{"@context":{"@language":"en","Affiliation":"http:\/\/vivoweb.org\/ontology\/core#departmentOrSchool","AggregatedSourceRepository":"http:\/\/www.europeana.eu\/schemas\/edm\/dataProvider","Campus":"https:\/\/open.library.ubc.ca\/terms#degreeCampus","Creator":"http:\/\/purl.org\/dc\/terms\/creator","DateAvailable":"http:\/\/purl.org\/dc\/terms\/issued","DateIssued":"http:\/\/purl.org\/dc\/terms\/issued","Degree":"http:\/\/vivoweb.org\/ontology\/core#relatedDegree","DegreeGrantor":"https:\/\/open.library.ubc.ca\/terms#degreeGrantor","Description":"http:\/\/purl.org\/dc\/terms\/description","DigitalResourceOriginalRecord":"http:\/\/www.europeana.eu\/schemas\/edm\/aggregatedCHO","FullText":"http:\/\/www.w3.org\/2009\/08\/skos-reference\/skos.html#note","Genre":"http:\/\/www.europeana.eu\/schemas\/edm\/hasType","IsShownAt":"http:\/\/www.europeana.eu\/schemas\/edm\/isShownAt","Language":"http:\/\/purl.org\/dc\/terms\/language","Program":"https:\/\/open.library.ubc.ca\/terms#degreeDiscipline","Provider":"http:\/\/www.europeana.eu\/schemas\/edm\/provider","Publisher":"http:\/\/purl.org\/dc\/terms\/publisher","Rights":"http:\/\/purl.org\/dc\/terms\/rights","ScholarlyLevel":"https:\/\/open.library.ubc.ca\/terms#scholarLevel","Title":"http:\/\/purl.org\/dc\/terms\/title","Type":"http:\/\/purl.org\/dc\/terms\/type","URI":"https:\/\/open.library.ubc.ca\/terms#identifierURI","SortDate":"http:\/\/purl.org\/dc\/terms\/date"},"Affiliation":[{"@value":"Science, Faculty of","@language":"en"},{"@value":"Chemistry, Department of","@language":"en"}],"AggregatedSourceRepository":[{"@value":"DSpace","@language":"en"}],"Campus":[{"@value":"UBCV","@language":"en"}],"Creator":[{"@value":"Barr, Matthew Ronald","@language":"en"}],"DateAvailable":[{"@value":"2011-10-27T23:26:29Z","@language":"en"}],"DateIssued":[{"@value":"1962","@language":"en"}],"Degree":[{"@value":"Master of Science - MSc","@language":"en"}],"DegreeGrantor":[{"@value":"University of British Columbia","@language":"en"}],"Description":[{"@value":"A general discussion of melting and premelting is given. Crystal structures and phase transitions in the C-forms of stearic, palmitic, myristic and lauric acids and in anhydrous sodium stearate are also discussed. Simple theories of infrared and nuclear magnetic resonance spectrometry are presented.\r\nExperimental difficulties in the use of solid phase infrared spectra are discussed. A detailed study is made of the temperature behaviour of the infrared spectra of the fatty acids in the region from 750 to 700 cm\u00af\u00b9 and over the range from about 70\u00baC below the melting points to about 20\u00baC above them. Three overlapping peaks of different intensity are resolved - 720 cm\u00af\u00b9, about 727 cm\u00af\u00b9, and a peak at higher frequency the position of which varies in the different acids.\r\nThe complete disappearance of the 720 cm\u00af\u00b9 band slightly below the melting point in each acid is taken to indicate a transition, not previously reported, to a disordered phase in which there is considerable molecular motion as evidenced by the phase's liquid-like spectra. The presence of three peaks in the region is discussed on the basis of a simple theoretical expression derived by Snyder for the position of fundamental methylene rocking vibrations. The crystallinities of the acids are estimated from an expression, based on the work of Stein and Sutherland, which involves the apparent integrated absorption intensities of the resolved 720 and 727 cm\u00af\u00b9 bands.\r\nThe extent of premelting is determined. Extensive premelting giving the spectra a liquid-like, but not completely liquid character is found to take place within about 2\u00baC of the melting point.\r\nThe high resolution nuclear magnetic resonance spectra of anhydrous sodium stearate were taken at the limit of their experimental application. The spectra show, however, that the subwaxy, waxy, superwaxy and subneat phases of anhydrous sodium stearate form a structurally similar group (from about 120 to 235\u00baC) with liquid-crystalline properties, while the neat and melt phases also form a structurally similar group (from 235\u00ba C upwards) but with the properties of a liquid.\r\nThe information indicates extensive premelting beginning in the vicinity of 120\u00baC, below which temperature the salt is essentially crystalline, which reaches a climax at 235\u00baC, above which temperature the salt is essentially liquid.","@language":"en"}],"DigitalResourceOriginalRecord":[{"@value":"https:\/\/circle.library.ubc.ca\/rest\/handle\/2429\/38354?expand=metadata","@language":"en"}],"FullText":[{"@value":"A STUDY OP PREMELTING IN THE C-FORMS OP STEARIC, PALMITIC, MYRISTIC AND LAURIC ACIDS BY INFRARED SPECTROSCOPY AND IN ANHYDROUS SODIUM STEARATE BY HIGH RESOLUTION NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY ' by ' MATTHEW RONALD BARR B . S c , U n i v e r s i t y of B r i t i s h Columbia, I960 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department of Chemistry We accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA December, 1962 I n p r e s e n t i n g 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 o f t h e r e q u i r e m e n t s f o r a n a d v a n c e d d e g r e e a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e 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 f o r r e f e r e n c e a n d s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d b y t h e Head o f my D e p a r t m e n t o r b y h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . M. K . Barr D e p a r t m e n t o f C h e m i s t r y The U n i v e r s i t y o f B r i t i s h C o l u m b i a , V a n c o u v e r 3, C a n a d a . Dec. 2 1 , 1962 ABSTRACT A general d i s c u s s i o n of melt i n g and premelting i s given. C r y s t a l s t r u c t u r e s and phase t r a n s i t i o n s i n the C-forms of s t e a r i c , p a l m i t i c , m y r i s t i c and l a u r i c acids and i n anhydrous sodium stearate are al s o discussed. Simple ' the o r i e s of i n f r a r e d and nuclear magnetic resonance spectrometry are presented. Experimental d i f f i c u l t i e s i n the use of s o l i d phase i n f r a r e d spectra are discussed. A d e t a i l e d study i s made of the temperature behaviour of the i n f r a r e d spectra of the f a t t y acids i n the re g i o n from 75>0 to 7 0 0 cm and over the range o o from about 70C below the me l t i n g p o i n t s to about 2 0 C above them. Three overlapping peaks of d i f f e r e n t i n t e n s i t y are resolved - 7 2 0 cm \\ about 727 cm\"\"'\", and a peak at higher frequency the p o s i t i o n of which v a r i e s i n the d i f f e r e n t a c i d s . - 1 The complete disappearance of the 7 2 0 cm band s l i g h t l y below the melting p o i n t i n each a c i d i s taken to i n d i c a t e a t r a n s i t i o n , not p r e v i o u s l y reported, to a disordered phase i n which there i s considerable molecular motion as evidenced by the phase's l i q u i d - l i k e s p e c t r a . The presence of three peaks i n the r e g i o n i s discussed on the basis of a simple t h e o r e t i c a l expression derived by Snyder f o r the p o s i t i o n of fundamental methylene r o c k i n g v i b r a t i o n s . The c r y s t a l l i n i t i e s of the acids are estimated from an expression, based on the work of S t e i n and Sutherland, which involves the apparent i n t e g r a t e d a b s o r p t i o n i n t e n s i t i e s of the r e s o l v e d 720 and 727 cm bands. The extent of p r e m e l t i n g i s determined. E x t e n s i v e p r e m e l t i n g g i v i n g the s p e c t r a a l i q u i d - l i k e , but not completely l i q u i d o c h a r a c t e r i s found to take place w i t h i n about 2C of the me l t i n g p o i n t . The h i g h r e s o l u t i o n n u c l e a r magnetic resonance s p e c t r a of anhydrous sodium s t e a r a t e were taken at the l i m i t of t h e i r experimental a p p l i c a t i o n . The s p e c t r a show, however, that the subwaxy, waxy, superwaxy and subneat phases of anhydrous sodium s t e a r a t e form a s t r u c t u r a l l y s i m i l a r group (from about 120 to 2 3 5\u00b0C ) w i t h l i q u i d - c r y s t a l l i n e p r o p e r t i e s , while the neat and melt phases a l s o form a s t r u c t u r a l l y s i m i l a r group (from 2 3 5 C upwards) but w i t h the p r o p e r t i e s of a l i q u i d . The i n f o r m a t i o n i n d i c a t e s extensive p r e m e l t i n g beginning i n o the v i c i n i t y of 1 2 0 G, below which temperature the s a l t i s o e s s e n t i a l l y c r y s t a l l i n e , which reaches a climax at 2 3 5 C, above which temperature the s a l t i s e s s e n t i a l l y l i q u i d . - x i -ACKNOWLEDGEMENTS Considerable thanks are due to Dr. B.A. D u n e l l who d i r e c t e d t h i s r e s e a r c h . His advice and c h e e r f u l good nature have been h i g h l y a p p r e c i a t e d . Thanks are a l s o due to my c o l l e a g u e s Messrs. A l l a n , Janzen, Krakower and Ware who a l t e r n a t e l y coerced and c a j o l e d the r e l u c t a n t h i g h r e s o l u t i o n spectrometer i n t o working c o n d i t i o n d u r i n g the l a s t p o r t i o n of t h i s i n v e s t i g a t i o n . - i v -TABLE OF CONTENTS CHAPTER ^ PAGE I INTRODUCTION . 1 II MELTING AND PREMELTING 3, D e f i n i t i o n o f Pre m e l t i n g 3 Phase Changes and Premelting 3. M e l t i n g Mechanisms \u00a3 S p e c i f i c Heat Anomalies 6 Premelting as a U n i v e r s a l Phenomenon 7 I I I CRYSTAL STRUCTURES AND PHASE TRANSITIONS 9 A. FATTY ACIDS 9 1. CRYSTAL STRUCTURE 9 Polymorphic Forms 9 C r y s t a l l i z a t i o n of the C-Form 9 C-Form Unit C e l l 10 S u b c e l l s 12 2. PHASE TRANSITIONS 13 B. SODIUM STEARATE 15 1. CRYSTAL STRUCTURE 15 General S t r u c t u r e of F a t t y A c i d S a l t s l\u00a3 Uni t C e l l of Anhydrous Sodium Stearate l\u00a3 Unit C e l l of S i l v e r S tearate 16 2. PHASE TRANSITIONS 17 Complexity of T r a n s i t i o n s 17 D e s c r i p t i o n o f T r a n s i t i o n s 18 CHAPTER PAGE IV GENERAL THEORY 21 A. INFRARED SPECTRA 21 1. ORIGIN 21 Energy of a M o l e c u l a r State and the O r i g i n o f I n f r a r e d S p e c t r a 21 V i b r a t i o n a l Energy and Frequency 22 R o t a t i o n a l Energy and Frequency 23 I n t e n s i t i e s 26 2. CHARACTERISTIC BANDS 29 Number of P o s s i b l e Bands 29 C h a r a c t e r i s t i c Bands of P a r a f f i n Chain Compounds and F a t t y A c i d s 29 D e t a i l e d D i s c u s s i o n o f the Methylene Rocking Band 32 B. NUCLEAR MAGNETIC RESONANCE 3k R e l a t i o n o f Magnetic Moment and Angular Momentum 3^ Energy of I n t e r a c t i o n o f the Magnetic Moment w i t h a Magnetic F i e l d 35 Q u a n t i z a t i o n o f Nuclear O r i e n t a t i o n s and Energy L e v e l s 35 P r e c e s s i o n o f the Nuclear S p i n A x i s 37 Nuclear Spins and Thermal E q u i l i b r i u m w i t h T h e i r Surroundings - R e l a x a t i o n Mechanisms 38 N.M.R. Line Width and Line Second Moment i+3 Temperature Dependence of Line Width and Second Moment - v i -CHAPTER P A G E V EXPERIMENTAL 1+6 A. FATTY ACIDS 1+6 P u r i f i c a t i o n o f A c i d s 1+6 Spectrometer 1+8 S p e c t r a - C o n d i t i o n s and Q u a l i t y 1+8 Temperature C o n t r o l 1+9 P r e p a r a t i o n and Use of P o l y c r y s t a l l i n e Sample Fil m s 50 P o s s i b l e E r r o r s i n the Use of Fi l m s $1 P r e p a r a t i o n o f Samples i n KBr Media 52 Slumping and\/or R e o r i e n t a t i o n of Samples . 53 B. SODIUM STEARATE O r i g i n o f Sample 54-Spectrometer, Recording Equipment and Spect r a Sh Temperature C o n t r o l and E q u i l i b r i u m 55 VI RESULTS 57 A. FATTY ACIDS 57 Use of Apparent Int e g r a t e d A b s o r p t i o n I n t e n s i t y 57 P r e l i m i n a r y S t u d i e s 58 Temperature Behaviour of Expanded Sp e c t r a 58 R e s o l u t i o n of Expanded S p e c t r a 58 Temperature Dependence of the Apparent Inte g r a t e d A b s o r p t i o n I n t e n s i t i e s of Resolved Bands 59 720 cm\" 1 Band 60 - v i i -CHAPTER PAGE 727 cm\" 1 Band 60 High Frequency Band 61 Anomalous Behaviour i n Some M y r i s t i c A c i d Samples 62 L i q u i d - L i k e Character Below the M e l t i n g P o i n t 63 H y s t e r e s i s Loops i n the I n t e n s i t y -Temperature Curves 63 R e s o l u t i o n Above the M e l t i n g P o i n t 61j. V i s u a l O b s ervation of P o l y c r y s t a l l i n e F i l m s 66 B. SODIUM STEARATE 67 \u2022N.M.R. Line Shape 67 N.M.R. Line Width 69 N.M.R. Line Second Moment 69 D i f f i c u l t i e s i n Determining Line Width and Second Moment ' 70 T r a n s i t i o n s Observed by N.M.R. 71 VII DISCUSSION 72 A. FATTY ACIDS 72 C a l c u l a t i o n of Frequencies o f Fundamental Methylene Rocking Bands 72 Anomalous Behaviour i n Some M y r i s t i c A c i d Samples 7k-O r i g i n o f 720 cm\" 1 Doublet S p l i t t i n g 7k Estimate of C r y s t a l l i n i t y i n the F a t t y A c i d s from I n f r a r e d Data ' 76 I - V l l l -CHAPTER B. Discrepancy Between the C r y s t a l l i n i t i e s as Measured by I n f r a r e d and N.M.R. R e l a t i v e C r y s t a l l i n i t i e s o f the F a t t y A c i d s P remelting i n the F a t t y A c i d s SODIUM STEARATE Inference from T r a n s i t i o n s Observed by Line Width and Second Moment Changes N.M.R. I n t e r p r e t a t i o n o f High Temperature Phases o f Sodium Stearate Evidence C o n f l i c t i n g w i t h the I n t e r p r e t a t i o n of the Phases Evidence Supporting the I n t e r p r e t a t i o n of the Phases Premelting i n Sodium Stearate PAGE 80 81 83 89 89 89 91 91+ 96 APPENDIX I APPENDIX I I REPRODUCTIONS OF REPRESENTATIVE EXPANDED INFRARED SPECTRA OF STEARIC, PALMITIC, MYRISTIC AND LAURIC ACIDS REPRODUCTIONS OF REPRESENTATIVE HIGH RESOLUTION NUCLEAR MAGNETIC,RESONANCE SPECTRA OF SODIUM STEARATE 97 ,102 -IX LIST OF ILLUSTRATIONS TO FOLLOW PAGE FIGURE I F o u r i e r P r o j e c t i o n s of the C-Form of L a u r i e A c i d 10 I I The C-Form of L a u r i e A c i d 10 I I I Methylene Chain Packing i n a C-Form F a t t y A c i d 13 IV C-Form F a t t y A c i d Orthorhombic S u b c