0 ) , the hkO reflexions exhibit a d i s t i n c t i v e feature, being very weak unless h=3n, and - 31 -t h i s "h=3n r u l e " requires that to a f i r s t approximation the atoms are grouped i n threes with coordinates (x,y,z), ( i + x,y, r+z'), ( i - x , y , r-z')> where z'= + z, and r i s the z coordinate of the centre of a molecule which i s i n a general position. Waser and Lu obtained values for a l l the parameters from a consideration of the molecular Fourier transform, and from various t r i a l s . Structure factors were calculated for the hkO r e f l e c t i o n s with h=3n (those with h^3n necessarily, have zero calculated value), by using the x and y parameters given by Waser and Lu, with the scattering factor for carbon of Berghuis e_t _al(l+0), with B=U.8^2. The discrepancy factor for the observed reflexions was R=0.20U. Refinement proceeded by computing Fourier and difference syntheses, and adjusting the positional'parameters. After one cycle R had been reduced to ' ' 0 . 1 8 2 . Further refinement then required consideration of planes f o r which h^3n. The*"h=3n r u l e " had been very useful i n establishing the corrfect t r i a l structure i n the f i r s t instance,,but at t h i s stage of the analysis i t proved troublesome, since i t was very d i f f i c u l t to decide-just what the small deviations of atomic positions were which gave rise-to'the observation of hkO reflexions with h/3n- These r e f l e c t i o n s were a l l so weak that i t was impossible to deduce from the.magnitudes of these structure factors what small displacements were involved. Refinement of the hkO data was therefore terminated at "this point, and attention was turned to the h k l zone i n which there are no systematically weak reflexions. The p o s i t i o n a l parameters at t h i s stage of the analysis are l i s t e d i n the second and t h i r d columns of Table I I I , and,the measured structure factors, F 0 , are compared with the calculated values, F c ( l ) , i n Table A - l (R= 0 . l 8 2 ) . An electron-density projection along the c-axis, computed with measured structure amplitudes and calculated signs for h=3n reflexions only, i s shown i n Figure 7-- 32 -W-1 y i H J & • H J (c\T) (CM ro CM O F i g u r e 7. (a) E l e c t r o n - d e n s i t y p r o j e c t i o n a long [ o o i ] , computed w i t h h=3n p l a n e s o n l y . Contours at i n t e r v a l s of 1 e . i " 2 , with, the one e l e c t r o n l i n e b r o k e n . ("b) Numbering of the carbon atoms. - 33 -hkl Refinement Since no resolution of the in d i v i d u a l atoms could be expected i n projections down,the a- and b-crystal axes, the problem of finding the z coordinates and of r e f i n i n g the y. and x parameters further was approached by considering the hkl structure factors. Structure factors were calculated f o r these reflexions by using the x,y and B parameters from the hkO refinement and the z coordinates given,by Waser and Lu. The discrepancy factor was 0.2U8. Refinement proceeded by computing cosine and sine'difference generalised projections, r e f i n i n g a l l three p o s i t i o n a l parameters x, y, z, and the - isotropic temperature-parameters,Y, Z1 are coordinates o expressed in A and referred to orthogonal axes a, b , and c'. The equations of these mean molecular planes are: Molecule I (atoms C^-Cg and c]_-Cg): 0.6109X' + 0.6353Y + 0.4718Z' = 0 . Molecule II (atoms Cy-C^) 1 ' 0.6035X' + 0.6582Y - 0.1+500Z1 - 2.8008 = 0. The deviations of the atoms from these planes are l i s t e d in the last column of Table III. The bond lengths and valency angles, calculated .from the f i n a l x,y,z coordinates of Table III, are shown in Figure 8. The mean values of the distances and angles, with symmetry mmm assumed (this assumption is discussed below), are shown in Figure 9-M Figure 9- Mean bond distances and valency angles. - 37 -The orientations of the molecules in the crystal are given in Table IV, "here % L > fL, ^ <*>M. and ^ ^ ^ are-the angles which the molecular axes L, M (see Figure 9) and the-plane normals N make-with the orthogonal axes a,,b,, and c'. The axes L were taken through the molecular centre and the mid-point of bond 3-1+ for molecule ( i ) , and through the mid-,' pointsof bonds 9-10 and 15-16 for molecule ( l l ) ; and axes M through the molecular centre and the mid-point of 1-6', and through the mid-points of bonds 12-13 and 18-7. L, M, and N, are thus not accurately mutually perpendicular, the angles being ^04=90.6°, ^ ^ = 9 1 . 9 ° , and ALN=93.2° for molecule ( i ) , and 88.6°, 88.6°, SO.6° for the corresponding angles for molecule ( l l ) . The orientation angles d i f f e r from those given by Waser and Lu by a maximum of 5-3°> and a mean of 2 . 1 0 . Table IV. Orientation of Molecules in the Unit Cell Molecule Molecule Molecule Molecule Molecule Molecule ( I ) ( I D ' ( I ) ( I D ( I ) ' ( H ) 9 o L 1+0.90 37 .2 0 9 ^ M 90.9° 92.0° ?£ N 523° 127.1° y L — i22»i+° 117.90 — 55. xo 5 5 < 8 o y , N — 5 0.go i 3 1 . 2 ° (AL. ... 1 12 .1° 67-6° . . . H+5-l° 3^-2° cO r ... 61.8° 63.3° Standard Deviations The standard deviations of the atomic positions were calculated from Cruickshank's formulae. The mean values for a l l the atoms are 1.U2TA), ( 0 . 5 0 , I . 3 9 2 A ) , and (1 .00, 1.33c;A). This i s similar to the original correlation .curve given by Pauling(l+l) except for a small,change in the value used for the - 41 -single-bond distance. Coulson(42) ,has suggested that the usual 1.54A single-bond length observed i n diamond and i n al i p h a t i c molecules (sp^ hybrid s O orbitals),should be reduced to I.5OA i n aromatic molecules to allow for the change to sp 2-hybridization. Recent accurate measurements (43) of the -lengths of formally single bonds in.quaterrylene suggest, however, that the pure single-bond distance i n polynuclear aromatic hydrocarbons i s greater o than I.5OA , and the mean value f o r the s i x single bonds i n quaterrylene was therefor© ."uaad-inrderving 'the 'correlation curve- • There are marked discrepancies between these bond lengths predicted by the simplest resonance theory and those observed. The predicted lengths of bonds A, B, C vary i n the order long-short-long, and t h i s i s just the opposite of the measured order. Molecular-orbital calculations for biphenylene were f i r s t c arried out twenty years ago (29), and the calculated bond distances (model g) do not d i f f e r s i g n i f i c a n t l y from those (model h) of a more recent calculation (44). Model i_ has been derived from the calculated bond orders (44),by using a correlation curve passing through the usual points (O.525* 1.42-^ 5.)* (0.667* 1.392ft) 8 2 1 ( 1 ( l , 0 0 0 > 1.339ft)* e x t r aP°l a' t e C£.HgC02CH3+HC£ The structure of these compounds was in doubt for many years, although Schoeller (45) apparently proposed the correct structural formulation (XIIl) at an early date. The structure was not widely accepted because compounds of this type had been shown to yield carbon monoxide quantitatively by the action of methyl iodide or a dilute solution of hydrochloric acid. The carbon monoxide molecule thus appeared to be somewhat loosely bonded to the mercury atom, and this led to the suggestion of a structure (XIV") involving a coordinate link ( 4 6 ) . C l — H £ — C a — Wi \ \ (XIII) 0 • CH3 (xiv) x o»CH^ Further work (47) ,has f a i l e d to decide between,the two•alternative formulations, and structure (XIV) seems to have gained general acceptance ( 4 8 ) . Recent infrared and proton magnetic resonance measurements ( 4 9 ) , however, furnished results which correlated well with structure (XIIl),,and i t was f e l t - 44 -that an X-ray investigation of the cry s t a l s would establish the structure conclusively. The present X-ray analysis indicates that the true structure i s (XIII). B. Experimental Crystals of methoxycarbonylmercuric chloride are colourless needles elongated along the c-axis with the (100) face developed. The density was measured by displacement of carbon tetrachloride. The u n i t - c e l l dimensions and space group -were determined from rotation and o s c i l l a t i o n photographs of a c r y s t a l rotating about the c-axis, hkO .and h k l Weissenberg f i l m s , and 0k&, lk&,,h0t and hit precession films. Crystal Data. Methoxycarbonylmercuric chloride, CC.HgC02CH3; M=295.1; m.p.l07°C Orthorhombic, a=8.30+0.02, b=17.20+0.03, c=7.52+0.02A. U=107i|X3. D x ( v i t h Z=8) =3.64, £^=3. 58g.cm"3. Absorption c o e f f i c i e n t f o r X-rays, ?c =1.54l8&, u=6l0 cm7 A=0.7107&, 0=336 cmT1 F(000)=1024. Absent spectra: 0k£. when t i s odd, h0£when € i s odd,, hkO when (h+k),is odd. Space group i s Pccn — D^ The i n t e n s i t i e s of the•hkO reflexions were recorded on Weissenberg photographs, using CuK<^ radiation and multiple-films to correlate strong and weak reflexions. The 0k£, reflexions were recorded on precession films with related time exposures, using MoK^ radiation. A l l the•intensities were estimated v i s u a l l y , the range being about 4 0 0 0 . t e l . The c r y s t a l used was approximately c y l i n d r i c a l , 2 mm. in,length and 0.09 mm. i n diameter, and absorption corrections were applied for a c y l i n d r i c a l c r y s t a l . The structure -amplitudes were derived by the usual formulae,,the absolute scale being established l a t e r by correlation with the calculated structure factors. 69 hkO and 76 0k^ reflexions were observed, representing 68$ ,and 64$ -respectively of the possible numbers observable under the - experimental conditions. - 45 -C. Structure Analysis Inspection of the hkO photographs shows that reflexions with h=0,l+,8 are particularly strong while those with h=2,6,10 are either very weak or absent. Since the structure factor expression for these reflexions involves a term cos 2 7rhx, the mercury atom must have x coordinate approximately g . The 0k& intensities with k odd are also weak and few in number. Consideration of the term sin27r£. z in the structure factor expression leads to-the possible values z=0 or ^ for the mercury, atom. Patterson projections along the c- and a-axes (Figure l l ) confirmed the above conclusions and provided in addition coordinates for the-chlorine atom. The contribution of these atoms to the hkO and 0k& structure factors were calculated, the atomic scattering factors of neutral mercury and chlorine (50) being used. The signs of the majority of the structure amplitudes were correctly determined, except a few with small or no contribution from the mercury atom; for instance a l l 0k6 terms with k odd had to be omitted u n t i l the f i n a l stage of refinement. The f i r s t hkO Fourier synthesis was computed with 67 terms. The mercury atom .was well-resolved and had essentially the same-coordinates as provided by the Patterson projection on (OOl). The chlorine atom, however, moved appreciably and the electron-density distribution showed a linear concentration ,0 Q of peaks approximately 6A long, clearly separated- and lying at about 17 to the b-axis. It was obvious that the structure (XIV),must be rejected and the individual peaks corresponded to the carbonyl and methyl groups of structure (XIIl) The f i r s t Fourier synthesis for the a-axis projection was computed with 53 terms. This projection provided another view of the molecule arid confirmed the correctness of structure (XIIl). With the help of a ball-and-stick model, parameters for a l l the atoms were obtained by correlating both the a- and c-axes - he -Hg-a vector peak 0 1 2 3 4 5 k i . . . . i.... i I | I | Figure 11. (a) Patterson projection along [00l]. Contours are drawn at arbitrary i n t e r v a l s . (b) Patterson projection along [lOO]. Contours are drawn at ar b i t r a r y i n t e r v a l s . - U7 -projections. A second structure factor calculation was now carried out for the hkO and Oko reflexions. The temperature factor,< B=k.6A"^ for both zones, was obtained by p l o t t i n g m |"|FC| / | F Q| j , against sin 29. The discrepancy factor R for the observed hkO reflexions was 0.195 for mercury and chlorine only, dropping to O.153 when the l i g h t e r atoms were included;, the observed int e n s i t y of the 020 r e f l e x i o n was considerably lower than,the calculated value, probably because of extenction, and was omitted i n the evaluation of R. For 0k6 reflexions R was 0 . 1 6 9 ,for a l l atoms and 0.221 for mercury and chlorine only. Second Fourier syntheses for both projections were now computed, u t i l i z i n g a l l the observed structure amplitudes and t h e i r calculated signs. The electron density maps (Figure 12 and Figure 1 3 ),indicated e s s e n t i a l l y no change i n the mercury and chlorine positions, and only s l i g h t s h i f t s of the l i g h t e r atoms. A t h i r d structure factor calculation was not carried out.as s i g n i f i c a n t improvements were not expected by merely changing s l i g h t l y the positions of the carbon and oxygen atoms. The observed and calculated structure factors are compared i n TableA - 3 -Molecular Dimensions The f i n a l atomic coordinates, deduced from Figure 12 and Figure 13 and expressed as fractions of the unit-cell,edges,.are l i s t e d i n Table VT. The bond lengths and valency angles calculated from these coordinates are shown i n Figure . l h . Table VI. Positional 1Parameters Atom x y z Hg 0.1256 0.0203 0.2500 ce 0.1820 -O.O785 O.OU25 C"! O.O75 0.101 O.i+26 0-L O.O76 O.O95 O.588 o 2 0.069 0.169 0.373 -C2 -0.013 ,0.237 0,kk2 - 48 -v (t>) The structure viewed along [001]. -p-lliiillinl Figure 13. (a) Electron-density projection along [lOO]. Contours of the mercury atom are drawn at approximately 10,20,50,100,150 e.°T2, and other atoms at 8,10,15 e . X . (b) The structure viewed along [lOOJ. - 51 -Standard Deviations. The standard deviations of the atomic positions, calculated from Cruickshank's formulae, are Cr(x)= 0 r(y)= Cr(z)=0.007$. f o r mercury, 0 .0U4^ f o r , o chlorine, and 0.054A for carbon and oxygen. D. Discussion The resolution of the l i g h t e r atoms, especially the carbonyl group, i s not very good, p a r t l y because of overlap i n the projections, but c h i e f l y due to the dominating effect on the scattering of the heavy mercury atom. Both projections however indicate unambiguously that the -true structure i s ( X I I l ) . The coordination around the mercury atom i s exactly l i n e a r , and i n addition a l l the-atoms i n the molecule, except the methyl group, l i e i n one plane, with equation 0.9824X + 0.1671+Y + 0.0830Z - 1.2392 = 0 , where X, Y,-Z are coordinates expressed i n %. The methyl carbon atom i s o displaced from t h i s plane by O .39A. The Hg—Cl bond length (2 .35A, O-=0.0UA) and the Hg—C distance (1.96%, o. (7" =0.05A) do not d i f f e r s i g n i f i c a n t l y from the values reported for corresponding distances i n related structues ( 5 l ) - The other bond lengths and valency angles have been determined only rather imprecisely, but do not d i f f e r s i g n i f i c a n t l y from the normal values. The packing of the molecules i s i l l u s t r a t e d i n Figure 15• There are two short intermolecular distances, a Hg....C£. separation of 3'21A", and a Hg.... 0.(carbonyl) contact of 3-01^- These distances are however very similar to corresponding contacts i n c r y s t a l l i n e mercuric chloride (52), i n which the mercury atoms are surrounded by two chlorine atoms at distances of 2.25A" (bonded distances), two a t , 3 . 3 ^ , and a further two at 3-63^- The distances i n methoxycarbonylmercuric chloride are quite similar. A l l the other contacts are considerably longer, the shortest Hg.'. ..Hg distance being 4.29A\ - 52 -III. p-CHLORONITROBENZENE A. Introduction A preliminary, investigation of the crystal structure of p-chloronitro-benzene by Toussaint(53).indicated that the absent reflexions corresponded to space group P2]_yc (interchanging his"a~and c-axes),,and the measured density to two molecules in the unit c e l l , necessitating a molecular centre of symmetry. Two types of structures were considered possible: ( i ) , a disordered arrangement of molecules in space group P2]_/c, giving a s t a t i s t i c a l l y centrosymmetric structure, or ( i i ) an ordered.arrangement in space group P,c which gives weak reflexions when k i s odd. Arrangement ( i i ) was considered more lik e l y , and a structure based on space group Pc. was deduced from consideration of a few structure factors (which were not listed). The present investigation was made to establish the correct structure, and the-analysis described .below suggests that the true space group' is P2-jyc and that a disordered arrangement of molecules exists in the crystal. B. Experimental Crystals of p-chloronitrobenzene (Eastman Kodak), obtained by crystallization from ethanol, are colourless needles elongated along the a-axis with the (OlO) face developed. The density was measured by flotation in aqueous potassium iodide solution. The uni t - c e l l dimensions and space group -were determined from rotation and oscillation photographs of a crystal rotating about the-a«axis, Q k t and lk& Weissenberg films, and hkO and h O t precession films. Crystal Data. p-Chloronitrobenzene, CgH^N02CL ;M=157.6; m.p. 8 3 . 5°C Monoclinic,.a=3.84+0.01, b=6 .80+0.01, c=13-35+O.02A, |3 = 9 7 ° 3 1 ' + 5 '. U=3^5.6A3. Dx(with Z=2)=l.514, Dm=1.52 g.cm r Absorption coefficient for X-rays, X=1.5^l8ft, jx=kh.l cm"} ; A . = 0 . 7 l 0 7 i , u=5.1 cm"} F(000)=l60. Absent spectra: 5 h0€ when £, i s odd, OkO when k is odd. Space group ,is P2-]/ c -C2h • - 53 -Crystals of p-chloronitrobenzene are highly v o l a t i l e at room temperature so that a c r y s t a l v o l a t i l i z e d completely i n a few hours. The c r y s t a l used for in t e n s i t y measurement was a needle about 3 rm- i - n length and 0.15X0.08 mm. i n cross-section. I t was sealed i n a thin-walled Lindemann-glass c a p i l l a r y . The i n t e n s i t i e s of the 0k£ reflexions were recorded on Weissenberg exposures for a c r y s t a l rotating about the a-axis, using CuK„< .radiation, and multiple-films to correlate strong and weak reflexions. The h06 reflexions were recorded on precession films with MoK^ radiation,-using multiple exposures f o r intensity correlation. The ranges of O k t and h0£ i n t e n s i t i e s -were about 36OO t o l and 1800 t o l respectively, the estimates being made v i s u a l l y . The, structure amplitudes were derived from the usual formulae, the absolute scale being established l a t e r by correlation with the calculated structure factors."' 57 independent 0k£. reflexions-and 35 h0& reflexions were observed,, representing. •* hQ% and hhi> respectively of the possible numbers observable under the experimental conditions. C Structure Analysis [lOO] -Projection The Patterson map (Figure l 6 a ) could be interpreted on the basis of both ordered and disordered structures, although the Ct-Cl interactions were much weaker than expected, suggesting that the ordered structure was less l i k e l y . Nevertheless a few structure factors were calculated using an ordered model, with atomic scattering factors from Tabellen zur Rontgenstrukturanalyse (50). The agreement-between.measured and calculated structure factors was rather poor, and the calculated values for OkO reflexions with k odd- were s i g n i f i c a n t l y larger than the maximum possible observed values. A disordered model was then set up, consisting of two h a l f molecules, superimposed so that the carbon atoms coincided, but with the positions of - 54 -CM r4 O P a t t e r s o n p r o j e c t i o n a long [ l O O ] . Contours are drawn at a r b i t r a r y i n t e r v a l s . Diagram of one molecule i s superimposed. P a t t e r s o n p r o j e c t i o n a long [oicQ. Contours are drawn at a r b i t r a r y i n t e r v a l s . Diagram of one molecule i s superimposed. (j F i g u r e 16. (a) the chlorine and n i t r o groups interchanged. Approximate correlation between measured and calculated structure factors was obtained, the temperature factor being apparently quite high, and the electron-density projection showed good resolution of the six-membered.ring and a.peak of the expected shape and height at the position of the overlapping chloring atom and n i t r o group (Figure 17)- New coordinates were obtained and the 0k6 structure factors recalculated,. a temperature factor B=8.5^ being obtained by p l o t t i n g In | |Fc|y/ |F 0| ^ against sin2©. The strongest reflexions had consistently high F c values, and these discrepancies were attributed to secondary extinction. An empirical correction,(5^),was applied .using the r e l a t i o n I _ = u+gl - 1 + JL I I Q where I = in t e n s i t y that would be observed i n the absence of secondary extinction, I Q = observed int e n s i t y , u = l i n e a r absorption c o e f f i c i e n t , g = constant. I was taken,to be equal to i t s calculated value I c , and a plot of I c / l 0 against I c gave a value of 0.00173^ f o r t h e r a t i o g/u. This procedure appeared to have some j u s t i f i c a t i o n since the corrected values of the 00& structure factors agreed with those obtained from the h o t MoK^ data. Measured and calculated structure factors are l i s t e d i n Table A - k (R=0.23)> both corrected ( i n parentheses) and uncorrected F Q values being given for the stronger reflexions. [OlOJ Projection The x coordinates of the atoms were deduced from the orientation,of the molecule i n the (010),Patterson projection (Figure l6b) and the h O t structure factors calculated. A Fourier series was summed and the resu l t i n g map-indicated small s h i f t s i n atomic positions. • Structure factors were recalculated 0 1 2 3 A- 5 A ' i i i 1 Figure 17. (a) Electron-density projection along | 100) . Contours are drawn at inte r v a l s o_2 o_2 of approximately 1 e.A , with the lowest contour at 3 e.A (b) The structure viewed along [lOO]. 