e l l 13 V Cross S e c t i o n , S i l v e r S t e a r a t e Hydrocarbon Chain Packing. The Suggested Packing f o r Sodium Ste a r a t e 17 VI Methylene V i b r a t i o n s 30 1 VII ^H Nuclear O r i e n t a t i o n s and Energy L e v e l s 36 V I I I Nuclear R e o r i e n t a t i o n 37 IX S t e a r i c A c i d 35\u00b0C 58 X S t e a r i c A c i d 80\u00b0C 58 XI S t e a r i c A c i d Expanded S p e c t r a 58 XII P a l m i t i c A c i d Expanded S p e c t r a 58 XIII M y r i s t i c A c i d Expanded S p e c t r a 58 XIV L a u r i e A c i d Expanded S p e c t r a 58 XV S t e a r i c A c i d R e s o l u t i o n at 3\/T-.2\u00b0C 59 XVI P a l m i t i c A c i d R e s o l u t i o n at 3i|..5\u00b0C 59 XVII M y r i s t i c A c i d R e s o l u t i o n at 33.1\u00b0C 59 XVIII L a u r i e A c i d R e s o l u t i o n at 33 .6\u00b0C 59 XIX S t e a r i c A c i d . Temperature Dependence of the Apparent Int e g r a t e d A b s o r p t i o n I n t e n s i t i e s o f the Resolved Bands 59 XX P a l m i t i c A c i d . Temperature Dependence of the Apparent I n t e g r a t e d A b s o r p t i o n I n t e n s i t i e s o f the Resolved Bands 59 FIGURE TO FOLLOW PAGE XXI M y r i s t i c A c i d (\"Anomalous\"). Temperature Dependence of the Apparent I n t e g r a t e d A b s o r p t i o n I n t e n s i t i e s of the Resolved Bands 59 XXII L a u r i e A c i d . Temperature Dependence of the Apparent I n t e g r a t e d A b s o r p t i o n I n t e n s i t i e s of the Resolved Bands XXIII Sodium Stearate Line Widths XXIV Sodium Stearate Second Moments XXV C r y s t a l l i n i t y o f the F a t t y A c i d s as a F u n c t i o n of Closeness to the M e l t i n g P o i n t 67 67 79 CHAPTER I INTRODUCTION In many compounds c e r t a i n anomalous behaviour i s observed c l o s e to but below the m e l t i n g p o i n t . T h i s behaviour, a t t r i b u t e d to the phenomenon of pr e m e l t i n g , i s found i n , among other substances, s t r a i g h t - c h a i n p a r a f f i n s (1) and s i m i l a r compounds such as the f a t t y a c i d s . As an e x t e n s i o n of pr e v i o u s work (2), s t e a r i c a c i d was re-examined i n more d e t a i l and p a l m i t i c , m y r i s t i c and l a u r i c a c i d s a l s o i n v e s t i g a t e d . In numerous cases of compounds c o n t a i n i n g f o u r or more consecutive CH^ groups, a doublet i n the r e g i o n o f 720 cm 1 i s observed i n the i n f r a r e d spectrum. P r e v i o u s l y i t had been considered that under the above c o n d i t i o n s the band i n t h i s r e g i o n was always a doublet (3), however, more r e c e n t l y i t has been shown t h a t the appearance of the band as doublet or s i n g l e t i s dependent on the sample's c r y s t a l s t r u c t u r e (Jj.)(5). The doublet (as w i l l be noted l a t e r , there may be more than a s i n g l e doublet) has been found by many' i n v e s t i g a t o r s (6)(7)(8)(9). When present, the behaviour of the doublet - s p l i t at low temperature, s i n g l e i n the immediate v i c i n i t y of and above the m e l t i n g p o i n t (8)(9) -suggests t h a t i t may be used as an i n d i c a t i o n of the pr e m e l t i n g i n f a t t y a c i d s . T h i s i n v e s t i g a t i o n was intended to explore t h a t p o s s i b i l i t y and a l s o to determine the . p o s s i b i l i t y of c o r r e l a t i n g i n f r a r e d r e s u l t s w i t h r e s u l t s obtained i n n u c l e a r magnetic resonance s t u d i e s o f the a c i d s (10)(11). - 2 -I n a d d i t i o n t o i n f r a r e d w o r k , h i g h t e m p e r a t u r e (120\u00b0C a n d a b o v e ) p h a s e t r a n s i t i o n s w e r e i n v e s t i g a t e d i n s o d i u m s t e a r a t e . T h e s e o b s e r v a t i o n s w e r e m a d e b y h i g h r e s o l u t i o n n u c l e a r m a g n e t i c r e s o n a n c e t e c h n i q u e s i n a n e x t e n s i o n o f w o r k b e g u n i n t h i s l a b o r a t o r y w i t h b r o a d l i n e m e t h o d s (12). CHAPTER I I MELTING AND PREMELTING Preme l t i n g r e f e r s to changes i n the s o l i d as i t approaches the m e l t i n g p o i n t . These changes a n t i c i p a t e to a l e s s e r degree the changes o c c u r r i n g i n the a c t u a l s o l i d to melt t r a n s i t i o n . There may be present thermodynamic anomalies such as enhanced s p e c i f i c heat, c o e f f i c i e n t of thermal expansion, e l e c t r i c a l conductance (of i o n i c c r y s t a l s ) , or p l a s t i c i t y ( 1 3 ) . Measurements of thermal c o n d u c t i v i t y (111) and e l a s t i c moduli (l\u00a3) a l s o show anomalies a t t r i b u t a b l e to p r e m e l t i n g as do i n f r a r e d ( 2 ) and n u c l e a r magnetic resonance s p e c t r a ( 1 0 ) ( 1 1 ) . I n f o r m a t i o n about phase changes and p r e m e l t i n g may be obtained i n s e v e r a l ways. While heats and temperatures of f u s i o n vary over a very l a r g e range, the e n t r o p i e s o f f u s i o n o f a l l compounds are of the same order - about one to t e n entropy u n i t s ( 1 6 ) . The C l a u s i u s - C l a p e y r o n e q u a t i o n j J L = ( 0 d T ^ v suggests t h a t entropy and volume changes per u n i t mass are parameters t h a t w i l l g ive i n f o r m a t i o n concerning phase changes. Although there e x i s t s no g e n e r a l i z a t i o n concerning the i n f l u e n c e of volume, the Boltzmann r e l a t i o n s h i p , A S = R ^ W ^ v l U ) 1 - k -where and are the number of independent ways the h i g h e r and lower temperature phases r e s p e c t i v e l y may be r e a l i z e d , suggests t h a t the entropy change i s a u s e f u l parameter. E m p i r i c a l c o r r e l a t i o n (16) shows t h a t compounds c o n s i s t i n g of simple u n i t s (atoms, i o n i c c r y s t a l s such as NaCl) and some polyatomic molecules (such as CH^, C C l ^ , C(CH^)^) have low e n t r o p i e s of f u s i o n - about 1.5 to 3 e*i,u.. -Some l a r g e molecules (such as camphor and cyclohexane) which possess compact shapes are a l s o i n t h i s c l a s s . However, some molecules, even though i n c e r t a i n cases s i m i l a r to the p r e c e d i n g , ones, have e n t r o p i e s of f u s i o n of the order of 10 e..u... (C H , CHC1 ). d. 6 3 The d i f f e r e n c e i s found to be i n the method of heat intake before m e l t i n g . The high-entropy substances show unbroken s p e c i f i c heat-temperature curves while the low-entropy substances show one or more s p e c i f i c heat maxima below the m e l t i n g p o i n t . The maxima are r e l a t e d to t r a n s i t i o n s i n the s o l i d i n which the molecules i n c r e a s e t h e i r average symmetry of o r i e n t a t i o n before m e l t i n g . I f there i s o n l y intermediate energy i n t a k e below the m e l t i n g p o i n t there may be only r o t a t i o n about c e r t a i n axes i n the c r y s t a l . The molecule, does not a c q u i r e complete s p h e r i c a l symmetry of r o t a t i o n i n the s o l i d and the entropy of f u s i o n has an i n t e r m e d i a t e v a l u e . This may be the case when onl y p a r t of a molecule r o t a t e s . Considered on the grounds of c l a s s i c a l theory, e q u i l i b r i u m between two phases I s a t t a i n e d when the phases, say s o l i d and l i q u i d , possess the same G-Ibbs f r e e energy per u n i t mass. T r a n s i t i o n from s o l i d to l i q u i d then should imply a d i s c o n t i n u o u s jump between two independent f r e e energy s u r f a c e s which i n t e r s e c t along the t r a n s f o r m a t i o n curve (16). C l a s s i c a l l y no s i n g u l a r i t i e s of behaviour near the m e l t i n g p o i n t are expected. C l a s s i c a l theory, however, d i s r e g a r d s the s t r u c t u r e of the phases, but s t u d i e s i n d i c a t e ( 1 3 ) ( 1 6 ) ( 1 7 ) ( 1 8 ) that the: r e l a t i o n s h i p between s o l i d and melt may i n some cases be very c l o s e . For example, i n the melt molecules of c r y s t a l l i n e p a r a f f i n s are found i n r o u g h l y p a r a l l e l alignment of chains and while long-range order i s l a r g e l y absent there i s i n d i c a t i o n of short-range order ( 1 8 ) . Other s t u d i e s , s p e c i f i c heat and thermal expansion I n v e s t i g a t i o n s ( 1 ) ( 1 6 ) , c o n f i r m the s i m i l a r i t y between s o l i d and melt near the m e l t i n g p o i n t . There may even be domains, analogous to magnetic domains, i n the melt near the t r a n s i t i o n p o i n t ( 1 8 ) . Marked h y s t e r e s i s e f f e c t s may a l s o be present near the m e l t i n g p o i n t ( 1 8 ) . Melts are of course i n g e n e r a l c o n s i d e r a b l y more d i s o r d e r e d than t h e i r s o l i d s . The f a m i l i a r Boltzmann r e l a t i o n s h i p g i v e s a measure o f the i n c r e a s e i n d i s o r d e r upon m e l t i n g . Some c r y s t a l s may assume more than one k i n d of . d i s o r d e r , each type of which p r o v i d e s a p o s s i b l e m e l t i n g mechanism, w i t h the p o s s i b i l i t y of s e v e r a l types of d i s o r d e r o c c u r r i n g s i m u l t a n e o u s l y . The main mechanisms ( 1 3 ) a r e : 1. P o s i t i o n a l m e l t i n g - s t r u c t u r e u n i t s are randomised w i t h r e s p e c t to t h e i r i d e a l l a t t i c e p o s i t i o n s . 2. O r i e n t a t i o n a l m e l t i n g - mutual o r i e n t a t i o n s of - 6 -asymmetric s t r u c t u r e u n i t s are randomised w i t h r e s p e c t to the i d e a l l a t t i c e at low temperature. 3 . G o n f i g u r a t i o n a l m e l t i n g - randomisation of f l e x i b l e molecules ( 1 9 ) which by means of f r e e r o t a t i o n about v a l e n c y bonds may take on more than one c o n f i g u r a t i o n . On f r e e z i n g the, c o n f i g u r a t i o n most e a s i l y packed i n t o the l a t t i c e w i l l be found, but i n the melt i f the energy d i f f e r e n c e s ; are of the order of kT a l l configurations.may be p r e s e n t . T h i s mechanism i s common i n the polymethylene s e r i e s and i n many polymers. ij.. A s s o c i a t i o n a l m e l t i n g - i n the case of c e r t a i n i n o r g a n i c s a l t s the f o r m a t i o n of a s s o c i a t i o n complexes i n c r e a s e s the entropy of f u s i o n . While a l l f o u r mechanisms are important the most common are 1 . and 2 . Mechanisms 3 . and I f . may, f o r the a p p r o p r i a t e compounds, be found i n combination w i t h 1 . and 2 . That i s i n case 3 . the t o t a l entropy of f u s i o n would be S p o i . t l o n a l S o r , R a t i o n a l +\" Sc onf\";^,-. t'.o% (27). The c a r b o x y l group packing determined by Vand was assumed to apply to a l l f a t t y a c i d s (an assumption made f o r some other values a l s o ) . The d i s t a n c e between planes p a s s i n g through the carbon n u c l e i of the end methyl groups was taken to be 2. 18A5 (12). The hydrocarbon chains are arranged w i t h long axes p a r a l l e l . The chains i n g e n e r a l are not p e r p e n d i c u l a r to the p a r a l l e l planes of c a r b o x y l and methyl groups but are t i l t e d at an angle \"C w i t h r e s p e c t to them. A reasonably accurate value of tr may be obtained from the c a l c u l a t e d increment per two carbon atoms and the observed long spacing increment and the assumption of t e t r a h e d r a l G-G bond angles (31). The p e r i o d i c i t y i n the f a t t y a c i d hydrocarbon c h a i n causes s m a l l groups of s t r o n g r e f l e c t i o n s to be r e g u l a r l y d i s t r i b u t e d i n the r e c i p r o c a l l a t t i c e . The groups d e s c r i b e a l a r g e r e c i p r o c a l l a t t i c e (and hence a s m a l l e r d i r e c t c e l l ) and give the t r a n s l a t i o n s between e q u i v a l e n t groups i n a c h a i n and i n adjacent c h a i n s . While the main advantage of - 1 3 -the s m a l l e r c e l l or s u b c e l l i s i n x-ray s t r u c t u r e f a c t o r c a l c u l a t i o n s , i t i s a l s o u s e f u l i n c a l c u l a t i o n s such, as those of i n f r a r e d s p l i t t i n g s due t o \u2022 i n t e r m o l e c u l a r i n t e r a c t i o n s . There are two kinds of s u b c e l l s commonly used i n normal f a t t y a c i d s - orthorhombic and t r i c l i h i c (2 I4 . ) . The t r i c l i n i c s u b c e l l i s used i n the a c i d s having t r i c l i n i c u n i t c e l l s and causes no c o n f u s i o n . The G-form f a t t y a c i d s , however, although they have m o n o c l i n i c u n i t c e l l s and s u b c e l l s , a l s o have very c l o s e to orthorhombic packing of t h e i r hydrocarbon c h a i n s . F i g u r e I I I shows the orthorhombic s u b c e l l f o r an i d e a l i z e d G-form f a t t y a c i d i n which the hydrocarbon c h a i n axes are assumed p a r a l l e l to the c - a x i s and to the a-c plane. Figure IV shows an enlarged view of an orthorhombic s u b c e l l . 2 . PHASE TRANSITIONS The phase t r a n s i t i o n s i n the f a t t y a c i d s are r e l a t i v e l y simple. For the even-numbered a c i d s G i s the s t a b l e form, the t r a n s i t i o n s A -> C and B \u2014 C not being r e v e r s i b l e ( 2 2 ) . However, i t has been r e p o r t e d by Lomer that there i s a spontaneous but very slow t r a n s f o r m a t i o n to the A-form from the C-forms of l a u r i c and m y r i s t i c a c i d s ( 3 2 ) . A check, made on l a u r i c a c i d some years a f t e r the above o b s e r v a t i o n was made, suggested that c o e x i s t i n g w i t h the powdered A-form were c r y s t a l s whose u n i t c e l l dimensions bore a resemblance to both the A and B-forms. The c e l l , dimensions d i d not agree c l o s e l y w i t h e i t h e r A or B but were markedly d i f f e r e n t from the G-form. I t appears t h a t f o r TO FOLLOW PAGE 13 FIGURE III METHYLENE CHAIN RACKING IN A C-FORM FATTY ACID FIGURE IV C-FORM FATTY ACID ORTHORHOMBIC SUBCELL V - 1 1 4 . \" l a u r i c a c i d a t . l e a s t there may be p o s s i b l e a f o u r t h c r y s t a l l i n e form. Study of LomerH^s paper, however, suggests t h a t perhaps the form i s r e l a t e d to the A m o d i f i c a t i o n . T r a n s i t i o n s i n l a u r i c , m y r i s t i c , p a l m i t i c and s t e a r i c a c i d s have been l i s t e d by von Sydow ( 2 2 ) and are reproduced i n Table I I I . Since a l l the forms go to Table I I I . P r e v i o u s l y Observed T r a n s i t i o n s i n S e l e c t e d P a t t y A c i d s A c i d M e l t i n g P o i n t \u00b0C T r a n s i t i o n P o i n t on Heating \u00b0C C B C L a u r i c 4 4 . o 32 M y r i s t i c 5 4 - 2 4 4 P a l m i t i c 6 2 . 