0 1 2 3 4 5 A i l 1 L 1 18. (a) E l e c t r o n - d e n s i t y p r o j e c t i o n a long [ d o ] . Contours are drawn, at i n t e r v a l s of approximate ly 1 e.ft ." 2 , w i t h the lowest contour a t k e . A . (b) The s t r u c t u r e viewed a long [ d o ] . - 58 -o2 ( a n d a r e i n c l u d e d i n T a b l e A - 4 , R = 0 . 2 6 ) , a t e m p e r a t u r e f a c t o r o f B=8.5A a g a i n b e i n g i n d i c a t e d ; t h e o b s e r v e d v a l u e f o r t h e 102 r e f l e x i o n w a s c o n s i d e r a b l y s m a l l e r t h a n F c , p r o b a b l y b e c a u s e o f e x t i n c t i o n , a n d t h i s p l a n e w a s o m i t t e d i n e v a l u a t i n g R . A f i n a l e l e c t r o n - d e n s i t y p r o j e c t i o n i s s h o w n i n F i g u r e 18. T h e f i n a l p o s i t i o n a l p a r a m e t e r s o f t h e a t o m s , e x p r e s s e d a s f r a c t i o n s o f t h e u n i t c e l l - e d g e s , a r e l i s t e d i n T a b l e VII. T a b l e V I I . P o s i t i o n a l P a r a m e t e r s A t o m X y z O.376 0.340 0.142 0.343 0.312 0.130 o.4o4 0.277 0.097 0.425 0.444 0.097 C l 0.167 0.153 0.064 C 2 0.110 0.169 -0.038 c 3 -0.065 0.017 -0.102 D . D i s c u s s i o n T h e a g r e e m e n t b e t w e e n m e a s u r e d a n d c a l c u l a t e d s t r u c t u r e f a c t o r s i s n o t p a r t i c u l a r l y g o o d , p r o b a b l y b e c a u s e t h e m o d e l u s e d i s n e c e s s a r i l y a r a t h e r c r u d e o n e , a n d a s s u m e s t h a t t h e s i x - m e m b e r e d r i n g s o f t h e t w o o r i e n t a t i o n s c o i n c i d e e x a c t l y . T h a t t h i s i s o n l y a p p r o x i m a t e l y s o i s i n d i c a t e d b y t h e t e m p e r a t u r e f a c t o r , t h e h i g h v a l u e p r o b a b l y r e s u l t i n g f r o m a s m e a r i n g o u t o f e l e c t r o n - d e n s i t y a s a r e s u l t o f t h e d i s o r d e r , r a t h e r t h a n t o l a r g e • t h e r m a l m o v e m e n t s . I t i s a l s o q u i t e d i f f i c u l t t o d e t e r m i n e t h e s c a l e f a c t o r p r e c i s e l y , s i n c e s m a l l e r r o r s i n t h e s t e e p s l o p e s o f t h e p l o t s o f i n ( I F c l / 1 F o l } a g a i n s t s i n 0 p r o d u c e s i g n i f i c a n t c h a n g e s i n s c a l e . I n v i e w o f t h e s e d i f f i c u l t i e s a m o r e e l e g a n t m o d e l w a s n o t t r i e d , a n d t h e c o r r e l a t i o n b e t w e e n m e a s u r e d a n d - 59 -calculated structure factors was considered s u f f i c i e n t l y satisfactory to indicate that the disordered arrangement i s the.correct one. The absence of diffuse scattering on the films indicates that the two orientations must occur randomly throughout the c r y s t a l . In, p_-bromochloro-benzene (55),and 1-bromo-U-chlorocyclohexane•(56),similar disordered arrangements have been observed. In these structures the.interchangeable -atoms, chlorine-and bromine, are-of course very similar i n size and chemical behaviour. Although at f i r s t glance the chlorine atom and n i t r o group.in p-chloronitrobenzene appear to be rather different i n nature, closer study suggests that t h e i r sizes are not very different and that t h e i r electro-n e g a t i v i t i e s are si m i l a r , so that i t i s not surprising that the structure-is disordered. A direct test of the approximate equivalence of the two orientations i s provided by an examination of the packing of the molecules i n the c r y s t a l . Allowing every molecule to have either arrangement, i t i s found that there are several intermolecular distances below- the smallest being a C . . . . 0 contact of 3-35A; the approaches thus correspond to normal van der Waals interactions, so that both orientations apparently exist i n the.crystal with no undue st r a i n . The disorder prevents accurate determination of the molecular dimensions, but the bond distances and val'ency angles appear to be normal. The molecule i s at least approximately planar, but a twisting of the n i t r o group, out,of the plane of the aromatic ring, of the order of 1 0 ° - 2 0 ° would probably not be detectable. PART I I I X-RAY STUDIES ON SOME DERIVATIVES OF ACENAPHTHENE - 61 I. ACENAPHTHENE AND DERIVATIVES A. Introduction In I867, Berthelot(5 7),isolated a hydrocarbon of molecular formula ^12%0 f r o m coal tar and named i t acenaphthene. Structurally• i t may be regarded as a derivative of naphthalene obtained by fusion of a f i v e -membered ring into i t s angular position. The enumeration of the acenaphthene nucleus, which i s used for a l l the derivatives, follows the I.U.P.A.C. 1957 Rules (58). The structural formula (XV) assigned to•acenaphthene by Berthelot was based upon i t s synthesis from acetylene and naphthalene (59) and from 1-ethylnaphthalene (6o),by pyrolysis. The most .convincing evidence was the oxidation of the hydrocarbon to give acenaphthenequinone by chromic oxide and acetic acid, naphthalic acid .by potassium permaganate, and naphthalic anhydride-by chromic acid ( 6 l ) . ' As a consequence of the pioneering work of Berthelot, and p a r t i c u l a r l y of Graebe(62), the reactions of acenaphthene and i t s derivatives have been studied i n d e t a i l . For work p r i o r to 1921 the comprehensive review by Hahn and Holmes(63) should be consulted. Recent developments have been reviewed by Csizmadia and Hayward(6U). - 62 -B. The Structure of Acenaphthene Formula (XV), which shows a-CB^-CR^ bond'length of 2.k% (width of a •benzene ring) and i n t e r i o r angles of 120°.and 90° i n the five-membered ring, i s obviously not an accurate representation of the molecular structure of acenaphthene. Considerable modification of the geometry of the-peri-ring i s expected, but i t i s uncertain whether the-carbon skeleton would remain planar. Of p a r t i c u l a r interest i s the length of the al i p h a t i c single bond which i s under considerable s t r a i n , as are also the bond-length v a r i a t i o n and .angular d i s t o r t i o n i n the naphthalene nucleus. "Accordingly, several attempts have been made to determine the molecular structure of acenaphthene by an X-ray analysis of the c r y s t a l l i n e material. Acenaphthene c r y s t a l l i s e s i n the orthorhombic system; i t s u n i t - c e l l dimensions were f i r s t determined by Bragg(65)-in 1921. On the basis of the systematic extinctions (0k£, absent with & odd),Hertel and Kleu(66) decided 5 that the space group was Pcmm-I^ > ignoring completely the other two k 2 p o s s i b i l i t i e s , v i z . Pc2"m-C2v and Pcm2Q_-C2v • Strangely enough the same conclusion was reached seven years l a t e r by'Banerjee and Sinha(67), who then proceeded to solve the c r y s t a l structure using both X-ray and magnetic data. Their analysis revealed a planar molecule with" the unusual 1length of 2.01% for the CH2-CH2 .bond. Subsequently i t was pointed-out by Kitaigorodskii ( 6 8 ) that the true space group .was Pcm2-[_, on the ground that the other two space groups, v i z . Pcmm and Pc2m, are forbidden to hydrocarbons (69). He arrived at the correct structure from .packing considerations and by constructing the centrosymmetric electron-density projection on (OOl). The structure i s interesting c r y s t a l l o g r a p h i c a l l y . The four molecules i n the unit c e l l f a l l into two independent sets and occupy special positions: the inherent symmetry plane normal to the molecular plane coincides with the symmetry plane-in the c r y s t a l . The CH2-CH2 bond length therefore depends only on the y coordinate of one - al i p h a t i c carbon atom. From consideration,of the o OkO structure factors alone, Kitaigorodskii (68),deduced a value of 1.8A for t h i s distance. Later, using p a r t i a l hkO CuKrx, data collected by means of an ioni z a t i o n chamber,, he computed the electron-density projection along [OOl] and o obtained a CH2-CH2 bond length of 1.64+0.04A (70). Further refinement of the structure has been carried out by'Ehrlich(7l) using two-dimensional (F 0-F c) syntheses. The analysis reveals a planar molecule with dimensions as shown i n Figure 19a. Contrary, to previous claims, the a l i p h a t i c CH2-CH2 bond i s not significantly.stretch ed , i t s length'being . o 1.5^ +0•01^ A. The bond distances i n the aromatic part of the molecule are s t i l l very similar to those-in naphthalene -(Figure•19b),(72).and the s t r a i n i n the p e r i - r i n g i s relieved by d i s t r i b u t i n g the angular stress over the entire molecule. C Survey of Known Analyses of Acenaphthene Derivatives Several derivatives of acenaphthene have been axamined by X-rays; the results show that the acenaphthene skeleton i s e s s e n t i a l l y planar,.with large deviations from 120° i n the valency angles. Of the simple acenaphthene derivatives, only 5*6"-dichloroacenaphthene (Figure 19c) has been investigated (73)- The molecule i s s l i g h t l y non-planar as a result of severe s t e r i c hindrance between the chlorine-atoms. In pyracene (Figure 19d) a value-of 1-59+0.03A has been reported f o r the CH2-CH2 bond distance (74). The bond-lengthening i s possibly s i g n i f i c a n t , although the authors did not consider t h i s to be so. The s t r a i n i n 2,13-benzfluoranthene (Figure 19e) i s even greater than that i n acenaphthene. I t has been shown,(75) that the molecule-has the expected symmetry, and that the longest- bond i s that on the open side of the - 6k -1-54 F i g u r e 19. Mean "bond l e n g t h s and v a l e n c y angles m (a) acenaphthene, (b) naphthalene , (c ) 5 , 6 - d i c h l o r o -acenaphthene, (d) pyracene , (e) 2 . 1 3 - b e n z i l u o r a n t h e n e , and ( f ) 20 -methy lc l io lanthrene . five-membered ring. The structure of 20-methylcholanthrene (XVl), which contains the acenaphthene system, has been subjected to refined three-dimensional analysis (76) . The acenaphthene skeleton has almost symmetry, and i t s average dimensions are shown i n Figure 19f• (XVI) (XVII) The structure of an acenaphthylene-dimer (XVTl) has been established by a c l e a r l y resolved projection (77)- Details of the molecular dimensions for t h i s compound are not available. F i n a l l y , crystallographic data have been -published for the following compounds ( 7 8 ) : 5-acetylacenaphthene, 3-acetylacenaphthene, 5>6-dibromoacen-aphthene, and oC -(5-acenaphthyl)ethylamine. I 1 - 66 -I I . ACENAPHTHENEQUINONE A. Introduction Study of the c r y s t a l structure of acenaphthenequinone-was undertaken as part of an investigation of a series of acenaphthene derivatives. B. Experimental Crystals of acenaphthenequinone are orange-yellow needles elongated along the c-axis, with the (010) face we l l developed. The c e l l dimensions and apace group were determined from Weissenberg and precession photographs of a c r y s t a l mounted about the-c-axis. The density was measured by f l o t a t i o n i n aqueous potassium iodide. Crystal Data. Acenaphthenequinone, - C 1 0Hg(C0) 2; M=l82.2; m.p. 273-274°C. o 03 Orthorhombic, a=7.8l+0.01, b=27.0+0.05, c=3.851+0.005A. U=8l2A . D x(with Z=4) =1.49, 1^=1.48 gm.cm 7 Absorption c o e f f i c i e n t s for X-rays, ?v. =1 • 54l8°\., i 0 1 u=9-83 cmt ; 7v=0.7107A, u=1.24 cm 7 F(000)=376".'~ Absent spectra: hOO-when 4 h i s odd, OkO when ,k i s odd, 001 when t i s odd. Space group i s P2-]_2-]_2-L-D2 . For in t e n s i t y purposes the hkO reflexions were recorded on mult i p l e - f i l m Weissenberg photographs, using u n f i l t e r e d CuK^ radiation. The 0k£, data were collected on precession films with related time exposures, MoK^ radiation being used. The - i n t e n s i t i e s were estimated v i s u a l l y . The r e l a t i v e values of the structure amplitudes were-derived by applying the usual Lorentz and po l a r i z a t i o n factors, the absolute scale being established l a t e r by correlation-with the calculated structure factors. Absorption corrections were considered unnecessary since the c r y s t a l used had a mean diameter of 0.06 mm. 152 independent hkO reflexions were observed (excluding the 020 r e f l e x i o n , which was cut off by the beam trap), representing 54$ of the t o t a l number th e o r e t i c a l l y observable with CuKc* radiation. Only 33 0 k £ reflexions were - 67 -_ . W ///» Figure 20. Relation of the o r i g i n of space group P2]_2]_2]_ to the origins of i t s projections on the pmacoids (100), (010), and (001). The several origins are indicated by dots. After Buerger, Barney and Hahn(79)» Table VIII. Transformations between Space Group and Projection Coordinates. Space Group Projection Coordinates Coordinates (OOl) (100) (OlO) x x ' = x - £ x"=x x'"=x y y'=y y"=y-<: y"'=y - 68 -recorded, representing about 20$ of the t o t a l number observable. C Structure Analysis Space group • P2]_2l2]_ • i s non-centrosymmetric, but i t has centrosymmetric projections (plane group pgg) i n a l l three p r i n c i p a l projections (Figure 20). The relations between space group and projection coordinates are-those formulated i n Table VIII. [00l] Projection The shortness of the c-axis promised good resolution of a l l the atoms i n t h i s projection. Packing and symmetry considerations suggested that the four molecules i n the unit c e l l must be•lined up approximately i n the direction of the b-axis. The search for a t r i a l structure was guided by the observation that the OkO reflexions exhibit a d i s t i n c t i v e feature," being r e l a t i v e l y weak for k=4n+2 and strong f o r k=4n. The very strong 0 , 2 4 , 0 r e f l e x i o n corresponds to a planar spacing of 1.13ft, which i s s l i g h t l y less than half the-width of a benzene ring. This indicated that i n the c-axis projection the aromatic carbon atoms must l i e very close to the ( 0 , 2 4 , 0 ) planes. The angle between the molecular plane and the (OOl) plane was estimated to be about 2 4 ° by comparing the lengths of the molecule and the a-axis. (The f i n a l results show i t to be 29°)• The orientation of the aromatic nucleus was also i n complete agreement with that deduced from the "benzene" re f l e c t i o n s . The x and y parameters referred to the molecular o r i g i n (defined as centre of the Cc;a-C8b hond) were obtained from the projection of a CENCO Petersen molecular model held i n the deduced orientation. Examination of the Patterson projection along [OOl] (Figure 21) confirmed the above deductions. From the multiple vector peak between naphthalene rings related by symmetry, the coordinates of the molecular o r i g i n were estimated as y o =0.125, x o =0.190 or O.3IO. The former value f o r x Q was taken since i t gave - 69 -Figure 21. Patterson projection along [c-Ol]. Contours are drawn at arbitrary i n t e r v a l s . Diagram of one molecule i s superimposed. - 70 -better agreement between the observed and calculated structure amplitudes for some low-order reflexions. (The f i n a l coordinates of the molecular o r i g i n are x Q=0.1762, y o =0.12U9). Structure factors were now calculated for a l l hkO reflexions using the carbon and oxygen scattering factors from Tabellen,zur Rontgenstrukturanalyse (50), with an o v e r a l l isotropic temperature factor 1 ° 2 . o B=4.5A . The discrepancy factor R for the observed reflexions was 0.408, but there-appeared to be no serious discrepancy between the observed and calculated structure amplitudes. 123 terms (including F(000)) were used i n a Fourier synthesis, which gave good resolution of a l l the atoms^ Recalculation of the structure factors with atomic coordinates determined from the electron-density map reduced R to 0.288. Refinement of p o s i t i o n a l and"temperature parameters proceeded by computing successive (F 0-F c) syntheses, and after f i v e cycles R dropped to 0.150. At t h i s point, the contributions of the hydrogen atoms were considered. The p o s i t i o n a l parameters were obtained by measurement on a molecular model. An isotropic temperature factor of 5-°A^ was assigned to each of the six hydrogen atoms. The inclusion of these hydrogen-atom contributions led to a si g n i f i c a n t improvement i n the agreement of the low-order data, especially the OkO reflexions, and the R factor was lowered to 0.139-Measured and calculated structure factors are compared i n Table A-5, and the f i n a l hkO F Q synthesis i s shown i n Figure 22. ClOO] Projection Since the number of observed Ok-t reflexions was smaller than the number of parameters to be determined good resolution was not expected i n t h i s projection. Approximate z coordinates for the carbon and oxygen atoms were obtained by measurement on a molecular model. The i n i t i a l 0k£. discrepancy was 0.190 for the observed reflexions, and t h i s was reduced by an (F 0-F c) - 71 -0 1 2 3 A 1 1 1 1 1 1 1 ' 111 i i i I Figure 22. Electron-density projection along foOll. Contour l i n e s o-2 Q - 2 are drawn at intervals of 1 e.A starting with 1 e.A . - 73 -synthesis to 0.116. Hydrogen-atom contributions were not considered. Measured and calculated Okt structure factors are included in-Table A-5- The f i n a l electron density projection.along [[lOOjis shown i n Figure 23-Coordinates and Molecular Dimensions The f i n a l p o s i t i o n a l and i n d i v i d u a l temperature 'parameters are l i s t e d i n Table IX where the atomic coordinates are referred to the space group o r i g i n and expressed as fractions of the u n i t - c e l l edges. The coordinates of the carbon and oxygen atoms can be f i t t e d to the equation 0.3284X + O.35U8Y - O.875UZ - 2.3951 = 0 o where X,Y,Z are coordinates expressed i n Angstrom units. The deviations of the-atoms from t h i s plane are l i s t e d i n the l a s t column of Table IX. The bond 1lengths and valency angles, calculated "from the x,y,z coordinates of Table IX, are shown i n Table X. There are no s i g n i f i c a n t differences between chemically equivalent bonds, and the average dimensions of the molecule, assuming Cg symmetry, are shown i n Figure 2k. The orientation of the molecule i n the unit c e l l i s given i n Table XI i n terms of the angles 7 6 ^ f L, <*>L ; T^M, V% W M ; 8 1 1 ( 1 ^N, V% °°N which the molecular axes L, M (see Figure 2k) and the plane normal K make with the crystallographic axes. The axis L was"taken through the mid-points of the C3-C1+ and Cy-Cg bonds, and axis M through atom C^a and the centre of the C 1 - C 2 bond. L, M and N are thus not exactly orthogonal, the angles being ^ LM = 88. 5 ° , M^W = 9 0 . 9 ° , and -^LW = 8 9 . 9 ° . The angle between the plane of the molecule and the (OOl) plane i s 2 8 . 9 ° . - 7k -Table IX. F i n a l Parameters* Atom X y z ,o2. B(A ) (X) C l 0.7542 0.1556 0.296 5-2 +0.032 c 2 O.7852 0.1025 0.170 5-2 +0.028 c 2 a O.6267 0.0864 -0.005 4-3 +0.057 C 3 0.5745 0.0427 -0.143 4.1 -0.030 ck 0.4006 0.0407 -0.276 4-9 -0.047 c 5 0.2910 0.0802 -0.262 4-5 +0.003 C 5 a 0.3437 0.1242 -0.109 4.1 +0.044 C6 0.2390 0.1659 -0.062 4-5 +0.016 CT 0 . 3 0 4 8 0.2052 0.118 4.9 -0.045 C8 0.4779 0.2097 0.253 4.1 -0.013 c 8 a 0-5757 O.1683 0.201 4-3 +0.016 c 8 b O.5086 0.1256 O.O37 • 3.6 -0.012 Cl 0.8533 0.1793 0.457 5-7 -0.029 °2 O.9168 O.O805 0.223 •5-7 -0.024 H 3 O.658 0.013 5.0 H 4 O.364 0.006 5-0 H 5 0 . l 6 l O.O73 5-0 H 6 0.111 O.163 5.0 H ? ,0.237 0.236 5.0 H 8 0.517 0.240 5.0 * Subscripts of the oxygen,and hydrogen atoms indicate the-carbon atoms to which they are attached. - 75 -Table X. Bond Lengths and Valency Angles Atoms Bond Lengths Atoms Bond Lengths 1-2 1-533 A 5-5a 1.389 ft 2-2a 1.473 5a-6 1.403 2a-8b 1.413 6-7 1.368 8b-8a 1.415 7-8 1.452 8 a - l 1.482 8-8a 1.369 2a-3 .1-357 8b-5a 1.406 3-4 1.474 1-Oi 1.180 4-5 1.369 2 - 0 2 1.204 Atoms Valency Angles > Atoms Valency Angles l - 2 - 2 a 106.9° 8a-8b-5a 1 2 2 . 7 ° 2-2a-8b 105-5 8b-5a-6 117.4 2a-8b-8a 115-2 5a-6- 7 118.0 8 b - 8 a-l 105.7 6-7- 8 125.8 8 a - l - 2 106.7 7-8- 8a 114.2 2 a - 3 - 4 117.2 8-8a-8b 121.6 3-4- 5 122.9 1-2 - 0 2 122.9 4 - 5 - 5a 119-8 2a-2 - 0 2 I3O.3 5-5a-8b 117.6 2-1- 01 124.7 5a-8b-2a 121.6 8 a - l - 0± 128.4 8b-2a-3 120.0 F i g u r e 2h. "Numbering and average dimensions of the m o l e c u l e . - 77 -Table XI. Molecular Orientation i n the Crystal 8 1 . 0 ° 2 1 . 7 ° 109.2° 1 5 9 - 3 ° V-VL = 89-8° V'N = 1 1 0 . 8 ° co L = 108.5° ^M = 68.4° = 2 8 . 9 0 Standard Deviations The standard deviations for the x and y coordinates, calculated from the hkO data using Cruickshank's formulae, are C r(x).= CX^y)^ 0.015°v f o r carbon, 0.011A f o r oxygen. CT(z) was not calculated from the 0k£ structure factors, which are few i n number, but i s c e r t a i n l y somewhat greater. The standard deviation of the bond lengths are about 0.02ift for C'-C bonds and 0.01c;ft for c=0 bonds. These values may be compared with the root mean square deviation o of the ind i v i d u a l bond lengths from the mean distances, which i s only 0 .007A. A l l valency angles have a standard deviation of approximately 1 . 