9 5 9 S t e a r i c 6 9 . 7 5 4 1+6-the G-form on h e a t i n g , there i s o n l y one m e l t i n g p o i n t f o r a l l the forms of an i n d i v i d u a l a c i d . \u2022 There i s some evidence that the t r a n s i t i o n s may be i n f l u e n c e d by the r a t e o f h e a t i n g . For o i n s t a n c e , the B G t r a n s i t i o n r e p o r t e d at 5 2 . 9 G (note: t h i s i s r e p o r t e d as B C, not A G as by von Sydow) f o r s t e a r i c a c i d takes p l a c e i n a short time. But a B \u2014 ^ G t r a n s i t i o n at 3 5 . 2 \u00b0 C takes about I4.OO hours i n the range 3 0 to 3 5 \u00b0 C ( 3 3 ) . o I t was noted i n the paper r e p o r t i n g the 5 2 . 9 C B \u2014*>\u2022 G t r a n s i t i o n t h a t t h i s value agreed w i t h that o f Thibaud and La Tour who found the B C t r a n s i t i o n at 5 3 . 0 \u00b0 C ( 3 4 ) \u2022 I t would appear then t h a t there i s some u n c e r t a i n t y about the t r a n s i t i o n s as to r a t e of h e a t i n g and even as to which form i s p r e s e n t . F o r t u n a t e l y t h i s d i f f i c u l t y does not a r i s e w i t h the C-form i n v e s t i g a t e d i n t h i s study. - 15 -B. SODIUM STEARATE 1. CRYSTAL STRUCTURE The x-ray a n a l y s i s of s o l i d f a t t y a c i d s a l t s (or soaps) shows t h a t i n g e n e r a l the s a l t s have a l a y e r s t r u c t u r e i n which the c a r b o x y l i o n ends are opposed i n p a r a l l e l p l a n e s . The p a r a l l e l planes are h e l d together by the p o s i t i v e i o n s . The hydrocarbon c h a i n s ! a r e p a r a l l e l to each other w i t h t h e i r l o n g i t u d i n a l axes i n c l i n e d to the plane o f the c a r b o x y l i o n groups at an angle f ( 3 5 ) . Evidence has been obtained t h a t i n c e r t a i n p r o j e c t i o n s the chains o f the A-forra i n at l e a s t potassium caprate are not p a r a l l e l tp each other but form a c r i s s - c r o s s p a t t e r n ( 3 1 ) . Due to v a r y i n g degrees of h y d r a t i o n , a number of d i f f e r e n t m o d i f i c a t i o n s o f the s t r u c t u r e o f sodium s t e a r a t e have been r e p o r t e d . While the forms may be d i s t i n g u i s h e d by x-ray d i f f r a c t i o n ( 3 6 ) , i t i s not always made c l e a r which form i s being r e p o r t e d . The form s t u d i e d by Grant (12) was anhydrous sodium s t e a r a t e . A complete s t r u c t u r a l d e t e r m i n a t i o n o f sodium s t e a r a t e has not yet been made ( 3 7 ) . A v a i l a b l e i n f o r m a t i o n r e p o r t s the u n i t c e l l o f the s a l t at room temperature to be a m o n o c l i n i c p r i s m w i t h the f o l l o w i n g dimensions ( 3 5 ) : - 16 -a 11.16A* b lx.62% d 0 0 1ijJ4 . . 8 3 l t 61 .53\u00b0 The d e n s i t y o f the s a l t s p e c i f i e s two molecules per u n i t c e l l . While sodium s t e a r a t e i s u n c e r t a i n , the s t r u c t u r e of s i l v e r s t e a r a t e i s w e l l d e f i n e d . The s i l v e r s t e a r a t e u n i t c e l l i s t r i c l i n i c w i t h two molecules per u n i t c e l l and the f o l l o w i n g dimension (38): a lx.t>9% 0 b 1J..12A c 50.35^ o C 0 93\u00b059' Y 76\u00b01' z 68\u00b0 The chains are arranged i n the u s u a l manner f o r these s a l t s . The planes o f the hydrocarbon chains are approximately p a r a l l e l to the a-axis and the l o n g i t u d i n a l axes of the chains are t i l t e d In a plane p e r p e n d i c u l a r to the a - a x i s . I t w i l l be mentioned under THEORY, A. INFRARED that the behaviour, doublet or s i n g l e t , of the 720 cm--*- methylene r o c k i n g band may be c o r r e l a t e d w i t h orthorhombic and m o n o c l i n i c or t r i c l i n i c p acking r e s p e c t i v e l y o f the hydrocarbon c h a i n s . In the case o f sodium s t e a r a t e , t h i s band i s s i n g l e (lx). I t i s probable, then, that t r i c l i n i c packing o f chains occurs (th a t i s , a t r i c l i n i c s u b c e l l ) and the arrangement of chains - 17 -In sodium s t e a r a t e may be s i m i l a r to t h a t i n s i l v e r s t e a r a t e . Grant observes (12) that the c e l l c r o s s s e c t i o n s of sodium and s i l v e r s t e a r a t e are almost i d e n t i c a l and concludes t h a t the l a t t e r * s c r y s t a l l a t t i c e i s s u f f i c i e n t l y , s i m i l a r to sodium s t e a r a t e to serve as a model f o r the sodium soap. Prom Vand's data (38) a u n i t c e l l model o f s i l v e r s t e a r a t e may be c o n s t r u c t e d . See F i g u r e V taken from Grant (12). Bond angles were assumed t e t r a h e d r a l throughout the hydrocarbon c h a i n a l t h o u g h there may (38) be s l i g h t d e v i a t i o n s . The C-H bond le n g t h s were taken as 1.0914-$ and the C-G d i s t a n c e s as l.^bX' The hydrocarbon chains were arranged i n the common z i g - z a g c o n f i g u r a t i o n . In F i g u r e V i t was assumed t h a t the carbon z i g - z a g was p a r a l l e l to the a - a x i s . Vand (38) could not determine t h i s e x a c t l y but r e l i e d on comparison w i t h other hydrocarbons. C a l c u l a t i o n s by Grant (12) suggest t h a t Vand's assumption i s c o r r e c t . Once the s i l v e r s t e a r a t e model has been c o n s t r u c t e d i t i s necessary to make the assumption t h a t the sodium s t e a r a t e molecules are packed i n the c r y s t a l l a t t i c e w i t h the same i n t e r m o l e c u l a r d i s t a n c e s as i n the s i l v e r soap (12). \u20222. PHASE TRANSITIONS The phase t r a n s i t i o n s i n the f a t t y a c i d s a l t s are much more complicated than those i n the f a t t y a c i d s . S t e a r i c a c i d shows at the most t r a n s i t i o n s from the forms A or B to C, but sodium s t e a r a t e possesses a formidable a r r a y of t r a n s i t i o n s . The extreme temperatures of the t r a n s i t i o n s as r e p o r t e d by d i f f e r e n t sources are g i v e n i n Table IV. Numerous r e f e r e n c e s f o r the t r a n s i t i o n temperatures are l i s t e d i n Grant (12), from TO FOLLOW PAGE 17 FIGURE V CROSS SECTION, SILVER STEARATE HYDROCARBON CHAIN PACKING. THE SUGGESTED RACKING FOR SODIUM STEARATE FROM REFERENCE 12 - 1 8 -which the t a b l e was taken and w i l l not be reproduced here. Table IV. Phase T r a n s i t i o n s i n Sodium St e a r a t e Name of T r a n s i t i o n Reported Extreme Temperatures o f T r a n s i t i o n \u00b0G Genotypic P o i n t 6 5 \" 70 Gurd to Supercurd 8 9 - 9 3 Supercurd to Subwaxy 1 1 0 - 1 1 7 Subwaxy to Waxy 125-134 Waxy to Superwaxy 165-175 Superwaxy to Subneat 1 9 8 - 2 0 9 Subneat to Neat 2 2 6 - 2 6 2 M e l t i n g P o i n t 2 7 8 - 2 9 8 The genotypic p o i n t at about 7 0 \u00b0 C may be due to i m p u r i t i e s ( 3 9 ) . The curd to supercurd t r a n s i t i o n at around 9 0 \u00b0 G i s u s u a l l y observed o n l y by d i f f e r e n t i a l thermal a n a l y s i s and there appears to be no abrupt change i n d e n s i t y at the t r a n s i t i o n (ifO). The hydrocarbon chains have c o n s i d e r a b l e freedom o f motion i n the supercurd phase. I t i s b e l i e v e d t h a t the l a t t i c e expands i n t h i s phase to a degree s u f f i c i e n t to a l l o w f l e x i n g and t w i s t i n g o f the hydrocarbon chains ( i | ) . The supercurd to subwaxy t r a n s i t i o n occurs around l l l j _ 0 C . At t h i s temperature there i s an abrupt change i n p l a s t i c i t y which i s a t t r i b u t e d to a l o o s e n i n g o f the sodium s t e a r a t e l a t t i c e at the methyl group ends of the hydrocarbon ch a i n s . Thi s would provide e a s i e r s l i p planes ( i l l ) (liZ). - 19 -I n f r a r e d s p e c t r a i n d i c a t e t h a t there are now many more methylene groups f r e e to move i n c o h e r e n t l y about the long a x i s than there were below the t r a n s i t i o n . A l l f i n e s t r u c t u r e due to methylene wagging vanishes and methylene r o c k i n g becomes d i f f u s e ( i i ) . There appears to be a s i g n i f i c a n t change of s t r u c t u r e at the t r a n s i t i o n and a l a r g e degree of motion i s allowed the hydrocarbon chains ( 1 2 ) . The subwaxy to waxy t r a n s i t i o n around 130\u00b0C r e p r e s e n t s a l o s s of c r y s t a l l i n e p r o p e r t i e s . The soap becomes t r a n s l u c e n t (43), there i s an abrupt change i n d e n s i t y (44) and the i n f r a r e d spectrum becomes very c l o s e to t h a t f o r a molten f a t t y a c i d (i|_). There i s s t i l l some s t r u c t u r e , however, f o r sodium s t e a r a t e appears f a i r l y s o l i d i n the waxy phase ( 1 2 ) . However, the above c o n s i d e r a t i o n s suggest t h a t a great decrease i n short range order of the hydrocarbon chains occurs ( 1 2 ) . The waxy to superwaxy t r a n s i t i o n around 165\u00b0C e x h i b i t s a f u r t h e r decrease i n d e n s i t y and an i n c r e a s e i n transparency (43) (k-0) \u2022 A decrease i n the c e l l l o n g spacing suggests (45) that the hydrocarbon chains have more room to f l a i l about than at lower temperatures. The superwaxy to subneat t r a n s i t i o n around 200\u00b0G appears to be s i m i l a r to but of g r e a t e r magnitude -than the preceeding t r a n s i t i o n (I4.O). The subneat to neat t r a n s i t i o n around 250\u00b0G i s marked by f u r t h e r changes i n d e n s i t y and transparency (br3)(br0). Above t h i s t r a n s i t i o n sodium s t e a r a t e w i l l f l o w (46) and c o n s i d e r a b l e changes are b e l i e v e d to be t a k i n g p l a c e at the - 20 -ioni c layer at t h i s t r a n s i t i o n (L|_7) -In the v i c i n i t y of 280\u00b0C the remaining long range structure of the neat form disappears and sodium stearate melts to an i s o t r o p i c l i q u i d (I16) ( l i Q ) . - 21 -CHAPTER IV GENERAL THEORY A. INFRARED SPECTRA 1. ORIGIN. The i n f r a r e d r e g i o n i s the p o r t i o n of the ele c t r o m a g n e t i c spectrum l y i n g between v i s i b l e l i g h t and r a d i o waves. The r e g i o n extends from about 12,5>00 cm 1 -1 to 10 cm but the most commonly used p o r t i o n of the r e g i o n i s from I4.OOO to 600 cm \\ The energy of a mol e c u l a r s t a t e may be w r i t t e n as a sum of f o u r terms E - E e +-EV +- t> + e (S) E e \u00bb E v > > E r where the E , E , E are the e l e c t r o n i c , v i b r a t i o n a l and e v' r r o t a t i o n a l e n e r g i e s r e s p e c t i v e l y of the molecule and t i s an i n t e r a c t i o n term between the e n e r g i e s . Band s p e c t r a which a r i s e from t r a n s i t i o n s between E l e v e l s are not found i n the i n f r a r e d (J4.8). The i n f r a r e d s p e c t r a have t h e i r o r i g i n i n t r a n s i t i o n s between v i b r a t i o n a l and r o t a t i o n a l l e v e l s of the ground e l e c t r o n i c s t a t e s of molecules and are c h a r a c t e r i z e d by the f r e q u e n c i e s or wave len g t h s o f the t r a n s i t i o n s o c c u r r i n g and the i n t e n s i t i e s of those t r a n s i t i o n s . The f r e q u e n c i e s are determined by - 22 -mechanical p r o p e r t i e s of the molecule and the i n t e n s i t i e s by e l e c t r i c a l p r o p e r t i e s ( 4 9 ) . The v i b r a t i o n a l energies of a molecule a r i s e i n the e n e r g i e s of n u c l e i o s c i l l a t i n g about t h e i r e q u i l i b r i u m p o s i t i o n s i n the e l e c t r o s t a t i c f i e l d o f the molecule ( t h a t i s , of i t s e l e c t r o n s and n u c l e i ) . The nature of the f i e l d i s known e x a c t l y only f o r simple molecules f o r which the quantum mechanical problem of the e l e c t r o n i c energies may be s o l v e d . However, an approximate s o l u t i o n may be obtained by r e p l a c i n g the exact p o t e n t i a l energy f u n c t i o n by an approximation which holds f o r s m a l l displacements of the n u c l e i from t h e i r e q u i l i b r i u m p o s i t i o n s . The s i m p l e s t approximation i s the simple harmonic o s c i l l a t o r model (5>0). I f a p o i n t mass i s s l i g h t l y d i s p l a c e d , i n a d i r e c t i o n r , from i t s e q u i l i b r i u m p o s i t i o n , i t w i l l c a r r y out simple harmonic motion w i t h a frequency where k^ i s the f o r c e constant i n the r d i r e c t i o n . In t h i s model the r e s t o r i n g f o r c e ( f o r displacement r , f ^ = - k^r) i s p r o p o r t i o n a l to the f i r s t power of the displacement of the nucleus from i t s e q u i l i b r i u m p o s i t i o n and the p o t e n t i a l energy f u n c t i o n . i s p r o p o r t i o n a l to the square of the displacement ( 4 9 ) . The simple harmonic o s c i l l a t o r model accounts f o r the fundamental v i b r a t i o n from the n o n v i b r a t i n g s t a t e to the s t a t e w i t h one v i b r a t i o n a l quantum e x c i t e d but does not account f o r overtones and combination f r e q u e n c i e s where - -23 -the change i n v i b r a t i o n a l quantum number i s g r e a t e r than one (overtones) or where more than one v i b r a t i o n i s e x c i t e d by one or more quanta. These more complicated t r a n s i t i o n s may be e x p l a i n e d by the use of a p o t e n t i a l energy f u n c t i o n c o n t a i n i n g h i g h e r terms than the square of the displacement (i|9). The p o t e n t i a l energy V may be expanded i n a T a y l o r s e r i e s f o r s m a l l displacements r^. of the mass p o i n t s (note.the p o i n t approximation necessary f o r s i m p l i c i t y ) about the n u c l e i ' s e q u i l i b r i u m p o s i t i o n s . + i (r) where the d e r i v a t i v e s are evaluated at the e q u i l i b r i u m p o s i t i o n s of the mass p o i n t s of the n u c l e i . The f i r s t term i s the value of V when the molecule i s at e q u i l i b r i u m where V q may be taken as zero f o r zero displacement. The second term i s zero s i n c e the slope of the p o t e n t i a l energy s u r f a c e i s zero at e q u i l i b r i u m . The t h i r d term.is the u s u a l p o t e n t i a l energy term f o r the harmonic o s c i l l a t o r and the h i g h e r terms are anharmonicity terms. The terms ( j r y . - J m a y D e regarded {1x8) as g e n e r a l i z e d f o r c e constants which may be determined so as to give the c o r r e c t p o s i t i o n of the fundamental bands i n the spectrum. The f r e q u e n c i e s of pure r o t a t i o n a l s p e c t r a correspond i n the s i m p l e s t approximation to t r a n s i t i o n s between quantized energy l e v e l s of a r i g i d r o t a t o r ( 5 1 ) . The mechanical model depends only on the l o c a t i o n of the - Zli -f i x e d mass p o i n t s r e l a t i v e to the coordinate axes f i x e d i n the molecule. In a l i n e a r molecule there i s o n l y one , 2 p r i n c i p a l moment of i n e r t i a I (I = where e. i s the charge on mass p o i n t k and r i s the k k p o i n t ' s v e c t o r d i s t a n c e from an o r i g i n of c o o r d i n a t e s i n the molecule. In the c a r t e s i a n system - 27 -and i n g e n e r a l M ' = + M - - - - - - - - OS) M t - | e K ^ K - - 0 cm 1 the s p e c t r a of many compounds show comparatively few s t r o n g bands although below t h a t p o i n t there may be a r a t h e r b e w i l d e r i n g a r r a y . F o r t u n a t e l y i t has proved p o s s i b l e to a s s o c i a t e most of the bands and e s p e c i a l l y the more inte n s e ones and those i n the h i g h e r frequency range w i t h s p e c i f i c bonds or groups which cause a b s o r p t i o n at about the same frequency, depending on environment, i n a l l molecules. While the 720 cm\" 1 doublet i s the o n l y i n f r a r e d band c o n s i d e r e d i n the present study, many of the v a r i o u s f r e q u e n c i e s , a r i s i n g as i n d i c a t e d above, are c h a r a c t e r i s t i c o f p a r a f f i n c h a i n compounds. In p a r t i c u l a r the f o l l o w i n g bands are noted. In a l l of a l a r g e mumber of compounds i n v e s t i g a t e d by Pox and M a r t i n (54) two s t r o n g bands corresponding to asymmetrical and symmetrical C-H s t r e t c h i n g modes were observed at 2 9 6 2 cm 1 and 2 8 7 2 cm - 1 r e s p e c t i v e l y . The CH^ group g i v e s ( 5 5 ) two bands, at 2 9 2 6 cm ^ and 2 8 5 3 cm\" 1,which correspond to.in-phase and out-of-phase s t r e t c h i n g v i b r a t i o n s of the hydrogen atoms. I t was found (54)> u s i n g i n t e g r a t e d a b s o r p t i o n areas as a measure of i n t e n s i t y , t h at i n l o n g - c h a i n n - p a r a f f i n s the i n t e n s i t i e s of the GH^ and CH^ bands are d i r e c t l y r e l a t e d to the number of groups p r e s e n t . The CH a b s o r p t i o n was found to change by a constant increment 2 f o r each carbon u n i t i n c r e a s e i n c h a i n l e n g t h . A d e f i n i t e CH^ band.progression s e r i e s was found i n the r e g i o n 1 1 5 0 - 1 3 5 0 cm 1 . I t was noted ( 5 6 ) that i n l a u r i c a c i d , ( C ^ ) . ^ , o n l y three r e c o g n i z a b l e bands could be found. The band head was at 1 1 9 5 cm In h e n e i c o s a n o i c a c i d , (CHg)-^, nine bands were found w i t h the band head at 1 1 8 4 cm 1 . The h i g h frequency end of the band was d i f f i c u l t to d i s t i n g u i s h due to C-0 p e r t u r b a t i o n . Due to hydrogen bending v i b r a t i o n s CH^ deformation g i v e s a b s o r p t i o n near 1 4 6 5 cm 1 . CH^ deformation occurs at 1 4 5 0 cm\" 1 ( 3 ) . The v a r i o u s methylene v i b r a t i o n s - t a r e i l l u s t r a t e d i n F igure VI. In the symmetrical s t r e t c h i n g v i b r a t i o n the hydrogen atoms move towards and away from the carbon atom i n u n i s o n a l t e r i n g the i n t e r a t o m i c d i s t a n c e without changing the valence angle. In the asymmetrical s t r e t c h i n g . TO FOLLOW PAGE 3 0 FIGURE VI M E T H Y L E N E VIBRATIONS FROM REFERENCE 57 c ^H C ^ H SYMMETRICAL STRETCHING ASYMMETRICAL STRETCHING c \\ H ' \\ H -WAGGING TWISTING ' \\ H > DEFORMING ROCKING - 3 1 -v i b r a t i o n one hydrogen approaches the carbon while the other moves away. In the wag v i b r a t i o n the hydrogens move i n unis o n i n and out of the plane of the methylene group. The t w i s t i n v o l v e s movement of the hydrogens i n and out of the plane i n opposite d i r e c t i o n s . There i s a l s o the deformation i n which the hydrogens move a l t e r n a t e l y towards and away from each other i n the plane of the group thus deforming the valence angle. The r o c k i n g v i b r a t i o n i n v o l v e s movement of the hydrogen atoms together i n the plane i n the same d i r e c t i o n thus m a i n t a i n i n g the valence angle. The s t r e t c h i n g and deformation modes are considered to be i n t e r n a l to the methylene group while the rock, wag and t w i s t are e x t e r n a l to the group and r e l a t e d to the r e s t of. the molecule. G e n e r a l l y i n t e r n a l modes i n v o l v e more energy and occur at h i g h e r frequency than e x t e r n a l modes. Asymmetrical s t r e t c h i n g g i v e s r i s e to h i g h e r frequency and more inte n s e a b s o r p t i o n than symmetrical s t r e t c h i n g (57). In a d d i t i o n to the above p a r a f f i n - t y p e v i b r a t i o n s , the f a t t y a c i d s o f course possess the very c h a r a c t e r i s t i c 0-H s t r e t c h i n g v i b r a t i o n . C a r b o x y l i c a c i d s g e n e r a l l y (58) e x i s t i n the dimeric form w i t h s t r o n g hydrogen bonding between c a r b o x y l and h y d r o x y l group. The a c i d s are best r u n as s o l i d s or i n the l i q u i d s t a t e i n order to avoid c o m p l i c a t i o n w i t h the monomer 0-H a b s o r p t i o n . The 0-H v i b r a t i o n g i v e s a broad band near 3000 cm\" 1 and a s a t e l l i t e near 2650 cm 1 . The c a r b o x y l a b s o r p t i o n s f o r s a t u r a t e d - 32 -monoearboxylic a c i d s are found (58) at 1725 cm and 1705 cm 1 i n the s o l i d or l i q u i d s t a t e . S k e l e t a l v i b r a t i o n s are f r e q u e n t l y u n r e l i a b l e , t h a t i s d i f f i c u l t to a s s i g n , however, the ( C H g ^ group where n^lx g i v e s a s t r o n g band near 720 cm - 1. I t a r i s e s (3) from the GH^ r o c k i n g mode and i s t h e r e f o r e not s t r i c t l y a s k e l e t a l mode. Tuot and Lecomte (6) observed the band i n some t h i r t y a l c o h o l s i n which at l e a s t f o u r consecutive CH^ groups were p r e s e n t . Thompson and T o r k i n g t o n (7) assigned the doublet at 721 cm\"\"'\" and 7 3 2 cm 1 In polythene to the presence o f the methylene groups. I t was shown ( 5 9 ) ( 6 0 ) t h a t the v i b r a t i o n s where at r i g h t angles to the carbon c h a i n . Sheppard and Sutherland (59) suggested the range 76O -720 cm\" 1 f o r the band i n v a r i o u s hydrocarbons. The appearance of the band - double or s i n g l e -has been c o r r e l a t e d w i t h orthorhombic f o r the doublet and hexagonal or t r i c l i n i c c r y s t a l s t r u c t u r e f o r the s i n g l e band ( 6 1 ) . E x t e n s i v e r e c e n t work ( 5 ) ( 6 2 )\u2022shows t h a t the doublet i s a s s o c i a t e d w i t h orthorhombic and m o n o c l i n i c c r y s t a l s t r u c t u r e and the s i n g l e t w i t h t r i c l i n i c s t r u c t u r e . In the doublet, the h i g h frequency component has been c o r r e l a t e d w i t h c r y s t a l l i n e behaviour and the low frequency component p a r t l y w i t h amorphous and p a r t l y w i t h c r y s t a l l i n e behaviour of the substance ( 8 ) . C o n s i d e r i n g the CH^ r o c k i n g frequency as a r i s i n g from p e r t u r b a t i o n of the v i b r a t i o n s of the f r e e molecule by the c r y s t a l f i e l d , \u2022 - 33 -i t has been c a l c u l a t e d (63) t h a t the GH^ r o c k i n g frequency at about 720 cm\" 1 should be s p l i t i n t o two, components. The c a l c u l a t i o n by S t e i n , however, does not account f o r the presence bf a t h i r d peak which he h i m s e l f r e p o r t e d present i n some of the compounds i n v e s t i g a t e d ( 8 ) . The t h i r d peak was observed f o r s t e a r i c a c i d i n work (2) p r e c e d i n g - t h i s present i n v e s t i g a t i o n . Subsequent to S t e i n ' s work i t has been r e p o r t e d (5) (61+0 t h a t the s t r o n g doublet i s b e l i e v e d to mask other doublets o r i g i n a t i n g i n hi g h e r normal v i b r a t i o n s of the GH^ r o c k i n g mode. These v i b r a t i o n s may account f o r the t h i r d peak or shoulder on the h i g h frequency side o f the doublet. The band (5) (61+0 i s the o r i g i n o f a s e r i e s o f do u b l e t s , w i t h l e s s e r s p l i t t i n g , which terminates around 1013 cm 1 . - 3 4 -B. NUCLEAR MAGNETIC RESONANCE A d e s c r i p t i v e approach to n u c l e a r magnetic resonance theory may be obtained from a combination of the s i m p l i f i e d v e c t o r model of the nucleus and elementary quantum mechanical concepts. The f o l l o w i n g d i s c u s s i o n i s from Gutowsky (65) u n l e s s s p e c i f i e d otherwise. The mass M and charge e of a nucleus are considered as being u n i f o r m l y d i s t r i b u t e d over the su r f a c e of a s p h e r i c a l s h e l l s p i n n i n g w i t h constant angular momentum P d i r e c t e d along the axis, o f r o t a t i o n of the sphere. The moving charge generates a magnetic f i e l d c y l i n d r i c a l l y symmetrical about the a x i s of r o t a t i o n w i t h the f i e l d being r e p r e s e n t e d by a magnetic moment fS d i r e c t e d along the a x i s . The magnetic moment v e c t o r i s c o l i n e a r w i t h and p r o p o r t i o n a l to the angular momentum v e c t o r a c c o r d i n g to the equ a t i o n where c i s the v e l o c i t y o f l i g h t . The above d e s c r i p t i o n i s a crude approximation from which a c t u a l n u c l e i d i f f e r . A more accurate v e c t o r model would take i n t o account o r b i t a l motions of components w i t h i n the nucleus as w e l l as s p i n n i n g motions to give a r e s u l t a n t angular momentum f o r the nucleus. An unfortunate consequence of the c o u p l i n g of s p i n and o r b i t a l moments i s th a t n u c l e i w i t h an even number of neutrons and protons - 35 -have zero angular momentum and magnetic moment and cannot be i n v e s t i g a t e d by n u c l e a r magnetic resonance (n.m.r). These 12 16 32 i n c l u d e the c h e m i c a l l y important n u c l e i C, 0, and S. 2 6 8 16 F o r t u n a t e l y the ^ H nucleus which cannot be c o n v e n i e n t l y examined by some other methods does possess a magnetic moment and can be s t u d i e d by n.m.r. Indeed, hydrogen i s the p r i n c i p a l nucleus s t u d i e d . To give a more accurate r e p r e s e n t a t i o n o f the n u c l e a r moment, equation (26) i s m o d i f i e d by i n c l u s i o n of the n u c l e a r g f a c t o r analogous to the Lande g - f a c t o r o f atomic s p e c t r a , to give 7~- \u00a32Mc~? - - - - - - - - - - - - - Ml) In f r e e space, the energy o f a n u c l e a r magnet i s . independent of i t s o r i e n t a t i o n . However, i n the presence of a magnetic f i e l d H the n u c l e a r magnet i s s u b j e c t to a torque L a Is which tends to a l i g n i t p a r a l l e l to the f i e l d . I f the magnetic f i e l d i s s t a t i c and o f uniform value H Q over the n u c l e a r magnet, the magnetic i n t e r a c t i o n produces an energy of i n t e r a c t i o n v Ufl where jSH i s the component of fj along H Q. From quantum mechanics elementary p a r t i c l e s e x i s t o n l y i n s t a t e s w i t h p a r t i c u l a r angular momenta (t h a t i s , angular momentum i s q u a n t i z e d ) . From the p r o p o r t i o n a l i t y between angular momentum and magnetic moment i t i s t h e r e f o r e seen that d i s c r e t e magnetic energy l e v e l s occur. - 36 -When the i n t e r a c t i o n of \/T and EQ e s t a b l i s h a d i r e c t i o n i n space f o r a nucleus, then P^ ., the n u c l e a r angular momentum along H^, has a maximum value of Ih\/2fT where I i s the n u c l e a r s p i n , a q u a n t i t y having i n t e g r a l or h a l f i n t e g r a l v a l u e s , and h i s Planck's constant. The allowed o r i e n t a t i o n s are where m is. the magnetic quantum number which may take values Ij \u2022 \u2022 \u2022 \u2022 \u2022 * I \u2022 By s u b s t i t u t i n g components i n equ a t i o n ( 2 7 ) one may o b t a i n from which u s i n g equation (3'Cv) one gets Hence the magnetic energy becomes E = -ngfdnH* - - - - - \u2022 \u2022 ^ The equation (33.) d e s c r i b e s a set of 21 + 1 n u c l e a r o r i e n t a t i o n s and energy l e v e l s which are shown s c h e m a t i c a l l y f o r the ^ H nucleus i n F i g u r e V I I . The s e l e c t i o n r u l e f o r t r a n s i t i o n s between these l e v e l s i s that Am = - 1. Therefore AE = +. g yL\/\u00abHQ. Using the Bohr frequency c o n d i t i o n = h v , i t i s found t h a t the frequency y0 corresponding to an allowed n u c l e a r magnetic energy change i s ^ r g\/frtf.