3 ° . Intermolecular Distances A l l the intermolecular distances correspond to normal van der Waals interactions. The perpendicular distance between molecules related by tra n s l a t i o n c i s 3-37ft- Packing of the molecule and some shorter l a t e r a l intermolecular contacts are i l l u s t r a t e d i n Figure 25-D. Discussion The acenaphthenequinone molecule i s probably planar within the l i m i t s of experimental error. The maximum deviation from the mean molecular plane i s 0.057ft f o r carbon atom Cga* but t h i s and another apparently large deviations from pl a n a r i t y are due to the fact that the z coordinates have been determined somewhat imprecisely. Since the c-axis i s only 3-851ft long, s l i g h t errors i n z w i l l not however have a s i g n i f i c a n t effect on the measured bond lengths and valency angles. - 7 8 -0 1 2 3 4 5 A 1 I I I I 1 Figure 25* Projection of the structure along [ 0 0 l ] , showing the shorter intermolecular contacts. - 79 -I t i s interesting to compare the dimensions of the acenaphthenequinone molecule (Figure 24) found i n the present work with those of naphthalene, acenaphthene, 5>6-dichloroacenaphthene, and pyracene (Figure 19). The va r i a t i o n of bond lengths i n the aromatic nucleus i s very similar i n a l l four molecules. Fusion of one (or two) five-membered ring(s) to the system causes d i s t o r t i o n of the valency angles, which i s shared out by the entire molecule. The apex Cga-C8-b-C2a angle of the p e r i - r i n g has a mean value of 1 1 4 ° , which i s just midway between the i n t e r i o r angles, 108° and 120° respectively, of a regular pentagon and a regular hexagon. In acenaphthenequinone the a l i p h a t i c C^-C^ bond has a length of 1. 53+P-02^, which agrees well with the value reported for acenaphthene; the angles i n the p e r i - r i n g are also similar. The length of the 02~^2B. bond i s 1.48ft ( CT = O.Oli+ft). On the basis of the standard deviation, t h i s bond shrinking i s possibly s i g n i f i c a n t and would seem to indicate some conjugation between the aromatic nucleus and the carbonyl groups. Shortening of bonds i n a strained system -as a result of conjugation has been observed previously. In cis-l,2-dichlorobenzocyclobutene, f o r example, a mean length of 1.452. has been reported f o r the peri-bonds (80). The C=0 distance of I.19X i s quite similar to the length: found i n p-benzoquinone ( 8 l ) and most ketones ( 5 l ) . The C=0 bonds make exterior angles of 124° and 129° with the p e r i - r i n g ; t h e i r orientations are such that the intramolecular distances 02-• • and 0 2 . . . . C 2 a have the same length (2.41ft), and the O 1 . . . . O 2 distance i s 2. 86ft. - 80 -I I I . cis-1,2-ACENAPHTHENEDIOL A. Introduction For cis -1 ,2-acenaphthenediol molecular models show that the oxygen-oxygen distance i s less than the normal van der Waals separation. There i s some evidence that an in t e r n a l hydrogen "bond exists between the eclipsed OH groups. Study of the infrared spectrum of cis -1,2-acenaphthenediol i n d i l u t e carbon tetrachloride solution by Moriconi and co-workers (82) revealed two absorption bands for bonded hydroxyl groups: a well-resolved peak at l) = 3584 cm 7 and a broad shoulder at l) = 35^3 c m ~ Moriconi et_ a l assigned the higher frequency to a weak OH. . . . TT interaction and the lower frequency to stronger i n t r a -molecular hydrogen bonding between vie-OH groups. S i m i l a r l y , Csizmadia and Hayward(64) examined the infrared spectrum of the c r y s t a l l i n e s o l i d and found two OH absorption bands of approximately equal i n t e n s i t y : the lower frequency at 3190 cm7"^ indicating intramolecular hydrogen bonding of considerable strength, in agreement with the assignment of Moriconi et_ a l , and the higher frequency at 3333 crn-"^ : being ascribed, more appropriately i n t h i s case, to intermolecular hydrogen bonding. Simple considerations of molecular geometry, however, suggest that the hydrogen bond between OH groups on adjacent carbon atoms, i f formed at a l l , can at most be a weak one. For the five-membered intramolecular chelate ring H C C the angle ft between the 0-H bond and the 0 . . . . 0 l i n e i s 35-40° i f standard values (-^O-C-C — 1 1 2 ° , ^ C-O-H =± 1 0 7 ° , 0 - H ^ 1 . 0 A , 0 0 — 2-7A) are assumed - 81 -for the "bond distances and valency angles, leading to a "contour" hydrogen "bond length of at least 3°^ The formation of a banana-type intramolecular hydrogen bond between the oxygen atoms would seem to contradict the generally accepted view that fi i s not greater than about 1 5 ° ( 8 3 ) . On the other hand,,if the proton were actually close to the-internuclear 0 . . . . 0 l i n e , a large s t r a i n energy would be expected for the excessive deformation of the C-O-H .bond angle. These arguments strongly suggest,that chelation i s rather u n l i k e l y , especially i n a c r y s t a l which affords ample opportunities for intermolecular hydrogen-bond formation. To test t h i s hypothesis and to obtain further structural data for the acenaphthene nucleus, the c r y s t a l structure of cis -1 ,2-acenaphthenediol was determined. i - 82 -B. Experimental A sample of cis -1 ,2-acenaphthenediol consisted of colourless needles elongated along the b-axis, with the (OOl) face-well developed. A l l the crys t a l s examined were twinned on (100). The density was measured by f l o t a t i o n i n aqueous potassium iodide. The u n i t - c e l l dimensions and space group were determined from rotation and o s c i l l a t i o n photographs of a c r y s t a l mounted about the b-axis, hot and hit Weissenberg fi l m s , and hkO and Okt precession •films. Crystal Data, cis-1,2-Acenaphthenediol, C12H10O2; M=l86.2; m.p. 218-219-5°C. Monoclinic, a=12.77+0.02, b=4.8U5+O.003, c=15-74+0.02A, p=lll°50'+5'. U=90U.O^. D x(with Z=U)=1.368, Dm=1.35g.cm"? Absorption c o e f f i c i e n t for X-rays, ^=1.5^l8°v, u=8.93cm~7 F(000)=392. Absent spectra: hOl when £ i s odd, OkO when k i s odd. Space group i s P 2 ^ c - • For the c o l l e c t i o n of inte n s i t y data a needle c r y s t a l of cross-section O.O9XO.O6 mm. was mounted about the b-axis. The i n t e n s i t i e s of the h0£ and hit reflexions were recorded on Weissenberg photographs, using CuK^ radiation, and multiple-films to correlate strong and weak reflexions. The ranges of hOt and hit i n t e n s i t i e s were about 7^60 to 1 and 18U00 to 1 respectively, . the estimates being made v i s u a l l y . Twinning of the c r y s t a l resulted i n the appearance of,two sets of reflexions on a Weissenberg f i l m (different c* axis) with occasional overlap. Fortunately one component of the twin was appreciably bigger than the-other (intensity r a t i o 8 to 3)* so that the spots from the two components could be distinguished, although often with some d i f f i c u l t y . No absorption corrections were considered necessary. The structure amplitudes were derived by the usual formulae,.the absolute scale being established- l a t e r by c o r r e l a t i o n with the calculated structure factors. I38 independent hOt reflexions and 2^6 hit reflexions were observed, representing 56$ and 1+9$ respectively of the possible number observable under the experimental conditions.. - 83 -C Structure-Analysis [OlO] Projection Since the b-axis i s reasonably short a good view of the molecule i s expected i n t h i s projection. The orientation of the aromatic nucleus was deduced f i r s t from the weighted reciprocal l a t t i c e and confirmed l a t e r from examination of the Patterson projection along the b-axis (Figure 26). The well-resolved intramolecular 0-0 vector peak indicated that the projection of the molecular axis M.(see Figure 28) must be almost p a r a l l e l to the a-axis. The highest peak on the Patterson map corresponded to the interaction between naphthalene rings related by symmetry and led to the coordinates XQ=0.207, ZQ=0.276 for the molecular o r i g i n , defined as the centre of the C^-Cg^ bond. (The f i n a l coordinates of the molecular o r i g i n are XQ=0.2008, ZQ=0.276I). The x and z parameters were then obtained from the projection of a CENCO Petersen molecular model held i n the deduced orientation. Structure amplitudes for the h0£, reflexions were calculated using the carbon and oxygen scattering factors from Tabellen zur Rontgenstrukturanalyse (50) and an ov e r a l l isotropic , o temperature factor B=4-5A. The discrepancy factor for 193 reflexions, including 55 unobserved reflexions with i n t e n s i t i e s taken at half the minimum observable l i m i t , was somewhat high (R=0.517)* However, there were no serious disagreements between the observed and unobserved structure amplitudes and th e i r calculated values. I t was possible to allocate signs to 9^ observed reflexions for a Fourier synthesis, and the res u l t i n g map-showed good resolution of a l l the atoms. Recalculation of the h0£ structure factors with the x and z coordinates of the electron-density maxima lowered R (observed reflexions only) to O.344. Refinement of the atomic parameters was carried out by means of successive (F 0-F c) syntheses, and after s i x cycles R was 0.148. The f i n a l difference map had a number of electron density maxima which could be attributed to the presence of hydrogen atoms. Although the electron F i g u r e 26. P a t t e r s o n p r o j e c t i o n a long [oio]. Contours are drawn at a r b i t r a r y i n t e r v a l s . A diagram of two molecules i s superimposed. --85 -density was negative.in the region between oxygen atoms i n the same molecule and p o s i t i v e i n the proximity of the intermolecular 0....G l i n e s , t h i s should not be taken as de f i n i t e evidence against i n t e r n a l hydrogen bonding since hydrogen atoms i n 0-H....0 bonds are d i f f i c u l t to locate by X-ray methods. Since the locations of the hydroxyl hydrogens were uncertain, p o s i t i o n a l parameters were deduced only for the eight hydrogen atoms attached to the carbon skeleton. When these hydrogen atoms were included i n the structure factor c a l c u l a t i o n , R was lowered to 0.131. The measured and calculated hO-6 structure factors are l i s t e d i n Table A-6,.and the f i n a l electron-density projection on (010) ,is shown i n Figure 27-y Parameters and F i n a l Refinement As good resolution of the i n d i v i d u a l atoms could not be expected i n the [lOO] and [OOI] projections, the y coordinates were deduced from the h i t data. Approximate y parameters referred to the molecular o r i g i n were derived from a molecular model, and the y-coordinate of the molecular o r i g i n was then varied u n t i l reasonable•agreement was obtained between the calculated and observed structure factors for a few low-order h i t reflexions. Structure factors were calculated for a l l the h i t reflexions, using the y coordinates thus determined and the x,z and B parameters from the h O t refinement. R was 0.2^2. For further refinement i t would be advantageous to use the complete three-dimensional data. However, indexing of the h2t and h3£ layers was d i f f i c u l t as a result of the twinning, and i n any case the proportion of observable reflexions on these upper levels became increasingly smaller. Since the observed h0£- and hl-E, reflexions constituted a large part of the observable three-dimensional data, refinement was completed by computing cosine and sine difference generalised projections, using the hl£ data and \ - 87 -r e f i n i n g a l l the x,y,z and B parameters simultaneously. 