\/h - - - - - - - - - fa) The torque exerted on the n u c l e a r magnetic moment by the f i e l d H Q tends to a l i g n i t w i t h the f i e l d . From Newton's Law, the time r a t e o f change of angular momentum FIGURE VII !H NUCLEAR ORIENTATIONS A N D ENERGY L E V E L S (A) (B) (A) QUANTIZATION OF THE NUCLEAR ANGULAR MOMENTUM \"? AND THE NUCLEAR MAGNETIC MOMENT ~p ALONG r?a (B) NUCLEAR MAGNETIC ENERGY L E V E L S , NOTE T H A T ABSORPTION CORRESPONDS TO Am - 37 -equals the torque Using equations ( 2 7 ) and ( 2 8 ) one f i n d s dt ^ T h i s d e s c r i b e s the p r e c e s s i o n of P about H q w i t h angular v e l o c i t y u~>o where to H^. I f the r f . c u r r e n t produces a l i n e a r l y o s c i l l a t i n g f i e l d such that t h i s i s e q u i v a l e n t to two c i r c u l a r l y p o l a r i z e d f i e l d s r o t a t i n g i n opposite d i r e c t i o n s i n the plane p e r p e n d i c u l a r to o Right c i r c u l a r l y p o l a r i z e d f i e l d . L e f t c i r c u l a r l y p o l a r i z e d f i e l d \\\\y - \\\\M^-kTTvt =~WtM^ %Ttvt (4c) The component having the c o r r e c t sense f o r a g i v e n nucleus (the sense of the Larmor p r e c e s s i o n depends on the s i g n of the magnetic moment w i t h a p o s i t i v e Jf* r e q u i r i n g a l e f t c i r c u l a r l y p o l a r i z e d ) s a t i s f i e s the resonance c o n d i t i o n while the other component has very minor e f f e c t . When a t t e n t i o n i s turned from a s i n g l e nucleus to an assembly of n u c l e i , one must c o n s i d e r the mechanism by which the n u c l e a r s p i n s a t t a i n and m a i n t a i n 1 thermal e q u i l i b r i u m w i t h t h e i r surroundings. N u c l e i are i n s u l a t e d from t h e i r environment (the l a t t i c e ) by the atomic e l e c t r o n s and t r a n s f e r of n u c l e a r magnetic energy to the l a t t i c e i s a comparatively slow pr o c e s s . In p r a c t i c e the e l e c t r o n s must provide some c o u p l i n g w i t h the l a t t i c e (66) or there could be no I n t e r a c t i o n . Since spontaneous emission i s n e g l i g i b l e and induced t r a n s i t i o n s r e q u i r e a magnetic f i e l d o s c i l l a t i n g at the Larmor frequency, i n order that there may be energy t r a n s f e r from n u c l e i to - 39 -l a t t i c e the r e q u i r e d f i e l d s must be produced at the n u c l e i by thermal energy of the l a t t i c e . . Since the p r o b a b i l i t y of an induced t r a n s i t i o n up or down i s the same (66), i f there i s to be a net a b s o r p t i o n of r f . energy there must be an excess of n u c l e i i n the lower energy s t a t e s . A g e n e r a l a n a l y s i s may be made (67), but i t i s simpler t o . c o n s i d e r o n l y the most important case, t h a t of where I = For the hydrogen nucleus, i t may be shown by use of the Boltzmann r e l a t i o n t h a t at thermal e q u i l i b r i u m the r a t i o of the p o p u l a t i o n of the upper-energy s t a t e to the p o p u l a t i o n of the lower-energy s t a t e i s (65) N*\/N, ~- &*f : (41) where k i s Boltzmann's constant, T i s the absolute temperature of the sample and AE i s the energy d i f f e r e n c e between the two s t a t e s . Using equation (33) and (111) one f i n d s t hat i n a f i e l d of 10,000 gauss the r a t i o of the lower s t a t e to the upper s t a t e f o r the p r o t o n i s K\/Nx = 1+gpnHo\/ia + . . . * \/ + \u00a3 X \/ * ' - <4tf T h i s s l i g h t excess of n u c l e i i n the lower s t a t e permits net a b s o r p t i o n of energy i n an r f . f i e l d . When r f . energy i s absorbed by the\"system, some of the excess p o p u l a t i o n i n the lower l e v e l i s t r a n s f e r r e d to the upper l e v e l thus g i v i n g r f . h e a t i n g of the n u c l e a r - s p i n system. Since the n u c l e a r i n s u l a t i o n i s such that the n u c l e i are slow i n l o s i n g t h e i r e x t r a r f . energy to the l a t t i c e , the l o w e r - s t a t e excess p o p u l a t i o n s t e a d i l y decreases u n t i l a steady s t a t e i s - ko -reached. I f the i n s u l a t i o n i s good enough even weak r f . f i e l d s may heat the s p i n system to s a t u r a t i o n . I f the r f . f i e l d i s then rembved, r e l a x a t i o n processes c o o l the s p i n system e x p o n e n t i a l l y w i t h a c h a r a c t e r i s t i c time T-^ , the s p i n - l a t t i c e r e l a x a t i o n time. The us u a l range bf T^ values i s 10 ^ to 10^ \" seconds and they are dependent on temperature, s t a t e and nature o f the sample, and the f i e l d H . o In a d d i t i o n to the s p i n - l a t t i c e i n t e r a c t i o n , there e x i s t s the s p i n - s p i n i n t e r a c t i o n T^ between the n u c l e i themselves. The s m a l l magnetic f i e l d s a s s o c i a t e d w i t h the i n d i v i d u a l n u c l e i may be broken i n t o two p a r t s - the s t a t i c and r o t a t i n g f i e l d s . For a nucleus i n a r i g i d l a t t i c e the n u c l e a r magnetic moment jF produces at a nearby p o i n t Q a l o c a l f i e l d which i s dependent on the d i s t a n c e r and the d i r e c t i o n e o f Q from the nucleus c o n s i d e r e d . The l o c a l f i e l d i s g e n e r a l l y of the order o f a few gauss but reaches 28.2 gauss at a d i s t a n c e of 1 2 i n the case o f the proton. When, as i s u s u a l , the e x t e r n a l a p p l i e d f i e l d H i s very much g r e a t e r than H , the net f i e l d i s approximately HI-HI + H^ < \u00ab 3 ) where H, i s the component of K* along H . Since i t has JL-L \u2022 . o been found t h a t - \u00a3 - \u00a3 ( 3 ^ * - \/ ) - - - - - - - (44-) then rC = TTe \u00b1 X - ( 3 ^ e - \/ ) (As). - 41 -Prom equation (l|f>) i t i s apparent t h a t there e x i s t s a s p l i t t i n g (spread) i n the a p p l i e d f i e l d H which w i l l give e the resonant f i e l d H . For samples c o n t a i n i n g i s o l a t e d o p a i r s of n u c l e i w i t h I = ^, the resonance at a f i x e d frequency would be s p l i t i n t o two equal components separated by a d i s t a n c e of ~^(3c+o*-0-1) ; gauss. For p a i r s o r i e n t e d a t random, as i n a powder, a broadened resonance doublet occurs; while f o r many, i n t e r a c t i n g , randomly o r i e n t e d n u c l e i a r o u g h l y b e l l - s h a p e d a b s o r p t i o n curve r e s u l t s . I f the n u c l e i are i n motion r a t h e r than s t a t i o n a r y , the i n t e r n u c l e a r d i s t a n c e s and d i r e c t i o n s w i l l v ary w i t h time. The z-component of the r e s u l t i n g magnetic f i e l d i s g i v e n by The changing l o c a l f i e l d s produce m o t i o n a l narrowing by averaging out the s p i n - s p i n broadening. For example, f o r a p a i r of .nuclei r o t a t i n g w i t h f i x e d r , O i s a f u n c t i o n of time. . I f the r o t a t i o n occurs u n i f o r m l y over a l l d i r e c t i o n s and occurs r a p i d l y (that i s ; the frequency of motion i s of the order of the frequency w i d t h of the resonance) the average value of c^o^e^) i s 1 \/3 and e q u a t i o n (2+6) reduces to zero and r o t a t i o n a l narrowing has taken place w i t h the r e s u l t t h a t rt - TTe \u00ab- Hg* = Hi M The r o t a t i n g components of the l o c a l magnetic f i e l d s a l s o add to broadening of the resonance. A p a i r of - i i 2 -i d e n t i c a l n u c l e i , w i t h I = j\u00a7-, i n the same f i e l d H precess o at the same Larmor frequency. Each nucleus has a component (the component p e r p e n d i c u l a r to the f i e l d d i r e c t i o n H^), o f the magnetic moment, which r o t a t e s i n the x-y plane. These r o t a t i n g components produce a s p i n -exchange or s p i n - s p i n c o l l i s i o n between the n u c l e i i n the p a i r by g e n e r a t i n g r o t a t i n g l o c a l f i e l d s H,\u00a3 at each nucleus. The f i e l d s produce a simultaneous r e o r i e n t a t i o n o f both n u c l e i by i n t e r c h a n g i n g i n d i v i d u a l e n e r g i e s yet con s e r v i n g t o t a l energy. The spin-exchange l i m i t s the l i f e t i m e z a t of the n u c l e a r s t a t e s and by the Heisenberg p r i n c i p l e g i v e s a r e l a t e d u n c e r t a i n t y \/ S E i n the energy. A n u c l e a r s p i n w i l l precess about Ex^ and have an energy i n . t h e f i e l d o f ^ E - = - gjJnVU ----- -.- (48^ \u2014 H,_g i s of the order of magnitude of and g i v e s a broadening i n resonance comparable to that o f the s t a t i c f i e l d s . The spin-exchange e f f e c t i s , however, only important between n u c l e i o f the same s p e c i e s . The g e n e r a t i o n o f o s c i l l a t i o n s i n the l o c a l magnetic f i e l d by l a t t i c e motions p r o v i d e s an important mechanism f o r s p i n - l a t t i c e r e l a x a t i o n . An exact a n a l y s i s of the s p i n - l a t t i c e mechanism demands a knowledge of the time dependence of n u c l e a r p o s i t i o n . I f t h i s i s known, then the o s c i l l a t i o n s at the Larmor frequency i n the x-y plane l o c a l f i e l d s may be c a l c u l a t e d and t h e i r e f f e c t on ^ deduced ( 6 7 ) . - 43 -Since the n u c l e a r surroundings i n f l u e n c e the width and shape of n u c l e a r magnetic resonance l i n e s (68), t h i s may i n v e s t i g a t e d . T h e o r e t i c a l l i n e shapes have been c a l c u l a t e d and v e r i f i e d f o r two-spin (69), t h r e e - s p i n (70)(71),- and f o u r - s p i n (72) systems. However, the complexity o f i n t e r a c t i o n s i n many-spin systems (the complexity of even the f o u r - s p i n system i s form i d a b l e ) p r e c l u d e s c a l c u l a t i o n . I t should be noted t h a t even f o r few-spin systems the resonance l i n e shape i n powder samples i s very much broadened (73) and onl y i n t e r n u c l e a r d i s t a n c e i n f o r m a t i o n may be obt a i n e d . For t h i s reason, s i n g l e c r y s t a l s t u d i e s are o f t e n employed i n n.m.r. s t r u c t u r a l a n a l y s e s . Although q u a n t i t a t i v e i n f o r m a t i o n cannot always be obtained from the l i n e shapes, v a l u a b l e q u a l i t a t i v e i n f o r m a t i o n can f r e q u e n t l y be obtained. Line width, the measurement u s u a l l y made on n.m.r. a b s o r p t i o n l i n e s , may be d e f i n e d e i t h e r as the di s t a n c e between the maximum and minimum slope on the a b s o r p t i o n curve or the width at one-half maximum amplitude on the curve. l i n e shapes f o r complex s t r u c t u r e s , Van V l e c k has shown (74) t h a t the second moment of the n.m.r. l i n e can be r e l a t e d to a g i v e n s t r u c t u r a l model. The second moment i s d e f i n e d (75) be used to provide s t r u c t u r a l i n f o r m a t i o n about the system Although i t i s d i f f i c u l t to determine t h e o r e t i c a l as - 44 ~ where f(H) i s the li n e - s h a p e f u n c t i o n at any value o f the f i e l d H and H i s the value of H at the cente r o f the o a b s o r p t i o n l i n e . The r e l a t i o n between second moment of a powdered c r y s t a l and the d i s t a n c e r ^ k between r e s o n a t i n g atoms was c a l c u l a t e d t h e o r e t i c a l l y by Van Vl e c k and r e w r i t t e n by Gutowsky ( 7 5 ) as where the s u b s c r i p t f r e f e r s to n u c l e i other than r e s o n a t i n g n u c l e i which nonetheless c o n t r i b u t e to broadening. N r e p r e s e n t s the t o t a l number of r e s o n a t i n g n u c l e i i n the p a r t i c u l a r sub-group ( u n i t c e l l , e t c . ) to which the broadening Is a t t r i b u t e d . Attached to t h i s e q u a t i o n are the c o n d i t i o n s ( 7 5 ) t h a t the l a t t i c e must be r i g i d at the temperature at which the experiment i s c a r r i e d out; the n u c l e i must not move a p p r e c i a b l y i n time o f order T^ (that i s the l o c a l c o n f i g u r a t i o n remains s t a t i o n a r y f o r up -k - 5 to 10 to 10 seconds, zero p o i n t motion i s ignored ( 7 ) ) and t h a t there must not be paramagnetic ions present i n g r e a t e r atomic r a t i o of paramagnetic i o n to r e s o n a t i n g i o n -6 than 10 to one. I f i t i s assumed t h a t i n t e r a c t i o n s of * magnetic n u c l e i other than protons are n e g l i g i b l e , then the second moment reduces ( 7 4 ) to A H ^ = - - (St) where r i s the d i s t a n c e between any two protons j and k. When the temperature dependence of n.m.r. phenomena i s observed, abrupt changes i n l i n e width and second moment may o f t e n be found. When frequency of - kS -rotation, which i s influenced by temperature, i s of the order of the n.m.r. li n e width, the li n e width and second moment decrease. Such changes frequently correspond to phase tra n s i t i o n s (76) and second moments can be estimated for these transitions by the various second moment equations. In general, the changes i n \/ l i n e width and second moment are useful i n estimating the onset and extent of molecular motions and of determining the type of motion i t s e l f (76). - ke -CHAPTER V EXPERIMENTAL A. FATTY ACIDS Kodak white l a b e l grade s t e a r i c , p a l m i t i c , m y r i s t i c and l a u r i c a c i d s were p u r i f i e d by repeated low temperature c r y s t a l l i z a t i o n s (77)- Q u a n t i t i e s r anging from 25 to 50 gms. of a c i d were d i s s o l v e d i n d i l u t e s o l u t i o n i n hot, f r e s h l y d i s t i l l e d reagent grade acetone. The beaker c o n t a i n i n g the a c i d s o l u t i o n was then p l a c e d i n a dewar c o n t a i n i n g a dry ice-acetone bath at a s e l e c t e d temperature. The temperatures used f o r c r y s t a l l i z a t i o n are l i s t e d i n Table V. Table V. C r y s t a l l i z a t i o n Temperatures A c i d C r y s t a l l i z a t i o n Temperature \u00b0C S t e a r i c -20 P a l m i t i c -15 M y r i s t i c -20 L a u r i c -30 The s o l u t i o n was s t i r r e d m e c h a n i c a l l y f o r about an hour and then the a c i d was permitted to s e t t l e , the s o l v e n t f i l t e r e d o f f and the a c i d s pressed between f i l t e r paper to remove excess s o l v e n t before d r y i n g i n a vacuum d e s s i c a t o r over P 0 . The process was repeated u n t i l the f r e e z i n g p o i n t s 2 5 were found to be constant f o r s u c c e s s i v e r e c r y s t a l l i z a t i o n s - 47 -( p r e f e r a b l y at l e a s t three s u c c e s s i v e constant f r e e z i n g p o i n t s ) . P u r i f i c a t i o n of the a c i d s depends on the q u i t e d i f f e r e n t s o l u b i l i t i e s of the homologous a c i d s at low temperatures. The l e a s t s o l u b l e a c i d ( s t e a r i c ) can be obtained w i t h no d i f f i c u l t y . More s o l u b l e a c i d s may a l s o be obtained in'..a pure s t a t e i f l e s s s o l u b l e i m p u r i t i e s are present i n s m a l l amount as was the case w i t h the r e l a t i v e l y pure s t a r t i n g m a t e r i a l s ( l e s s than i m p u r i t y ) used. As an index of p u r i t y , m e l t i n g and f r e e z i n g p o i n t s were determined. M e l t i n g p o i n t s were done on a hot-o stage microscope h e a t i n g at about 0.2C per minute. F r e e z i n g p o i n t s were taken from the p l a t e a u x of temperature-time c o o l i n g curves. The observed m e l t i n g and f r e e z i n g p o i n t s are compared i n Table VI to those l i s t e d by Markley (78) Table VI. M e l t i n g and F r e e z i n g P o i n t s of S e l e c t e d F a t t y A c i d s A c i d Observed Reported M e l t i n g F r e e z i n g M e l t i n g F r e e z i n g Point\u00b0C Polnt\u00b0C Point\u00b0C Point\u00b0C S t e a r i c 69.5-69.8 69-4 69.6 69.3 P a l m i t i c 63.0 62.7 63.1 62.8 M y r i s t i c 54-3-54-5 54-1 53 . 