'After s i x cycles R was 0.173 for "the observed h i t reflexions. The inclusion of the contributions from the eight hydrogen atoms previously considered led to a s i g n i f i c a n t improvement i n the agreement of the observed and calculated structure amplitudes, and R was lowered to 0.155- Measured and calculated h i t , structure factors are l i s t e d i n Table A-7-Molecular Dimensions and Orientation The f i n a l p o s i t i o n a l and temperature parameters are l i s t e d i n Table XII, where the atomic coordinates, are expressed as fractions of the u n i t - c e l l edges, and x,z and B are the mean of h o t and h i t values. The equation of the mean plane f o r the carbon atoms i s o .7039X '+o .7i07Y+o .oi52Z'-2.5902=0 , where X',Y and Z' are coordinates expressed i n % and referred to orthogonal axes a, b and c'. The deviations of the atoms from t h i s plane a r e . l i s t e d i n the l a s t column of Table XII. The dimensions of the molecule, calculated from the atomic coordinates of Table XII, are given i n Table XIII. Since -differences between chemically equivalent bonds are of doubtful significance, mean values for the bond distances and valency angles were obtained by assuming symmetry C s for the molecule (Figure 28). , The orientation of the molecule i n the unit c e l l i s given i n Table XIV i n terms of the angles -/^ W L. 7 ^ fM> <*>M. ^ cO N which the molecular axis L, M (see Figure 28), and the plane normal N make with the orthogonal system a, b and c 1. The axis L was taken through the centres of the C^ -C^ , and C^-Cg bonds, and axis M through atom C^a and the mid-point of the C]_-C2 bond. L, M and N are thus not exactly perpendicular to one another, the angles being ^-LM=90.40, ^-MN=89-8Q, and ^ LN=90.0 G. - 88 -Table XII. F i n a l Parameters* Atom X y z B ( f ) C l 0.3922 0.101+ 0.3255 l+.l +0.021+ c 2 0.3366 0.110 0.2161+ 1+.6 -0.029 c 2 a 0.21+81+ 0.320 O.193I ^•5 -0.008 C 3 0.1718 0.1+37 0.1113 5-3 +0.025 ck O.O9U8 0.6kQ 0.1173 1+.8 +0.036 c 5 O.O887 0.737 O.I9I+7 k.k -0.011+ C 5 a , 0 . l 6 l 9 0.61+0 O.2789 l+.l; -0.018 C6 O.1687 0.720 O.3705 •k.k -0.038 c 7 0.21+90 0.619 0.1+1+22 5-^ +0.057 C8 0.3291 0.391 0-1+393 5-5 +0.002 C8a 0.3228 0.309 0.3522 l+.l +0.003 c 8 b 0.2396 0.1+23 0.2733 l+.l -0.01+1+ Ol 0.5109 0.167 0.3596 1+.6 +1-175 °2 0.1+182 0.170 0.17I+2 k.k +I.075 % O.386 -0.100 0-351 6.0 H 2 0.305 -0.083 0.191 6.0 H 3 O.179 0.329 0.053 6.0 ?1+ ,0.01+0 0.750 0.055 6.0 H 5 0.027 0.889 0.202 6.0 H6 0.110 •0.871+ 0-377 6.0 H ? 0.721 O.505 6.0 H8 0.399 0.289 0.1+93 6.0 * Subscripts of the oxygen and hydrogen atoms indicate the carbon atoms to which they are bonded. - 89 -Table X I I I . Bond Lengths, Valency Angles and Some Intramolecular Approach Distances Atoms Bond Lengths Atoms Bond Lengths 1-2 1.596ft 5-5a .1.389ft 2-2a 1.1+61 5a-6 1.1+61+ 2a-8b 1.1+00 6-7 1.306 8b-8a 1.1+13 7-8 1.519 8a-l 1-^93 ,8-8a 1.1+01 2a-3 l.klk 8b-5a 1.1+71 3-h 1.1+1+6 1-0! 1.1+58 h-=122°12'+5'. U=1177.3^3. D x(with Z=4)=1.557> D m=l-53 gm.cmT3 Absorption c o e f f i c i e n t s for X-rays, "X =1. 5U18A, |u=12.70 cm!"1 ; ?v. =0. 7IO7A, /u=1.57 cmT 1 F(000)=568. Absent spectra: hOt when tis odd, OkO when k i s odd. Space group i s P2 1/ c-c| h. For the c o l l e c t i o n of i n t e n s i t y data a needle c r y s t a l of cross-section 0.07x0.11 mm. was mounted about the b-axis. Equi-inclination Weissenberg photographs of the hOt and hit layers were taken with CuK^ radiation. To extend the i n t e n s i t y range the data f o r each zone were collected on two sets of four films related by time exposures. The i n t e n s i t i e s of the various reflexions were estimated v i s u a l l y and corrected as usual for Lorentz and p o l a r i z a t i o n factors. Wo absorption corrections were considered necessary. 246 hOt (excluding the 100 and 102 reflexions which were cut off by the beam trap) and 443 bit1- independent reflexions were found to be of measurable magnitude; these represent 75$ and 76$, respectively,,of the t o t a l number th e o r e t i c a l l y observable. C Structure Analysis The f i r s t attempts to derive an approximate structure made use of the set of h0£ data. A Patterson synthesis projected down the short b-axis (Figure 3l),was computed. The highest peaks on t h i s map were readily i d e n t i f i e d as multiple vector peaks between naphthalene rings related by symmetry, leading to a p o s i t i o n of x Q =0.258, zQ=0.196 or xo=0.242,. z o=0.304 for the molecular o r i g i n , defined as the centre of the 0^a-CQ^ bond. The orientation of the aromatic nucleus indicated by the Patterson map was i n agreement with that deduced from an examination of the weighted reciprocal l a t t i c e . The extended peak marked with a cross (about 3.4°v from the origin) - 99 -c o u l d b e r e a s o n a b l y a s c r i b e d t o < i n t e r a c t i o n s b e t w e e n n o n - b o n d e d n i t r o x y g r o u p s . On t h i s b a s i s s t r u c t u r e ( X X I l ) , w i t h i t s many c o n f o r m a t i o n s i n v o l v i n g r o t a t i o n s a b o u t C-0 a n d 0-N s i n g l e b o n d s , , w a s t a k e n a s a s t a r t i n g p o i n t f o r t h e p r e c i s e l o c a t i o n o f atoms b y F o u r i e r m e t h o d s . [OlO] P r o j e c t i o n The s h o r t n e s s o f t h e b - a x i s p r o m i s e d a g o o d v i e w o f t h e s t r u c t u r e i n t h i s p r o j e c t i o n . The x a n d z c o o r d i n a t e s o f t h e c a r b o n atoms w e r e o b t a i n e d f r o m t h e p r o j e c t i o n o f a CENCO P e t e r s e n m o l e c u l a r m o d e l ' ( F i g u r e 36) h e l d i n t h e d e d u c e d o r i e n t a t i o n , t h e m o l e c u l a r o r i g i n b e i n g a r b i t r a r i l y p l a c e d a t x o =0.258, z Q =0.196. V a r i o u s s e t s o f x a n d z p a r a m e t e r s w e r e p o s t u l a t e d f o r t h e o x y g e n a n d n i t r o g e n a t o m s , a l l o w i n g f o r t h e f a c t t h a t t h e two n i t r o x y g r o u p s must be . O M M a p p r o x i m a t e l y 3 -^A a p a r t , a n d o r i e n t e d i n s u c h a w a y , t h a t t h e ' t h i c k n e s s o f t h e m o l e c u l e i n t h e [OlO] d i r e c t i o n was n o t e x c e s s i v e . The d i f f e r e n t t r i a l s t r u c t u r e s w e r e t e s t e d b y c a l c u l a t i n g hO-t s t r u c t u r e a m p l i t u d e s a n d c o m p a r i n g t h e m w i t h t h e o b s e r v e d v a l u e s . The a t o m i c s c a t t e r i n g f a c t o r s were t a k e n f r o m t h e I n t e r n a t i o n a l T a b l e s , V o l . I l l , a n d a n o v e r a l l i s o t r o p i c t e m p e r a t u r e f a c t o r B=U.5?L2 was u s e d . F i n a l l y a s t r u c t u r e w h i c h gave r e a s o n a b l e a g r e e m e n t w i t h t h e l o w - o r d e r r e f l e x i o n s was c h o s e n f o r r e f i n e m e n t . The d i s c r e p a n c y f a c t o r R ( o b s e r v e d r e f l e x i o n s o n l y ) was 0 . 6 l 8 , a r a t h e r h i g h v a l u e , b u t i t was p o s s i b l e t o a l l o c a t e s i g n s t o 155 o b s e r v e d r e f l e x i o n s f o r a F o u r i e r s y n t h e s i s . A l l t h e a toms c o u l d b e i d e n t i f i e d , a n d t h e r e were no s p u r i o u s d e t a i l s i n t h e e l e c t r o n -d e n s i t y map. H o w e v e r , f u r t h e r r e f i n e m e n t p r o v e d l e s s e n c o u r a g i n g a n d R c o u l d n o t b e i m p r o v e d b e l o w a b o u t O.UO. T h i s s u g g e s t e d t h a t t h e m o l e c u l e h a d e s s e n t i a l l y t h e c o r r e c t s t r u c t u r e a n d o r i e n t a t i o n , b u t was w r o n g l y p l a c e d i n t h e u n i t c e l l . New x a n d z c o o r d i n a t e s f o r a l l t h e atoms were now d e d u c e d w i t h t h e m o l e c u l a r o r i g i n s h i f t e d t o t h e a l t e r n a t i v e p o s i t i o n xQ=0.2k2, z o =0.304. R e c a l c u l a t i o n o f t h e hOE. s t r u c t u r e f a c t o r s gave a n R v a l u e o f O.523 a n d i n Figure 32. Electron-density projection along [oio] . Contour l i n e s are drawn at intervals of 1 e.A - 2 s t a r t i n g with 1 e . i . - 101 -f i v e cycles of refinement by- difference synthesis, t h i s was reduced to 0 . l 6 0 . The f i n a l electron-density projection on ( 0 1 0),is shown i n Figure 32-y Parameters, and F i n a l Refinement To"determine the y coordinates of the atoms,, attention was turned,to the h i t data. Approximate y, parameters referred to the molecular o r i g i n were derived from a molecular model (Figure 36), and the y, coordinate of the molecular o r i g i n was chosen as that which gave the best agreement between the calculated and observed structure-amplitudes for a few low order data. Structure factors were now calculated for a l l hlE* reflexions,, using the y coordinates thus determined and the x, z ,and B parameters from the h O t refinement. The i n i t i a l value of R for the observed reflexions was 0.3^7-Refinement of a l l the p o s i t i o n a l and temperature parameters proceeded by computing cosine and sine difference generalized projections, and after f i v e cycles R dropped to 0.169- The observed values for the very intense 211, 312, 212, 313,.and 213 reflexions were considerably•larger than F , probably due to errors,in i n t e n s i t y estimation, and these planes were omitted i n evaluating R. Structure factors were again calculated for the h O t reflexions with the parameters determined from the hl£. refinement; the R value was reduced s l i g h t l y from 0.160 to 0.1^5. Measured and calculated h O t 1 and h i t structure factors a r e ' l i s t e d i n Tables A-8 and A-9 respectively. Coordinates, Molecular Dimensions, and Orientations The f i n a l p o s i t i o n a l and temperature parameters are given i n Table XV, where the atomic coordinates are expressed as fractions of the unit-cell-edges. The dimensions of the molecule, calculated from these coordinates, are shown i n Table XVI. Mean bond lengths and valency angles were obtained by assuming symmetry C s for the cis -1 ,2-acenaphthenediol portion of the molecule (Figure 33)* - 102 -Atom X Table-XV. y F i n a l Parameters ,' z .02. B(A ) A (A) C l 0.323^ 0.1+55 O.2289 U-3 -0.003 C 2 O.2187 O.387 O.I56I+ k>3 +0.038 C 2 a O.17I+6 0.193 O.19I+I 1+.1+ -0.031+ C 3 O.0871 0.080 0.1617 5.0 <+0.008 ch O.0681 - 0 . 