9 * 54-1 L a u r i c lili. 0-44.3 43.7 44-2 43-9 -\u00ab-54'4 l i s t e d by r e f e r e n c e (79) - 48 -S p e c t r a were run on a Perkin-Elmer Model 21B double beam i n f r a r e d spectrometer. I t was found t h a t normal q u a l i t a t i v e o p e r a t i n g c o n d i t i o n s (80) gave s a t i s f a c t o r y r e s o l u t i o n . P r e l i m i n a r y s t u d i e s were made of the s p e c t r a of the a c i d s over the range liOOO to 600 cm\" 1 from about 30\u00b0C o o to about 90 G f o r s t e a r i c a c i d and at 30 C o n l y f o r the other a c i d s . Expanded s p e c t r a (50 cm per 100 cm 1 ) were run from 750 cm 1 to 700 cm 1 to cover the r e g i o n of i n t e r e s t . For expanded s p e c t r a a scanning.rate o f about 50 cm 1 i n seven minutes was used. For a l l expanded s p e c t r a , the a b s o r p t i o n was set at a s u i t a b l e p o i n t (about 0.05 o p t i c a l d e n s i t y at 750 cm ^, the p o i n t o f minimum ab s o r p t i o n ) and l e f t untouched f o r the d u r a t i o n of each set o f experimental runs on an a c i d . S p e c t r a were recorded on a l o g a r i t h m i c o p t i c a l d e n s i t y g r i d c h a r t and each curve was t r a c e d at l e a s t twice. Except when taken e x a c t l y on a t r a n s i t i o n p o i n t when e q u i l i b r i u m had not been f u l l y e s t a b l i s h e d the curves always agreed very c l o s e l y . V a r i a t i o n between curves was of the order of 0.005 o p t i c a l d e n s i t y u n i t s about the magnitude of the noise f l u c t u a t i o n s i n the curves. P r e l i m i n a r y runs i n the 750 - 700 cm 1 range of samples both as f i l m s c r y s t a l l i z e d between sodium c h l o r i d e p l a t e s and as s o l i d s o l u t i o n s i n potassium bromide d i s c s were r u n from about 30\u00b0C (the approximate machine temperature) up past the m e l t i n g p o i n t and back to 30\u00b0G. - 4 9 -P i n a l runs, which were made w i t h f i l m s between s a l t p l a t e s , o were commenced at 30 C, taken down i n s u c c e s s i v e steps to about 6 0 C \u00b0 below the m e l t i n g p o i n t , then r a i s e d i n o s u c c e s s i v e steps to about 20C above the m e l t i n g p o i n t and then taken back by steps to 30\u00b0C. Temperatures were changed by s m a l l increments -about 0 . 5 0 \u00b0 when near the m e l t i n g p o i n t . Since even f o r changes of the order o f l ^ C 0 e q u i l i b r i u m was reached i n about 15 minutes, i t was con s i d e r e d adequate to al l o w some 20 to 25 minutes between runs. As a check some s p e c t r a were taken c l o s e to the m e l t i n g p o i n t a f t e r the standard p e r i o d at e q u i l i b r i u m and then l e f t f o r s e v e r a l hours at the same temperature before r e p e a t i n g the s p e c t r a . No change was observed. Temperatures were measured at the beginning and end of each i n d i v i d u a l run and were found to vary by l e s s than -0.2C . Heating was done w i t h a standard Perkin-Elmer e l e c t r i c a l h e a t i n g u n i t . The u n i t was designed f o r use i n the temperature range 100 to 200\u00b0C and was d i f f i c u l t to c o n t r o l i n the range r e q u i r e d . However, by keeping the u n i t ' s h e a t i n g c o n t r o l f i x e d , adequate c o n t r o l c o u l d be achieved w i t h a v a r i a c i n t o which the u n i t was plugged. For a d d i t i o n a l c o n t r o l a constant v o l t a g e transformer was used to supply the c u r r e n t . An e l e c t r i c a l l y heated brass r i n g i n a ceramic mounting h e l d the s a l t p l a t e s or the brass KBr d i s c h o l d e r . The c o o l i n g device c o n s i s t e d of a simple box, open at both ends, c o n s t r u c t e d to enclose the sample beam - 5o -path. Cold n i t r o g e n vapour was allowed to flow over the sample p l a t e s from an i n l e t tube above the p l a t e s and j u s t out of the beam path. E i t h e r tank n i t r o g e n passed through a c a l c i u m c h l o r i d e tower and cooled by being passed through a copper c o i l immersed i n a acetone-dry i c e or l i q u i d n i t r o g e n bath or nitrogen.vapour b o i l e d o f f from l i q u i d n i t r o g e n was used. As noted above, s p e c t r a were-run w i t h samples both as f i l m s between s a l t p l a t e s and as s o l i d s o l u t i o n s i n KBr d i s c s . Temperatures were recorded f o r the f i l m s by a copper-constantan thermocouple p l a c e d i n a groove between the opposing f a c e s o f the s a l t p l a t e s . The couple was i n the instrument beam and i n contact w i t h the sample. For the KBr d i s c s a copper constantan thermocouple was so l d e r e d i n t o the brass p e l l e t - h o l d e r (couple and h o l d e r were c a l i b r a t e d as one u n i t ) . Because of temperature g r a d i e n t s i n the KBr p e l l e t h o l d e r temperatures were considered accurate to not b e t t e r than 3C\u00b0, however, the temperatures f o r the f i l m s were considered to be good to not worse than -0.5C\u00b0. F i l m s were prepared by m e l t i n g the a c i d on a heated NaCl p l a t e , p r e s s i n g a second p l a t e on top, and r a p i d l y c o o l i n g the p l a t e s w i t h a stream o f dry compressed a i r . A double t h i c k n e s s NaCl p l a t e was used i n the r e f e r e n c e beam to compensate f o r r a d i a t i o n s c a t t e r i n g and r e f l e c t i o n . In order to avoid excessive absorbance by too t h i c k a sample, t h i n spacers of about 0.01 to 0.03 mm - 5 1 -t h i c k n e s s were used. However, uniform sample t h i c k n e s s was not achieved and the bother of h a n d l i n g the f r a g i l e spacers was such t h a t samples were run without them. Due to d i f f i c u l t y i n p o l i s h i n g the p l a t e s i n t o plane, p a r a l l e l s u r f a c e s , i t proved impossible to o b t a i n a f i l m of constant t h i c k n e s s . In a d d i t i o n , as the f i l m cooled from the melt, areas of c r y s t a l o r i e n t a t i o n were apparent between the p l a t e s w i t h obvious inhomogeneities i n c l u d i n g the presence of some areas f r e e of a c i d . Very c o n s i d e r a b l e e r r o r may be i n t r o d u c e d due to inhomogeneity i n the sample ( 5 3 ) . When the absorbing m a t e r i a l i s composed of macro p a r t i c l e s separated by r e g i o n s of h i g h transmittance and when-there i s no u n i f o r m i t y of sample t h i c k n e s s , the r e s u l t s do not f o l l o w c l o s e l y the laws governing a b s o r p t i o n of r a d i a t i o n by i s o t r o p i c m a t e r i a l s . For example, d e v i a t i o n s from Beer's Law occur i n inhomogeneously d i s p e r s e d systems. The presence of the s m a l l , f r e e l y t r a n s m i t t i n g areas found i n the samples would be expected to give r i s e to a c o n s i d e r a b l e d i f f e r e n c e between true and observed o p t i c a l d e n s i t y ( 5 3 ) . With 10% f r e e l y t r a n s m i t t i n g space and an o p t i c a l d e n s i t y of 1 . 0 , d e v i a t i o n s of 2 0 - 2 5 $ between true and experimental o p t i c a l d e n s i t i e s occur. However, below an o p t i c a l d e n s i t y of about 0 . 3 there w i l l be l i t t l e d i f f e r e n c e f o r up to 20% c l e a r space which i s q u i t e an extreme case. Sample t h i c k n e s s to give values of around 0 . 2 to 0 . 3 was g e n e r a l l y used i n t h i s i n v e s t i g a t i o n . - 52 -To avoid the marked o r i e n t a t i o n a l e f f e c t s noted In the f i l m s , samples were prepared i n KBr d i s c s as d e s c r i b e d by K i r k l a n d ( 8 l ) . P e l l e t s were prepared w i t h d r i e d , Harshaw o p t i c a l grade KBr. A c i d s s t o r e d i n a d e s i c c a t o r were melted under vacuum f o r up to 10 hours to remove any moisture or s o l v e n t s that might be present ( t h i s was a l s o done f o r the f i l m s ) q u i c k l y s o l i d i f i e d , ground i n a mortar, shaken m e c h a n i c a l l y w i t h KBr f o r 15 minutes, and pressed i n a Perkin-Elmer die at 20,000 p s i . T h i s gave an inhomogeneously appearing ( t r a n s p a r e n t and opaque r e g i o n s ) p e l l e t . The p e l l e t was ground up, reshaken and r e p r e s s e d to give a homogeneous, v i s u a l l y opaque p e l l e t . To e l i m i n a t e the p o s s i b i l i t y of moisture being p i c k e d up from the atmosphere, the procedure was c a r r i e d out i n a dry box, but the same type p e l l e t was obtained and i t was concluded t h a t the appearance of the p e l l e t was due to the sample, not moisture. Since the 720 cm 1 r e g i o n i s near the end of the KBr range, a pure KBr p e l l e t was used i n the re f e r e n c e beam to compensate f o r any change i n a b s o r p t i o n and to compensate f o r r a d i a t i o n s c a t t e r i n g and r e f l e c t i o n at the sample p e l l e t ' s s u r f a c e . Although KBr d i s c samples are sometimes d e s c r i b e d as- s o l i d s o l u t i o n s , the l i n e a r dimensions of the i n d i v i d u a l absorbing p a r t i c l e s are i n excess of 10oi\u00a3 and hence each contains s e v e r a l u n i t c e l l s of c r y s t a l (53). Consequently even i n KBr d i s c s , one i s d e a l i n g w i t h s o l i d phase s p e c t r a s u b j e c t to o r i e n t a t i o n a l e f f e c t s s i m i l a r to but i n - 5 3 -somewhat l e s s e r extent than that i n c r y s t a l l i n e f i l m s between p l a t e s . As the s p e c t r a obtained i n t h i s work were qu i t e s i m i l a r whether as f i l m or KBr d i s c , but s i n c e temperatures were more a c c u r a t e l y known f o r the f i l m s , most, i n c l u d i n g the f i n a l runs, were w i t h f i l m s . Since a d j u s t i n g the spectrometer's o p t i c a l system f o r use w i t h a h o r i z o n t a l c e l l r e q u i r e d about one h a l f a day's time both before and a f t e r runs, a v e r t i c a l c e l l was used to a v o i d tying-up the spectrometer more than was a b s o l u t e l y necessary. T h i s meant that the use of f i l m s d i d i n t r o d u c e one c o m p l i c a t i o n ; the p o s s i b i l i t y of slumping a f t e r m e l t i n g . In some cases slumping or perhaps r e o r i e n t a t i o n of the sample on.the p l a t e s on c o o l i n g from the melt has occurred, but t h i s has merely produced a p a r a l l e l displacement of the curve obtained. R e p e t i t i o n o f runs was made on d i s p l a c e d curves f o r l a u r i c a c i d to determine i f the curves could be r e t r a c e d . (See RESULTS, A. PATTY ACIDS.) - Sk B. SODIUM STEARATE The sodium s t e a r a t e used was an .anhydrous sample (M. p t . 275-280\u00b0C) prepared by Grant i n an e a r l i e r i n v e s t i g a t i o n (12). Sp e c t r a were run oh a V a r i a n Model Vl|35>2 h i g h r e s o l u t i o n n u c l e a r magnetic resonance spectrometer o p e r a t i n g at liO Mc. A minimum of s i x s p e c t r a were recorded a t each temperature - three sweeps up f i e l d and three down f i e l d . I n d i v i d u a l s p e c t r a at a constant temperature were not c l o s e l y r e p r o d u c i b l e . The extent of the d e v i a t i o n s w i l l be noted under RESULTS, B. SODIUM STEARATE. Due to the c o n s t r u c t i o n of the sample dewar i t was impossible to s p i n the sample to o b t a i n the best p o s s i b l e f i e l d . The s p e c t r a were checked at each temperature f o r s a t u r a t i o n broadening. The sweep r a t e was c a l i b r a t e d at each temperature by imposing side bands on the main s i g n a l w i t h a Hewlett Packard Model 200 CD o s c i l l a t o r . The o s c i l l a t i o n f r e q u e n c i e s were measured w i t h a Hewlett Packard Model 522B e l e c t r o n i c counter. The a b s o r p t i o n l i n e shapes were recorded on a Leeds and Northrup Speedomax H r e c o r d e r except f o r s p e c t r a taken at three temperatures. For the three temperatures a m a l f u n c t i o n i n the V a r i a n V-K3506 super s t a b i l i z e r made i t i mpossible to sweep the f i e l d and s p e c t r a were photographed on a Dumont Type 30ij.-AR o s c i l l o s c o p e w i t h a Dumont o s c i l l o g r a p h - r e c o r d camera. - 55 -S p e c t r a were recorded from about 120\u00b0C to about 300\u00b0C. The s p e c t r a were not a l l recorded i n sequence of i n c r e a s i n g temperature, but the sample was always brought to thermal e q u i l i b r i u m by h e a t i n g , never by c o o l i n g , i n order to avoid any p o s s i b l e c o m p l i c a t i o n s from h y s t e r e s i s e f f e c t s i n the v i c i n i t y of phase t r a n s i t i o n s . A minimum of two hours was always allowed between runs i n order to achieve thermal e q u i l i b r i u m . Due to r e s t r i c t i o n s on the a v a i l a b i l i t y of the equipment, i t was not p o s s i b l e to leave the sample at e q u i l i b r i u m f o r s e v e r a l hours when near a t r a n s i t i o n p o i n t as was done by Grant (12). The p o s s i b i l i t y of n o n - e q u i l i b r i u m c o n d i t i o n s near a phase t r a n s i t i o n was i n v e s t i g a t e d i n some cases by r e p e a t i n g s p e c t r a a f t e r d i f f e r e n t p e r i o d s of time at a constant temperature. I t was found that the two hour p e r i o d was s a t i s f a c t o r y except when e x a c t l y on a t r a n s i t i o n p o i n t where a f o u r hour p e r i o d was adequate. However, even w i t h i n as c l o s e as 2C\u00b0 to a t r a n s i t i o n the two hour p e r i o d was s a t i s f a c t o r y . Hence at worst a t r a n s i t i o n would only be s l i g h t l y d i s p l a c e d due to n o n - e q u i l i b r i u m c o n d i t i o n s . The sample was heated by a stream of compressed a i r f l o w i n g over a r e s i s t a n c e wire element i n a t i n can heate r c o n s t r u c t e d by a co-worker. The heated stream was passed through a dewar l e a d i n t o the sample dewar. The stream passed down over the sample and out a r e t u r n passage. The temperature was recorded by a copper-- 5 6 -c o n s t a n t a n t h e r m o c o u p l e p l a c e d i n t h e r e t u r n a i r s t r e a m a b o u t 12 c m a b o v e t h e c o i l i n t h e s a m p l e i n s e r t . D u e t o t h e c o n s t r u c t i o n o f t h e l e a d i t w a s i m p o s s i b l e t o p l a c e t h e c o u p l e c l o s e r t o t h e c o i l s u r r o u n d i n g t h e s a m p l e . H o w e v e r , a t t h e c o n c l u s i o n o f t h e r u n s t h e t e m p e r a t u r e g r a d i e n t b e t w e e n s a m p l e a n d t h e r m o c o u p l e w a s d e t e r m i n e d b y r u n n i n g a s e c o n d c o u p l e t h r o u g h t h e a i r i n t a k e a n d i n t o a s e a l e d b u t e m p t y s a m p l e t u b e . T h e p r e s e n c e o f t h e c o u p l e i n t h e a i r i n t a k e p a s s a g e a f f e c t e d t h e r a t e o f f l o w . U n f o r t u n a t e l y , a s w i l l b e n o t e d b e l o w i t w a s n o t f e a s i b l e t o p u t a p r e s s u r e g u a g e i n t h e s y s t e m a n d w h i l e i t w a s a t t e m p t e d t o m a i n t a i n e q u i v a l e n t f l o w r a t e s , t h e r a t e s m a y h a v e b e e n d i f f e r e n t . C o n s t a n c y o f t e m p e r a t u r e w h e n t a k i n g s p e c t r a w a s c h e c k e d b y g r a p h i c a l r e c o r d i n g . + o T e m p e r a t u r e s r e m a i n e d c o n s t a n t w i t h i n - 0 . 5 C f o r t h e , , r u n s r e c o r d e d . T h e r e p o r t e d t e m p e r a t u r e s a r e t h e a v e r a g e o f r e a d i n g s t a k e n o n a p r e c i s i o n p o t e n t i o m e t e r a t t h e b e g i n n i n g a n d e n d o f t h e s e t o f s p e c t r a a t e a c h t e m p e r a t u r e . T h e e l e c t r i c a l h e a t e r w a s c o n t r o l l e d b y a y a r i a c p l u g g e d i n t o a c o n s t a n t v o l t a g e t r a n s f o r m e r . U s i n g a n e e d l e v a l v e a n d p r e s s u r e g u a g e i t w a s i m p o s s i b l e t o g e t s u f f i c i e n t a i r f l o w t o g i v e a d e q u a t e h e a t i n g a n d i t w a s n e c e s s a r y t o t a k e t h e a i r d i r e c t l y ( w i t h f i l t e r i n g ) f r o m t h e l i n e s . F l u c t u a t i o n s i n t e m p e r a t u r e g r e a t e r t h a n t h o s e n o t e d a b o v e w e r e o b s e r v e d d u e t o a i r p r e s s u r e c h a n g e b u t i n s u c h c a s e s t h e s y s t e m w a s p e r m i t t e d t o r e - e s t a b l i s h e q u i l i b r i u m b e f o r e s p e c t r a w e r e r e c o r d e d . - 57 -CHAPTER VI RESULTS A. FATTY ACIDS The o r i g i n a l i n t e n t i o n i n undertaking t h i s i n f r a r e d i n v e s t i g a t i o n of some s e l e c t e d f a t t y a c i d s had been to c a r r y out f a i r l y p r e c i s e q u a n t i t a t i v e measurements. However, a number of u n s u c c e s s f u l attempts showed t h a t accurate c o n t r o l of o r i e n t a t i o n , sample t h i c k n e s s , r e f l e c t i v i t y and s c a t t e r i n g i n s o l i d f i l m s would be very d i f f i c u l t . This a p p l i e s a l s o but to a s l i g h t l y l e s s e r extent to samples run i n KBr p e l l e t s . As noted e a r l i e r , sample t h i c k n e s s was chosen to give e s s e n t i a l l y equal true and apparent e x t i n c t i o n c o e f f i c i e n t s . However, due to other f a c t o r s , i n c l u d i n g n o n - p a r a l l e l r a d i a t i o n and f i n i t e s l i t w idth as w e l l as those above, the true and apparent c o e f f i c i e n t s may s t i l l d i f f e r by some 20%. Indeed, i t has been s t a t e d (53) t h a t the c o n s i d e r a b l e labour i n v o l v e d i n e v a l u a t i n g true e x t i n c t i o n c o e f f i c i e n t s and i n t e g r a t e d a b s o r p t i o n i n t e n s i t i e s f o r s o l i d samples i s s c a r c e l y j u s t i f i e d by the r e s u l t s obtained. F o r t u n a t e l y , however, i n the o p t i c a l d e n s i t y range from 0.2 to 0.7 the true and apparent i n t e g r a t e d a b s o r p t i o n i n t e n s i t i e s may d i f f e r by only about $% and apparent i n t e n s i t y can be used q u i t e s a t i s f a c t o r i l y . No attempt t h e r e f o r e was made i n - 5 8 -t h i s work to o b t a i n true v a l u e s but comparisons were made between apparent v a l u e s . I f care i s taken reasonably good r e l a t i v e values may be obtained f o r s o l i d phase i n f r a r e d s p e c t r a . P r e l i m i n a r y s t u d i e s of the i n f r a r e d spectrum of s t e a r i c a c i d from lj.000 cm\" 1 to 6 0 0 cm\" 1 showed (F i g u r e s IX and X) a g e n e r a l broadening and l o s s of d e f i n i t i o n of the bands, p a r t i c u l a r l y the CH 2 bands, on h e a t i n g . In the f u l l spectrum the 7 2 7 , 7 2 0 cm\" 1 doublet i s b a r e l y r e s o l v e d and r a p i d l y l o s e s i t s d e f i n i t i o n as the temperature i n c r e a s e s . Appendix I c o n t a i n s r e p r o d u c t i o n s of r e p r e s e n t a t i v e expanded s p e c t r a o f a l l f o u r a c i d s s t u d i e d . The expanded s p e c t r a were t r a n s f e r r e d from the l o g a r i t h m i c g r i d on the c h a r t paper to a l i n e a r p l o t of o p t i c a l d e n s i t y a g a i n s t wave number. The behaviour of the s p e c t r a w i t h changing temperature i s shown i n F i g u r e s XI, XII, X I I I , XIV f o r samples run as c r y s t a l l i n e f i l m s between s a l t p l a t e s . The behaviour when samples were run i n KBr p e l l e t s was s i m i l a r . The t o t a l band between 7 5 0 and 7 0 0 cm 1 was r e s o l v e d Into i t s component bands by u s i n g the a b s o r p t i o n i n the v i c i n i t y of 7 5 0 cm\" 1 to f i x the base l i n e . P r e l i m i n a r y s p e c t r a had i n d i c a t e d that f o r a l l the a c i d s , the a b s o r p t i o n at 7 5 0 cm\" 1 was a convenient l o c a l minimum.(it was i n f a c t the absolute minimum f o r the e n t i r e range L L O O O to 6 0 0 cm\" 1) and that the minimum TO FOLLOW PAGE 58 TO FOLLOW PAGE 58 FIGURE XIII, MYRISTIC ACID EXPANDED SPECTRA M.PT. 5 4 . 3 - 5 4 . 5 \u00b0 C 7 4 0 I 7 3 0 -o 7 4 . 8 t A 74BN> 5 3 4 A 455 THE S P E C T R A MARKEO A EXHIBIT ANOMALOUS BEHAVIOUR. THE 727 C M - ' BAND DOES NOT DtS APPEAR, BUT B E C O M E S THE PRINCIPAL PEAK ABOVE THE TRANSITION RANGE. THE SPECTRUM MARKED \" N \" INDICATES THE EXPECTED \"NORMAL\" BEHAVIOUR ( OBSERVED FOR OTHER MYRISTIC ACID SAMPLES ) OF THE CORRESPONDING TEMPERATURE \"ANOMALOUS\" SPECTRUM. H O R r 5 o CD - 3 0 . I \u00b0 C 72 0 71 0 i _ 7 0 0 TO FOLLOW PAGE 58 - 59 -r e m a i n e d e s s e n t i a l l y c o n s t a n t ( a b o u t -0.01 o p t i c a l d e n s i t y c h a n g e ) . R e s o l u t i o n o f t h e b a n d s w a s m a d e u s i n g t h i s b a s e l i n e a c c o r d i n g t o t h e f o l l o w i n g c r i t e r i a (8): ( i ) t h a t t h e e x t i n c t i o n c o e f f i c i e n t s o f t h e b a n d s w e r e a d d i t i v e , ( i i ) t h a t t h e b a n d s w e r e s y m m e t r i c a l a b o u t t h e i r m a x i m a , ( i i i ) t h a t t h e b a n d s p o s s e s s e d n o a p p r e c i a b l e p o r t i o n o f t h e i r a r e a s i n l o n g t a i l s e x t e n d i n g f a r f r o m t h e i r m a x i m a , a n d ( i v ) t h a t t h e t r a n s m i s s i o n l o s s e s d u e t o s c a t t e r i n g c o u l d b e i n t e r p o l a t e d f r o m t r a n s m i s s i o n m e a s u r e m e n t s o n e i t h e r s i d e o f t h e b a n d w h e r e n o a b s o r b a n c e w a s a s s u m e d t o o c c u r . T h e r e s o l u t i o n o f s p e c t r a i n t h e v i c i n i t y o f 35\u00b0C i s i n d i c a t e d i n F i g u r e s X V , X V I , X V I I , X V I I I . T w o p r o m i n e n t p e a k s a n d a t h i r d p e a k w h i c h s o m e t i m e s a p p e a r s o n l y a s a s h o u l d e r w e r e r e c o g n i z a b l e i n t h e 750 t o 700 c m 1 r e g i o n . T h e p e a k s w e r e r e s o l v e d a c c o r d i n g t o t h e p r o c e d u r e o u t l i n e d a b o v e a n d t h e i r v a r i a t i o n i n i n t e g r a t e d i n t e n s i t y w i t h t e m p e r a t u r e p l o t t e d i n F i g u r e s X I X , X X , X X I , X X I I . T h e i n t e n s i t i e s g i v e n a r e i n a r b i t r a r y u n i t s u n r e l a t e d f r o m o n e a c i d t o t h e n e x t . A c c u r a t e r e s o l u t i o n w a s e x t r e m e l y d i f f i c u l t a n d e r r o r s i n i n t e g r a t e d i n t e n s i t i e s o f 1$% m a y e a s i l y b e e n c o u n t e r e d . B e c a u s e o f t h e d i f f i c u l t y i n r e s o l u t i o n , i t w a s d e c i d e d TO FOLLOW PAGE 59 \"0.05 \u2014 p ~ -0.10 \\\\ \\ \/ \/ \\ \\ V \/ -015 \\ \\ \/ \\ \/ \\ x y \\ \/ \\ n \\ \/ \\ \\ \\ \/ \\ \\ \\ y \\ \\ \\ A \\ \\ v-\/\/ -0.20 g m -0.25 \u00a7 H -< FIGURE XVIII -0.30 LAURIC ACID RESOLUTION AT 33.6\u00b0C -0.35 FREQUENCY CM\" 1 750 740 730 i 720 i 710 i 700 FIGURE XIX STEARIC ACID. TEMPERATURE DEPENDENCE OF THE APPARENT INTEGRATED ABSORPTION INTENSITIES OF T H E RESOLVED BANDS O \u00a9 B STARTING TEMPERATURE \u2022 , \u2022 DECREASING TEMPERATURE O INCREASING TEMPERATURE a 80 90 ^ \u2014 o <--600 ISO I m 2 -500 8 -400 l o -300 m z CO -200 -100 C 2 H CO 720 C M - 1 O BAND HIGH FREQUENCY BAND (740.5 C M - ' ) 'O O O o 10 i_ TEMPERATURE \u00b0C 40 FIGURE XX PALMITIC ACID. TEMPERATURE DEPENDENCE OF THE APPARENT INTEGRATED ABSORPTION INTENSITIES OF THE RESOLVED BANDS O \u00a9 > O STARTING TEMPERATURE %j \u2022 DECREASING TEMPERATURE O ) Q INCREASING TEMPERATURE 3 60OH m 500 > CD CO O 3 -400 CO -i \u2022< 30 Q_ z > X CO -20C\u00a7 c z 7 2 0 C M H e - \u00a9 - 7 2 7 C M \" FIGURE XXI MYRISTIC ACID (\"kNOMALOUS\") TEMPERATURE DEPENDENCE OF THE APPARENT INTEGRATED ABSORPTION INTENSITIES OF THE RESOLVED BANDS <$,fy STARTING TEMPERATURE # 9 DECREASING TEMPERATURE O \u00a9 INCREASING TEMPERATURE NOTES'-(I) FOR A NORMALLY BEHAVING MYRISTIC ACID SAMPLE, THE 727 CM - 1 BAND IS NOT FOUND IN THE TRANSITION OR MELT REGIONS AS IT IS IN THIS PARTICULAR ANOMALOUSLY BEHAVING SAMPLE. (II) THE PARALLEL DISPLACEMENTS OF THE COOLING PORTIONS OF THE CURVES ARE DUE TO CHANGES IN THE ORIENTATIONS IN THE POLYCRYSTALLINE FILM AFTER REFREEZING FROM THE MELT. O IOQ_ \u2022 10 i 0 10 TEMPERATURE \u00b0C 20 30 4 0 \u2014I 1 1 \u2014 50 i 60 i 70 i _ rn 8 TO FOLLOW PA6E 59 UJ Z u o o UJ a: CL < 2 O o CM APPARENT INTEGRATED O O m I ABSORPTION O O c Cfl Cfl O SET ONE \u2022 SET TWO hO.IO L 0 . 0 5 ^ H - \/ , . FOR WATER AT 25\u00b0C UNDER THE SAME CONDITIONS AS SET ONE IS 0.02 GAUSS-iono 120 _J 140 i 160 i 180 TEMPERATURE 200 FIGURE XXIII SODIUM STEARATE LINE WIDTHS 2 4 0 2 6 0 o o 280 o 3 0 0 i TO FOLLOW PAGE 67 FIGURE XXIV SODIUM STEARATE SECOND MOMENTS CO rn o o -0.01 o o r i \u2022aooi o ro O SET ONE \u2022 SET TWO A H f FOR WATER AT 25\u00b0C UNDER THE SAME CONDITIONS AS SET ONE IS - I O - * G A U S S 2 O P 77 120 QOQQI 140 160 _ J TEMPERATURE \u00b0C 180 200 220 240 260 \u2014I 1 l I I 2 8 0 | - 68 -The o r i g i n a l i n t e n t i o n i n the i n v e s t i g a t i o n of sodium s t e a r a t e had been to p l o t d e r i v a t i v e curves from the a b s o r p t i o n curves and hence determine the l i n e widths between maximum and minimum s l o p e . However, f o r the s p e c t r a between 1 2 0 and 23f>\u00b0C the l i n e widths were e s s e n t i a l l y constant being between 0 . 0 6 and 0 . 0 9 gauss. Above 235\u00b0C the l i n e width narrowed to about 0 . 0 1 or 0 . 