0 8 l 0.2181 5.8 -0.002 c 5 0.1336 -0.116 0.3015 5-6 -0.023 O.2230 0.021+ O.33I+I 5-2 +0.020 C6 O.29I+3 0.008 O.I+I72 +0.019 c 7 0.3780 0.11+0 o . U U o o h.9 -+0.005 C8 0.3982 O.306 0.3852 +0.035 C 8 a 0.3268 0.298 0.3019 -0.053 C8b 0.21+09 0.171 0:2786 1+.8 -0.006 ° 1 0.3882 0.273 0.2168 1+.6 +0.007 N 0.1+070 0.398 0.1592 h.9 -0.030 02 0.3660 O .63I 0.1230 6.1 •+0.010 °3 0.1+675 0.262 0 .1605 5-7 +0.011 ° i 0.2216 0.191 0.091+7 5.0 -0.015 N " 0.1530 0.257 0.0120 5-2 +0.058 °2 O.0915 0.1+21+ 0.0009 7.2 -0.025 °3 O.1636 0.082 -0.0333 6.8 -0.021 - 103 -Table XVI. Bond : Some : Lengths, Valency, Angles and Intramolecular Approach Distances Atoms Bond Lengths • Atoms Bond Lengths . /Atoms Bond Lengths 1-2 1.603ft k-5 1.388ft 1 - 0 ! 1.U67& 2-2a 1-533 5-5a I.436 0 i -N ,1.408 2a-8b •1.401 5a-6 1.401 N-0 2 1.196 8b-8a 1-396 6-7 1-373 N-O3 1-173 8 a - l I.523 7-8 1.451 2-0j_ 1.468 2a-3 1-365 8-8a 1.402 t 1 0 1 -N 1.410 1.455 8b-5a 1.401 N'-O2. t 1 N -O3 I.189 ,1.227 Atoms Valency Angles Atoms Valency'Angles Atoms Valency- Angles l - 2 - 2 a 106.9° 8b-2a-3 1 2 1 . 2 ° 1 t > •Oi-N - 0 2 , 1 1 6 . 5 ° 2-2a-8b 106.5 8a-8b-5a 123.2 t f 1 Oi-N -O3 109.2 2a-8b-8a 114.4 8b-5a-6 118.4 t i 1 0 2 -N - 0 3 133-1 8 b - 8 a-l 110.9 ,5a-6 -7 118.1 0±-l -2 110.9 8 a-l -2 101.3 6-7 -8 125.2 Oi-1 - 8 a 104.7 2a-3 -h 116.8 7-8 -8a 114-5 1 -Oi-N 115-7 3-k -5 123.O 8-8a-8b 120.2 Oi-N - 0 2 117-3 4-5 -5a 118.4 0 i - 2 -1 107.4 Oi-N -O3 •111.5 5-5a-8b 117.8 0[-2 -2a 108.2 0 2-N -O3 131.0 5a-8b-2a 122.6 2 -Oi-N 1 115-h continued on page 108 - 104 -F i g u r e 33. Numbering and average dimensions of the m o l e c u l e . - 105 -and by, averaging corresponding values for the two nitroxy groups (Figure 37)• The equations of the mean planes are Carbon atoms : -O.U699X' + O.8658Y + 0.1720Z' - O/813I+ = 0, Unprimed 0N0 2 : 0.3583X' + 0.5907Y' + O.7229Z' - U.8051 = 0, Primed 0N0 2 : 0.6638X' + O .7U5UY- 0 . 0 6 l 6 Z ' - 2-3966 = 0, where X', Y, Z' are coordinates expressed i n % and referred to orthogonal axes a, b and c T. The deviations of the atoms from these planes are l i s t e d i n the l a s t column of Table XV. The unprimed and primed 0N0 2 groups (Figure 35) are i n c l i n e d to the plane of carbon atoms at angles of +62.1° and + 7 1 - 2 ° respectively. The orientation of the molecule i n the unit c e l l may be indicated by giving the angles 9^> V 'and ^ (Table' XVIl), which the molecular axes L,M (Figure 33) and the carbon-plane normal N make with the a and b c r y s t a l axes, and t h e i r perpendicular c'. The axes L'was taken through the mid-points of bond C-^ -C^ and Cy-Cg, and axis M through C^a and the centre of the C]_-C2 bond. L, M, and N are thus not mutually orthogonal, the angles being /-LM=90.6°, ^LN=90.2°, and ^MN=90.0°. - 106 -Table XVII. Molecular Orientation i n the Crystal 128.9° ^ M = 51-5° T^N - 118.0° 101.4° ^ M = 6 2 . 5 0 y- H - 30.0° c o L - 138.7° M 129.1° <*>N = 8o. i ° Standard Deviations The standard deviations for the x and z coordinates, calculated using Cruickshank's formulae, are cT(x),= ( 7 ( Z ) , = 0.010ft for C, 0.00&A for ©i, 0.009ft for N, and 0.010ft for 02 and O3. tT(y) ,is expected to be somewhat greater. The standard deviations of the measured bond distances are about 0.0l4ft for C-C and N=0 bonds, 0.013ft f o r C-0 and 0.012 for 0-N .bonds. • A l l valency angles have a standard deviation,of approximately 0.9°-Intermolecular Distances A l l the intermolecular distances correspond to normal van der Waals interactions. Packing of the molecules i n the unit c e l l and some shorter l a t e r a l intermolecular contacts are shown i n Figure 3^ > D. Discussion The y coordinates have not been determined to a high degree of accuracy so that the apparent deviations from the mean planes of the•acenaphthene nucleus (maximum value 0.053 for 03 a ) and of the nitroxy groups (maximum value O.O58 f o r N') are probably not s i g n i f i c a n t . Since the b-axis i s short small errors i n the y parameters should not seriously affect the measured bond lengths and valency angles. The molecular structure of cis-1 ,2-acenaphthenediol d i n i t r a t e i s shown in perspective i n Figure 35- The nitroxy groups are w e l l separated from eac t o other, the two shortest contacts between them being O1-O1 =2-57A and 0]_-02 =2.9lft- The planes of the nitroxy groups are i n c l i n e d i n the same I—1 o Figure 3^, Projection of the str.uc.ture along ,[oio] - 108 -Figure 35. Perspective diagram of the molecular structure. Selected Intramolecular Approach Distances Atoms Distances Atoms Distances Atoms Distances 0 2-57A ° 1 " 2 0 2-53A 1-N , 0 2.1+3A 0J^-2a 2.^3 2 -W 2 A 3 i - o 2 2.61 2.1+8 2 -0> 2.60 ° i - ° 2 2.91 0 ]_-8a 2-37 Fig. 36. CENCO P&tersen m o l e c u l a r model photographed in two a r b i t r a r y d i r e c t i o n s to s h o w "its genera l Snape. - 110 -( b ) 0 3 (c) F i p u i - 37. Dimensions of the n i t r o x y group i n (a) cis-1,2-acenaphthenedio l d i n i t r a t e , (b) p e n t a e r y t h r i t o l t e t r a n i t r a t e , and (c) n i t r i c a c i d . - I l l -sense with respect to the plane of carbon atoms. Figure 36 shows a CENCO molecular model viewed i n two arbitrary directions. The dimensions of the acenaphthene nucleus of cis-1,'2-acenaphthenediol d i n i t r a t e are very similar to those found i n other acenaphthene derivatives. The lengths of bondB C2 a - C 3 , C^-Cip. C^-Ctj • vary i n the order short-long-short, as do'the corresponding distances i n naphthalene. o The a l i p h a t i c C1-C2 bond has a length of I.6O3+O.Ol^A (projection on (010) 1.57Q°Y), which agrees we l l with the value 1. 59g+0.Ol^X found i n cis -1 ,2-acenaphthenediol. The s i g n i f i c a n t lengthening of t h i s bond, as o o compared to the values l.^kk and 1-53-A found i n acenaphthene and acenaphthene-quinone respectively, may be ascribed to steri c repulsion of the non-bonded 1 oxygen atoms 0-j_ and 0-]_. The bond lengths and valency angles of the nitroxy group found i n the present study are compared with those of pentaerythritol t e t r a n i t r a t e (88) and n i t r i c acid (90) i n Figure 37- There i s excellent agreement among corresponding values, and i n both ni t r a t e s ^ -O^ NC^ i s s i g n i f i c a n t l y larger than ^0iN03 as a consequence of s t e r i c interference between atoms C and C^ -The appreciably larger temperature factor for atoms Cgand O3 than f o r N and Oi suggest to r s i o n a l o s c i l l a t i o n of the n i t r o group .about the 0-N bond, i n a manner sim i l a r to the motion observed i n U-nitroaniline (91)• I t ' i s also probable that the nitroxy group, as a whole, executes t o r s i o n a l o s c i l l a t i o n about the C-0 bond. These l i b r a t i o n a l movements are expected to cause an apparent diminution of the measured Ef=0 distance (92), and i t i s suggestive that the present measured value of 1.19^+0.00^2. i s s l i g h t l y smaller than the corresponding length (l.2 1 ^ + 0 . 0 l 2 ) ,in pentaerythritol t e t r a n i t r a t e for which thermal motion i s smaller. Since anisotropic thermal factors have not been determined i n the present analysis, no attempt has been made to correct the bond distances for ro t a t i o n a l o s c i l l a t i o n errors. - 112 -V. GENERAL CONCLUSIONS From a c r i t i c a l examination of the structural data of acenaphthene and i t s derivatives, the following conclusions may.be drawn: (a) .The carbon skeleton i s planar. (b) The s t r a i n , i n the p e r i - r i n g i s a l l e v i a t e d p r i n c i p a l l y by the di s t o r t i o n of bond.angles,. both i n the; p e r i - r i n g and i n the naphthalene rings. (c) In cis-1,2-disubstituted .acenaphthenes the C\-C2 bond i s s i g n i f i c a n t l y longer than the corresponding distance i n acenaphthene, probably as a consequence of steric repulsion between the non-bonded substituents. (d) In acenaphthenequinone the short peri-bonds C-j_-Cga and..C2"C2a suggest some degree of conjugation between.the carbonyl groups and the aromatic nucleus. The si g n i f i c a n t shrinking of these bonds i n cls-1,2-acenaphthenediol i s less w e l l understood. (e) The average dimensions of the naphthalene moiety of the acenaphthene system,. derived from the data for acenaphthene,. 5>6-dichloroacenaphthene- and the three compounds studied i n the present work,: are shown i n Figure - 3 8 ; t h e i r deviations from the corresponding values.in naphthalene•are also indicated. The standard.deviations of the mean bond distances-are :about .0 ^o O.OOoA for bond C^-Cg^ and 0.006A for other bonds,, and of the valency, angles about 0.4°. I t i s seen that formation ..of the p e r i - r i n g results primarily, i n compression of the C2a-Cgk bond, stretching of the 0 2 3-0^ bond,.. and widening of the 02a-Cg^-C^a angle. In general the bond distances are affected to a lesser extent than.are the valency angles. - 113 -F i g u r e 38. Average dimensions of the naphthalene moiety of the acenaphthene system. D e v i a t i o n s from the c o r r e s p o n d i n g v a l u e s i n naphthalene are shovm i n "brackets; f o r the Q bond d i s t a n c e s the d e v i a t i o n s are g i v e n i n 10 A. APPENDIX I STRUCTURE FACTOR TABLES - 115 -Table A-l. Biphenylene hkO h k £ 0 Zc(2) 0 2 97.8 +112,1 +111.0 4 9.4 + 11.2 + 9.7 6 42.9 + 54.7 + 50.6 8 4.2 - 1.7 - 0.3 10 14.0 + 14.8 + 17.2 12 18.9 + 17.2 + 19.9 3 1 45.0 + 53.8 + 55.5 2 116.7 +134.0 +134.6 3 89.1 + 95.5 + 96.1 4 21.7 - 26.9 - 22.1 5 24.7 + 20.6 + 20.4 6 <3.1 + 1.0 + 1.4 7 3.2 + 3.3 + 4.7 8 7.0 + 1.9 + 3.1 9 5.2 + 3.0 + 4.0 10 11.4 - 15*9 - 16.5 11 < 3.4 - 1.7 - 0,8 12 <3.0 + 1.8 + 2.6 13 8.6 + 4.9 + 6.6 6 0 46.8 - 53.2 - 49.5 1 48.6 - 48.1 - 47.1 2 2.1 + 6.6 + 8.9 3 3.1 0 + 1.0 4 <2.5 - 4.1 - 3.1 5 30.7 + 26.6 + 29.0 6 31.2 - 28.9 - 30.9 7 <3.3 - 1.2 - 0.3 8 3.6 - 4.1 - 4.0 9 <3.6 + 0.7 + 1.5 10 3.6 - 2.6 - 2.0 5 0 5.9 0 0 8 4.0 0 + 1.3 10 2.6 0 + 4.0 11 2.8 0 0 2 1 2,1 0 + 1.3 4 2.5 0 + 0.9 7 2.2 0 - 1.1 8 2.8 0 - 1.8 16 4.4 0 - 1.5 2 2 8.8 0 + 0.6 4 3.1 0 0 5 6.2 0 + 1.5 h k h = 3 n 6 11 10.4 - 6.9 - 7.5 12 <2.7 - 4.7 - 5.0 13 5.1 - 7.5 - 7.9 9 1 4.9 + 4.4 + 1.4 2 30.8 +36.9 +30.8 3 34.7 -28.9 -33.0 4 32.8 +25.4 +28.4 5 12.4 -12.8 -14.2 6 <3.3 0 + 1.3 7 6.2 - 5.3 - 6.6 8 15.6 -15.3 -14.2 9 < 3.7 - 0.7 - 1.9 10 9.7 - 5.9 - 6.0 11 <3.0 + 2.2 + 2.0 12 <2.3 - 0.7 - 0.8 12 0 30.4 -27.5 -30.1 1 <3.0 0 + 0.5 2 11.8 - 8.4 - 9.4 3 10.9 + 9.2 +11.2 4 14.0 +13.4 +13.7 5 8.8 + 7.9 + 8.9 6 19.4 +16.2 +17.1 7 4.5 - 4.7 - 3.8 8 6.4 + 5.4 + 5.3 9 6,9 - 3.5 - 3.8 10 6.5 - 2.9 -. 4.8 11 3.0 - 2.9 - 2.6 12 <-1.4 - 0.1 - 0.5 15 1 <3.5 - 3.0 - 0.6 2 3.5 - 2.5 - 2.3 h / 3 2 10 2 4.4 0 - 0.3 11 4.1 0 + 3.0 16 5.2 0 + 1.1 2 3 10.6 0 - 0.7 4 2.1 0 - 1.3 5 6.2 0 + 1.7 7 3.5 0 .+ 1.4 8 6.3 0 + 1.1 10 3.6 0 - 2.1 13 3.4 0 + 1.4 17 5.3 0 - 1.5 4 4 1.6 0 - 1.2 h k lo IcCD P c(2) 15 3 21.9 -19.1 -18.4 4 5.2 - 6.7 - 6.1 5 3.7 + 2.6 + 3*7 6 <3.7 + 3.1 + 3.0 7 6.2 + 4.1 + 5.4 8 9.5 + 4.8 + 5.7 9 <3.0 0 + 0.8 10 < 2.4 - 2.1 - 2.2 11 <1.4 + 2.7 + 3.2 18 0 30.2 -28.3 -29.6 1 11.7 +11.4 +12.5 2 14.0 -11.3 -11.4 3 <3.7 + 2.8 + 3.3 4 5.8 - 6.9 - 6.0 5 7.1 - 6.0 - 7.1 6 10.5 -10.0 -10.2 7 < 3.0 + 1.1 + 1.1 8 <2.6 + 0.5 + 0.6 9 <2.0 - 1.8 - 2.2 21 1 19.8 -13.5 -16.9 2 16.8 -11.7 -14.0 3 5.5 - 2.6 - 4.0 4 <3.0 + 2.7 + 2.6 5 <2.8 - 2.8 - 4.5 6 7.2 - 1.0 - 0.9 7 <2.0 - 2.2 - 3.3 24 0 10.4 + 9.6 + 9.5 1 2.9 - 1.4 - 1.6 2 3.7 - 1.1 - 2.7 3 6.2 - 2.8 - 3.1 5 4 6.9 0 + 0.8 7 4.6 0 + 0.1 8 3.4 0 - 0.5 5 5 6.7 0 - 1.6 7 2.1 0 + 0,6 8 5.3 0 + 1.7 16 2.7 0 + 0.8 1 6 7.0 0 - 0.8 5 5.7 0 - 0.6 7 6.0 0 - 1.3 10 8 3*8 0 - 0.9 11 5.3 0 - 0.3 116 -Table A-2. Biphenylene hkl h k lo lc -20 0 4.2 - 4.2 -18 16.6 - 11.4 -16 12.2 - 12.6 -14 <4.0 + 0.7 -12 3.6 + 6.0 -10 <3.2 + 2.8 - 8 <2.7 + 2.0 27.6 + 29.6 - 4 16.7 + 24.1 - 2 Not obs. 0 Not obs. 2 Not obs. 4 16.0 + 21,7 6 29.8 - 37.5 8 <2.8 + 3.8 10 4.5 + 6.5 12 5.1 + 4.1 14 11.4 - 8.2 16 9.7 - 7.7 18 30.4 + 23.1 20 6.0 - 8.1 -22 1 8.9 - 7.2 -21 <4.0 + 6.5 -20 <4.2 - 3.6 -19 10.7 - 8.2 -18 4.4 + 1.4 -17 6.3 - 9.5 -16 <4.3 + 5.4 -15 4.2 + 4.7 -14 <4.0 + 1.3 -13 26.5 - 19.8 -12 22.9 - 22.0 -11 4.8 - 7.3 -10 7.8 + 5.2 - 9 20.6 - 18.7 - 8 18.6 + 7.4 - 7 18.2 + 13.9 - 6 21.5 +. 14.1 - 5 5.6 + 8.4 - 4 50.2 + 50.9 - 3 109.9 -101.2 - 2 18.2 +. 26.8 - 1 Not obs. 0 Not obs. 1 Not obs. 2 61.4 + 60.4 3 70.2 + 72.1 4 25.1 + 34.3 h k lc 5 1 26.0 + 25.4 6 16.9 - 12.1 7 2.6 + 3.5 8 <2.8 + 3.1 9 20.6 + 19.4 10 <3.2 + 1.8 11 10.8 - 13.6 12 25.0 + 25.2 13 10.9 - 11.3 14 4.0 + 3.2 15 4.2 + 3.5 16 <4.4 + 0.3 17 15.3 - 15.4 18 <4.4 - 4.7 19 <4.4 - 3.2 20 5.1 - 5.4 21 5.6 - 4.9 -18 2 4.4 - 4.7 -17 6.3 + 6.5 -16 12.4 - 13.8 -15 7.4 + 10.1 -14 13.0 - 11.4 -13 3.9 + 7.9 -12 3.7 + 4.7 -11 5.0 - 4.3 -10 8.1 - 12.3 - 9 26.8 + 23.2 -8 <2.9 + 2.3 - 7 10.1 - 4.8 - 6 47.5 - 45.6 - 5 4.7 + 0.6 - 4 80.6 + 83.8 - 3 74.9 - 74.4 - 2 <1.9 - 0,8 - 1 33.0 + 30.2 0 4.3 + 3.1 1 5.7 + 8,0 2 9.6 + 14.7 3 26.2 + 36.6 4 44.1 + 49.5 5 22.9 + 20.7 6 23.2 + 21.4 7 3.9 - 6.2 8 8.3 + 4.3 9 25.1 - 29.4 10 7.0 - 9.4 11 <3.5 - 1.8 12 3.7 + 4.8 h k lo lc 13 2 7.9 + 7.5. 14 21.0 - 21.4 15 13.5 - 15.7 16 9.8 - 5.9 17 <4.5 + 6.9 18 6.3 + 5.5 19 <4.3 - 1.1 20 <4.1 + 2.0 21 6.7 + 6.1 -19 3 4.3 + 5.7 -18 <4.4 + 3.4 -17 4.4 - 2.4 -16 <4.4 - 3.1 -15 11.4 - 12.2 -14 <4.2 + 4.0 -13 9.9 - 14.9 -12 3.9 - 10.8 -11 7.3 - 0.2 -10 9.2 + 7.7 - 9 30.1 + 24.4 - 8 7.6 + 13.3 - 7 27.8 + 29.0 - 6 23.1 - 14.0 - 5 2.6 + 8.5 - 4 28.8 + 29.5 - 3 47.7 - 52.0 - 2 5.6 - 6.2 - 1 24.3 - 28.5 0 21.5 - 19.9 1 14.1 - 13.8 2 11.2 - 5.9 3 21.7 + 27.2 4 20.1 + 18.6 5 33.9 + 42.2 6 <2.8 - 4.7 7 21.0 + 19.0 8 24.5 + 23.6 9 24.5 - 24.8 10 <3.5 + 3.9 11 11.1 - 8.1 12 <3.9 + 4.6 13 9.1 - 5.9 14 <4.2 + 7.7 15 32.1 + 25.8 16 <4.4 - 2.3 17 < 4.5 - 3.6 18 <4.4 - 1.3 19 <4.2 + 1.4 - 117 -h k l o lc h k l c h k lo lc 20 3 4.0 _ 3.3 - 7 5 22.2 + 17.5 6 7 <4.1 - 7.8 -19 4 5.9 - 4.4 - 6 28.4 - 17.2 - 5 9.8 - 8.2 -18 <4.3 + 1.1 - 5 9.8 - 16.2 - 4 3.7 + 7.7 -17 <4.4 - 3.4 - 4 3.2 - 2.9 3 13.5 - 13.2 -16 <4.5 - 1.3 - 3 8.2 - 15.8 - 2 12.2 + 8.8 -15 4.4 + 3.3 - 2 4.3 - 12.1 - 1 <3.8 0 -14 7.5 - 9.9 - 1 9.1 + 15.8 0 10.8 + 12.4 -13 5.9 9.0 0 7.4 '+ 10.8 1 <3.8 - 0.3 -12 <4.0 + 2.3 1 9.6 + 9.4 2 21.8 + 22.0 -11 5.5 + 5.6 2 21.0 - 19.9 3 26.6 + 19.6 -10 7.4 - 8.3 3 23.1 + 23.6 4 5.6 + 3.6 - 9 <3.5 - 3.4 4 <3.2 - 2.1 5 8.0 - 7.2 - 8 <3.3 + 4.1 5 18.0 - 20.1 8 8 <4.2 - 0.8 - 7 31.2 + 41.0 6 <3.4 + 2.9 7 14.0 - 11.0 -6 58.5 - 57.2 7 10.0 + 10.0 - 6 12.4 - 16.1 - 5 11.0 5.3 8 18.7 + 15.8 - 5 <4.3 - 1.1 _ 4 23.9 + 27.2 9 <3.8 - 0.6 - 4 12.7 + 13.7 - 3 3.9 + 1.3 10 7.9 +. 5.1 - 3 <4.2 - 0.4 - 2 6.0 - 2.0 11 <4.1 - 3.1 - 2 <4.2 - 7.6 - 1 24.0 26.9 12 16.9 - 15.4 - 1 9.3 + 10.4 0 9.8 + 6.8 13 <4.3 - 1.0 0 < 4.2 0 1 9.8 - 11.6 14 <4.4 + 1.9 1 7.2 + 6.2 2 10.7 - 2.6 15 6.3 + 7.6 2 5.9 - 11.9 3 8.2 + 13.8 - 9 6 5.8 - 5.3 3 10.3 - 6.9 4 14.4 + 18.7 - 8 4.0 + 1.2 4 7.4 + 9.0 5 17.4 + 18.9 - 7 <3.8 + 2.7 5 6.1 - 3.0 6 37.1 + 43.6 - 6 26.7 - 19.8 6 17.3 + 13.2 7 24.5 + 22.3 - 5 <3.6 + 0.1 - 4 9 8.9 - 5.7 8 19.1 + 12.5 - 4 14.3 - 19.1 3 16.5 - 18.9 9 < 3.5 - 5.3 - 3 3.5 - 1.0 - 2 < 4.4 - 2.7 10 3.7 - 6.9 - 2 <3.5 - 3.2 - 1 15.3 - 14.1 11 7.8 + 9.8 - 1 6.8 + 11.1 0 <4.4 0 12 5.7 + 3.9 0 8.4 - 6.8 1 <4.4 0 13 4.2 + 2.9 1 4.8 + 6.6 2 6.2 - 5.0 14 13.0 - 13.7 2 <3.5 - 2.1 3 17.7 + 16.4 15 <4.4 - 2.0 3 <3.5 - 2.2 4 4.4 - 4.8 16 <4.5 + 0.7 4 <3.6 - 5.7 5 7.7 + 9.1 17 4.4 - 8.4 5 5.2 + 1.7 - 4 10 6.2 + 7.0 -16 5 6.3 - 5.3 6 22.2 + 23.4 - 3 <4.4 + 7.0 -15 4.4 - 10.1 7 <3.8 + 1.6 - 2 <4.4 - 4.9 -14 4.4 + 1.9 8 6.0 + 7.2 - 1 4.4 - 7.5 -13 <4.3 - 2.6 9 <44 + 0.6 - 3 11 11.5 - 10.3 -12 10.3 + 8.1 10 <4.2 + 3.2 - 2 < 4.1 - 3,3 -11 <4.1 0.6 11 6 4 + 6.6 - 1 5*8 + 6.6 -10 5.6 + 9.7 - 9 7 12.2 - 4.8 0 5.8 - 3.9 - 9 3.8 - 3*7 - 8 <4.2 - 4.0 1 7.1 + 4.4 - 8 <3.6 + 5.6 - 7 <4.1 - 4.6 2 5.8 - 7.1 00 rH + O vo CM + + CM t-+ rH ? + CTl VO vo.to rH rH to rH to in r- CT\ rH rH to rH in rH O O O O o o o o o o o O O O O o O o O O O O o o O O o O o o o O O O O O O O O O O s 1 Tt rH 1 8 i CM 1 in «t 1 vo to 1 vo to 1 CM to 1 in o + to t~ 1 1 in o r- vo t o t CO in T & cr. o Tt in 1 O to CM in + + cr. T J -+ to in + Tt + + cr* CM + to to in •? CTv C--m + +" to c— rH IO 1 1 CM in 1 1 1 rH rH CVJ B. in ? ? P 1 in in vo 1 1 tO V tO V Tt V Tt CM V W vo CM in CM CM V to to V v tO CM V V CT> CM in in to "<*-c-VO Tt VO 00 rH CT» VO rH CO rH V vO to CO to to l> t-to S to to VO IO rH rH rH VO cr. V cr. to v w H in rH tO in to CT. H vo in rH rH CM to rH to to rH c-c- cr. en ^ V o o o o o o O o o o o o CM CM CM CM CM CM CM CM CM CM CM CM CM Tt *t rt- vo VO VO VO vO vo vo CM rH Tt rH H tO Lf\ t- cr. rH rH O CM rr vo O CM Tt VO CO O rH VO IH 3 O CM CM CM * * CM O CM vo oo o rH CM rH vo rH rH CO rH O CM CM CM O CM Tt vo 00 S r H CO CO CTv (Tv cr> cr, cr. O O rH rH o q rH rH o o o o o O o o O o O O O o O o o o O O O O O O O O O O O o o o tO 00 ? CT> rH t- CO to CM t~ *? t-CM ? CM vo 1 1 cr. CM + + in Tt + + Tt rH rH 1 + +• H-CT. rH rH + + 00 in + + r-CM + in + rH rH + ' O CM + t-CM 1 CM 1 Tj- vo 1 + CM rH + + CT. 1 in CM + CTl VO + rH H + + VO in + vo *=r in in + + r-+ VO o rH + 1 cr. rH rH + CM cr. + cr. to in rH + + CO vo Tt tO rH VO Q Tt to in CM to rH CTl c- o to m o in Tt in VO Tt in Tt v w vo O CO 0 3 3 2 rH rH rH in CO r-VO in CM m V in V in V in V in V in in V v V to V to V in oo CM m tO CM vo H in LO in Tt s VO cr. c- cr. oo in rH o o o o o o o o o o o o o o o o O o o o o o o o o o o o o o o q O o o o o o o O o o O o o o CM Tt vo CO o rH vo rH a o CM rH IO in c- cr. rH rH to rH in rH rH cr. rH o CM Tt VO CO O CM rH rH Tt rH VO rH CO rH rH to in t- cr. a s in rH o CM Tt vO oo o rH Tt Tt Tt «t Tt Tt Tt Tt Tt Tt tn in in in in in tn in in in VO VO vo vo VO VO VO VO VO VO C~ C>- t- c- t~ r- 00 CO CO CO 00 CO 1024 IO r— CM CT. voto t-CM to CO VO CM 11 CM C-+ Tt to i 8 Pi i i IO CM vo Tt 1 1 Tt CM 1 • . ? in in rH VO =91°28*+5 1 . U=l+07.2&3. D x(with Z=2)=l-355> Dm = 1 ' 3 3 gm.cmT3 F(000)=176. Absent spectra: 2 . 2 OkO when k i s odd. Space group may be either P2-j_-C2 or P2!/m-C2h • A preliminary investigation of the c r y s t a l structure (93) has established the correct space group as P2i/m, which requires that the molecule possesses a mirror plane of symmetry perpendicular to the plane of the benzene ring. A c l e a r l y resolved electron-density projection along the short c-axis shows that the molecule (neglecting the hydrogen atoms of the methyl groups) probably has symmetry mm2-C2y Naphtho I b^ cyclobutene (9U) Crystals grown from ethanol solution by slow evaporation occur as transparent plates, the p r i n c i p a l face being (lOO); twinning on (lOO) i s common. The-crystals are highly volatile-and slowly turn milky on exposure to a i r , presumably due to surface decomposition. The high-angle reflexions were a l l too weak to be recorded on Weissenberg photographs,•and t h i s indicates unusually large-thermal vibrations of the atoms i n the c r y s t a l . Crystal Data Naphtho [b] cyclobutene, C 1 2 % 0 ' M=15^.20; , m.p. 8^.5-86°C. Monoclinic, a=l8.0U+0.02, b=5.91+0.01, c=8.13+p.01A, / 3 = 9 2 o 0 ' + 6 ' . U=866-3A3. D x(with Z=U) = l . l 8 l , 1^=1.19 gm.cm"3 F(000)=328. Absent spectra: hk^ when h+k i s odd, ^ 6 h0& when -t i s odd. Space group i s Cd-Cg. (The possible space group C2/c-C2^ - 13U -i s excluded since i t requires the two-fold symmetry axis of the molecule (length ~ 6.3°0 to he p a r a l l e l to the b c r y s t a l axis). Benzocyclobutadienoquinone (95) Crystals obtained from n-propanol solution are yellow prisms bounded by ( l 0 0 \ . The {lio} faces are also w e l l developed. The cry s t a l s slowly decompose into a powder on prolonged exposure to X-rays. Crystal Data Benzocyclobutadienoquinone, CgHi|(C0)2; M=132.11 ; m.p. 132.5°C. Orthorhombic, a=10.72+0.01, b=7.94+0.01, c=7-15+0.Oli. U=608.6&3. D x(with Z=4)=1.442, Dm=lA5 gm- cmT3 F(000)=272. Absent spectra: h O l when 5 11 ,h i s odd, 0k£ when t i s odd. Space group,is Pca2]_-C2v or Pcam-Dgft. cis -1 ,2-Benzocyclobutenedior Dinitrate (95) Crystals grown from a benzene/petroleum ether mixture are transparent prisms elongated along the a-axis, with the (010) and (OOl) faces w e l l developed. Crystal Data cis -1 ,2-Benzocyclobutenediol d i n i t r a t e , C6H^(CH0N02)2; M=226.l4; m.p.110 C. Monoclinic, a=7-41+0.01, b=15.71+0.02, c=8.14+0.01A, jS =98°2'+51. U=938.3A3. D x(with Z=4)=1.601, Dm=1.57 gm.cm"? F(000)=464. Absent spectra: 5 hOc- when h+C, i s odd, OkO when k i s odd. Space group i s P2i/n-C 2^. REFERENCES - 136 -1. International Tables f o r X-r.ay Crystallography. Vol . 1 , 1952; Vol . 1 1 , 1959; V o l . I l l , 1962. Kynoch Press, Birmingham. 2. A.J.C. Wilson, Acta Cryst. 2, 318 (19^9); E.R. Howells, D.C. P h i l l i p s and D. 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Dimensions of the n i t r o x y group i n (a) c i s - 1 , 2 -acenaphthenediol d i n i t r a t e , (b) p e n t a e r y t h r i t o l t e t r a n i t r a t e , and (c) n i t r i c a c i d . - 113 -Figure 38• Average dimensions of the naphthalene moiety of the acenaphthene system. Deviations from the corresponding values i n naphthalene are shown i n brackets; f o r the Qbond distances the deviations are given i n 10 A.