0 2 gauss but could be measured even l e s s a c c u r a t e l y than at lower temperatures. The constancy of the l i n e width between maximum and minimum slope i n d i c a t e s that the a b s o r p t i o n l i n e c o n s i s t s of a comparatively narrow spike superimposed on a broad p e d e s t a l . T h i s i s most apparent i n the s p e c t r a taken at the f a s t e r sweep r a t e s i n c e i n the slower sweep r a t e s p e c t r a the spike i s p a r t i a l l y masked by the wide s i g n a l . The l i n e width at the same temperature i s the same f o r both s e t s of course. While the narrow spike d i d not change w i t h temperature, the wings or p e d e s t a l d i d and the l i n e width AHX at one-half maximum amplitude g i v e s a d e s c r i p t i o n of 2 the behaviour of the s i g n a l . Below 120\u00b0C the l i n e was too broad to be found on the spectrometer's o s c i l l o s c o p e and could not be recorded c o n v e n i e n t l y as an a b s o r p t i o n curve. However, at 120\u00b0C the s i g n a l i s narrow enough to be recorded on the h i g h r e s o l u t i o n spectrometer. At t h i s temperature the wings are very prominent but they d i m i n i s h s t e a d i l y w i t h i n c r e a s i n g temperature u n t i l 2 3 5\u00b0C Is reached. Between 2 3 5 and 237\u00b0C the wings disappear and the - 69 -a b s o r p t i o n band takes on a shape, l i n e width, and second moment comparable to that of a water sample the spectrum of which was taken i n the same f i e l d f o r comparison. The v a r i a t i o n of l i n e width w i t h temperature i s shown i n F i g u r e XXIII. The only t r a n s i t i o n s which are c l e a r l y i n d i c a t e d by the l i n e width-temperature curve are between 119 and 120\u00b0C and between 235 and 237\u00b0C In the former case the s i g n a l i s too broad to be measured c o n v e n i e n t l y by h i g h r e s o l u t i o n techniques and an obvious change i n l i n e width takes p l a c e at t h i s p o i n t even though l i n e width cannot be measured below the t r a n s i t i o n (Grant (12) g i v e s 2.8 gauss below the t r a n s i t i o n but p l a c e s the t r a n s i t i o n at between 113 and III4. C). In the l a t t e r case the l i n e width drops suddenly to a value comparable to t h a t f o r a l i q u i d but does t h i s w e l l before the m e l t i n g p o i n t (275~280\u00b0C) of the sample i s reached. The v a l u e s r e p o r t e d here are at the l i m i t o f the experimental accuracy and the s c a t t e r i n g of p o i n t s makes i t d i f f i c u l t to f i x the t r a n s i t i o n p o i n t s . Above 235>\u00b0C, where the s p e c t r a have a completely l i q u i d - l i k e c h a r a c t e r , the base l i n e s are b e t t e r than at lower temperatures, but the l i n e w i d t h i n such a l i q u i d - l i k e r e g i o n i s governed by the f i e l d inhomogeneity. That the v a l u e s g i v e n there are h i g h e r i n the second set of runs than the f i r s t i s b e l i e v e d to be due to the presence of a l e s s homogeneous magnetic f i e l d i n the former case. The second moments were computed from the a b s o r p t i o n s i g n a l by n u m e r i c a l i n t e g r a t i o n . For numerical - 7 0 -i n t e g r a t i o n of the a b s o r p t i o n l i n e , e q uation (I4.9) becomes 2 2 a AH = ( s c a l e f a c t o r ) X (52) 2 For c a l c u l a t i o n the base l i n e i s taken as the x - a x i s , which i s d i v i d e d i n t o equal d i v i s i o n s , the y value f o r each d i v i s i o n measured, a s c a l e f a c t o r i n .gauss\/division,* computed from the sweep r a t e c a l i b r a t i o n , and the sums computed. In set one base l i n e d i f f i c u l t i e s made i t necessary to average the a b s o r p t i o n l i n e s by superimposing them on each other and drawing an average curve f o r each temperature. T h i s was the only p o s s i b l e way to o b t a i n v a l u e s f o r t h a t s e t . In set two the same procedure was f o l l o w e d but i t was found i n checking the second moment obtained from the averaged curve a g a i n s t moments obtained from i n d i v i d u a l curves, that the average curve's second moment was very s e n s i t i v e to the manner i n which the wings were drawn i n . Consequently moments were computed from the i n d i v i d u a l s p e c t r a i n set two. U n f o r t u n a t e l y due to v a r i a t i o n s i n wing area, i n d i v i d u a l second moments at the same temperature could d i f f e r by l a r g e amounts ( 1 0 0 $ i n an extreme c a s e ) . In set one there f r e q u e n t l y was, as may be seen from Appendix I I , the a d d i t i o n a l c o m p l i c a t i o n of a h i g h noise l e v e l i n the wings. The v a r i a b l e wings s e r i o u s l y a f f e c t the accuracy of the second moment c a l c u l a t i o n s . The p o i n t of one-half maximum amplitude i s w e l l above the wings and due to the comparative narrowness of the spike the l i n e w i d t h i s s r e l a t i v e l y u n a f f e c t e d ( d i f f e r e n c e s between i n d i v i d u a l s p e c t r a - 71 -at the same temperature were of the order of 10%) by d i f f e r i n g base l i n e s . The second moments, nonetheless, proved to be the more u s e f u l of the two measurements. In s p i t e of t h e i r seeming i n a c c u r a c y , the second moment c a l c u l a t i o n s gave r e s u l t s which, as w i l l be seen l a t e r , were r e a d i l y i n t e r p r e t a b l e . The second moment curve (Figure XXIV) i n i t s lower temperature r e g i o n agrees reasonably w e l l w i t h the values obtained by Grant (12) , o between l i q . and 130 G. However, the t r a n s i t i o n r e p o r t e d by Grant as o c c u r r i n g between 113 and llq\u00b0C appears from o t h i s work to take place between 119 and 120 C. Grant determined the value of the second moment j u s t below the 2 t r a n s i t i o n as 6.7 gauss . This would be c o n s i s t e n t w i t h o the low, too broad to be measured s i g n a l found below 120 G i n the present work.- No abrupt changes i n second moment ,o can be seen between 120 and 235 G. The second moment decreases g r a d u a l l y but remains, w i t h i n experimental e r r o r , 2 o at about 0.1 gauss . Between 235 and;.237 0 a sudden change takes p l a c e . The second moment decreases to a value of the order of 10 ^ g a u s s 2 comparable to the value found f o r a water sample at room temperature i n the same f i e l d . - 72 -CHAPTER VII DISCUSSION A. FATTY ACIDS The 720 cm 1 doublet has been observed i n the i n f r a r e d spectrum' of very many although not a l l compounds c o n t a i n i n g f o u r or more consecutive s t r a i g h t c h a i n methylene groups. That the band was due to the CH 2 r o c k i n g v i b r a t i o n was e s t a b l i s h e d by many i n v e s t i g a t o r s only some of whom (59) (60) (62) (83 ) (8I4.) are mentioned here. Although the intense 720. cm 1 band was rec o g n i z e d as only the t e r m i n a l band of a long s e r i e s extending from 720 to about 1050 cm 1 (83)(84) most work has been concerned w i t h i t . Snyder (6I4.) has d e r i v e d an e x p r e s s i o n - (6\/-4\/ -Wu* + lt>.7Xu\u00bb\u00a3 - + cQScoSfylo1 -which g i v e s , to an e x c e l l e n t approximation, the frequency i n cm\" 1 of the methylene r o c k i n g bands i n unperturbed, f u l l y extended n - p a r a f f i n s . The e x p r e s s i o n depends on a s i n g l e parameter 0k,ra the phase d i f f e r e n c e between adjacent o s c i l l a t o r s (the CH 2 groups). v.-1.1,3, m K = oii ior- Arv infmr\u00ab and s o l v i n g f o r x one obt a i n s ( l 7 J 7 c \/ l 7 2 0 c , ) o ^3) where j> = I W O j \/ l 72,Oc In e x p r e s s i o n (58) the r a t i o (1j2f\/1j2o\\ m a J be r e a d i l y obtained from a p l o t of the r a t i o a g a i n s t temperature. When the sample i s completely c r y s t a l l i n e x - l and from equation ( S 7) l ^ ^ ) , = U \u00bb ( I ^ \/ I ^ . P l o t s of (I \/ I ) a g a i n s t temperature (not shown here) i n d i c a t e t h at the slope of the curve Is zero at the lower temperatures s t u d i e d i n t h i s work. I f the constancy of the r a t i o may be taken to mean that the sample i s completely c r y s t a l l i n e , then (I \/ l ) may be s a f e l y evaluated J ' 727c 720c o some 60 to 90C below the m e l t i n g p o i n t . T h i s cannot be s t a t e d w i t h c e r t a i n t y from i n f r a r e d data, but i t seems a reasonable assumption. Snyder (5) has obtained an e x p r e s s i o n f o r the r e l a t i v e i n t e n s i t i e s of the components i n the CH^ r o c k i n g doublets i n c r y s t a l l i n e p a r a f f i n s . When a p p l i e d to the 720-727 cm 1 doublet the e x p r e s s i o n g i v e s Ilil - (s*\\) - 79 -where \u00a9 i s the angle which the plane of the hydrocarbon c h a i n makes w i t h the a-axis of the c e l l . Hence i f 0 i s l e s s than 1+5\u00b0 at low temperatures, the I n t e n s i t y r a t i o w i l l be l e s s than one even though the sample i s completely c r y s t a l l i n e . E q u a t i o n (59) g i v e s values of e between 37 and 1+1+\u00b0 f o r the f o u r a c i d s i n v e s t i g a t e d . These values are i n good agreement w i t h the value of 1+2-5\u00b0 found by Smith (90) f o r orthorhombic n-C^H^g and that of 3 8 \u00b0 computed f o r C-form l a u r i c a c i d from Vand's data ( 2 7 ) . This suggests that the values of the (I \/ l ) r a t i o s 727c 720c o used i n the c a l c u l a t i o n of the c r y s t a l l i n i t y curves shown i n F i g u r e XXV, are probably f a i r l y c o r r e c t . The value of p can only be estimated s i n c e i t i s dependent on measurements above the m e l t i n g p o i n t which may be of d o u b t f u l accuracy. In the melt r e g i o n not only i s r e s o l u t i o n d i f f i c u l t but a l s o e r r o r s due to d i f f e r e n t s c a t t e r i n g and r e f l e c t i v i t y from t h a t below the m e l t i n g p o i n t may be encountered. Above the m e l t i n g p o i n t x=0 a n d I 7 2 0 a = I 7 2 0 O I > ' a S \u00b1 l 1 S t h e n c a l l e d > I 7 2 1 * A * l 0 W temperatures where x=l, i t i s seen t h a t I Y 2 0 C = 1 7 2 0 \" E v a l u a t i o n of the r a t i o suggested t h a t p=-| was a reasonable estimate. A check on the value of p may be obtained by examining the behaviour of the 720 cm 1 component.- By r e a r r a n g i n g e q u a t i o n (56) to give \\ - 8 0 -one sees t h a t i f p >1, I 7 2 Q a > I J 2 Q C a n d 1J20 l n c r e a s e s as x decreases. I f P =1, I \u201e =1 and I remains 7 2 0 a 7 2 0 c 7 2 0 constant. I f P<1, I < I . and I decreases as 7 2 0 a 7 2 0 c . 7 2 0 x decreases. I t i s the l a s t case which a p p l i e s f o r the f a t t y acid's thus c o n f i r m i n g t h a t ? i s of the c o r r e c t magnitude. In F i g u r e XXV. the c r y s t a l l i n i t y x i s p l o t t e d f o r each of the f o u r f a t t y a c i d s as a f u n c t i o n of T r.T the temperature i n t e r v a l below the m e l t i n g p o i n t T . W e l l below the m e l t i n g p o i n t the a c i d s show what might be considered a s u r p r i s i n g l a c k of c r y s t a l l i n i t y . The l a c k of c r y s t a l l i n i t y i s so great t h a t one wonders i f x does indeed r e p r e s e n t t h a t q u a n t i t y . Perhaps estimate of order might be a b e t t e r d e s i g n a t i o n f o r x. Comparison of these curves w i t h s i m i l a r curves d e r i v e d from n.m.r. data presented i n Barr, Grant and D u n e l l (11) shows t h a t while q u a l i t a t i v e behaviour i s the same, w i t h the same r e l a t i v e order of c r y s t a l l i n i t y being maintained, the i n f r a r e d curves i n d i c a t e much g r e a t e r n o n - e r y s t a l l i n i t y f o r the samples. This might be a t t r i b u t e d to e r r o r s i n e v a l u a t i n g j> but even a value of $ - Z , (not shown h e r e ) , which cannot p o s s i b l y be j u s t i f i e d by the experimental r e s u l t s , while i t g i v e s a reasonably appearing c p y s t a l l i n i t y curve s t i l l shows l e s s c r y s t a l l i n i t y than t h a t i n d i c a t e d by the n.m.r. curves. Probably the i n f r a r e d r e s u l t s are f a i r l y good, at l e a s t to the extent of being a good q u a l i t a t i v e r e p r e s e n t a t i o n , and the d i s c r e p a n c y may perhaps - 81 -be e x p l a i n e d by a d i f f e r e n c e i n the p i c t u r e s \"seen\" by i n f r a r e d and n.m.r. Since one would expect n.m.r. to be more s e n s i t i v e to m o l e c u l a r r e o r i e n t a t i o n than i s i n f r a r e d spectroscopy, i t i s s u r p r i s i n g , u n l e s s the r e s u l t s here are g r o s s l y i n e r r o r , t h a t the i n f r a r e d data i n d i c a t e a h i g h e r degree of d i s o r d e r than the n.m.r. This may p o s s i b l y be e x p l a i n e d by n o t i n g that n.m.r. c a l c u l a t i o n s show only those molecules which are r e o r i e n t i n g . Perhaps as i n form A of potassium caprate ( 3 1 ) , there i s not a p e r f e c t l y r e p e a t i n g c r y s t a l p a t t e r n i n the f a t t y a c i d s and a p a r t i a l l y random s u c c e s s i o n of c h a i n i n c l i n a t i o n s and o r i e n t a t i o n s from l a y e r to l a y e r may e x i s t . Vand ( 2 7 ) has found t h a t the hydrocarbon c h a i n i n C-form l a u r i c a c i d i s not f u l l y extended i n a z i g z a g but i s bent. This may a f f e c t the phase r e l a t i o n s h i p s between the o s c i l l a t o r s (methylene groups) In the c h a i n and r e s u l t i n a p a r t l y amorphous c h a r a c t e r f o r the i n f r a r e d s p e c t r a . I f some chains are i n d i s a r r a y or even s l i g h t l y t w i s t e d but s t i l l r i g i d l y f i x e d , the i n f r a r e d s p e c t r a , which f o r the 7 2 0 - 7 2 7 cm 1 doublet are dependent on ordered c r y s t a l i n t e r a c t i o n s , could i n d i c a t e a f a i r l y h i g h amorphous nature at a comparatively low temperature. The n.m.r. s p e c t r a , however, would not show t h i s s i n c e the molecules although i n some d i s o r d e r (perhaps s l i g h t l y t w i s t e d or not f u l l y extended) would s t i l l not be r e o r i e n t i n g . The c r y s t a l l i n i t y curves i n F i g u r e XXV:. show a - 82 -s t e a d i l y i n c r e a s i n g d i s o r d e r from q u i t e f a r below the m e l t i n g p o i n t f o r s t e a r i c and m y r i s t i c a c i d s as the temperature i s i n c r e a s e d . P a l m i t i c and l a u r i c a c i d s show the same behaviour but d i s o r d e r does not become pronounced u n t i l h i g h e r temperatures are reached. I t appears that an a l t e r n a t i o n of order may e x i s t among the f o u r f a t t y a c i d s s t u d i e d here. L a u r i c (O^) and p a l m i t i c (C-^) a c i d s f a l l i n the same r e g i o n i n F i g u r e XXV' and behave s i m i l a r l y w i t h changing temperature. Normally behaving m y r i s t i c a c i d (C-^) and s t e a r i c a c i d (C^g) a l s o f a l l together, but i n a d i f f e r e n t r e g i o n from the other two a c i d s , and a l s o behave s i m i l a r l y to each other w i t h changing temperature. Since th.6 normal m y r i s t i c sample was In a p r e l i m i n a r y s et which was not taken below 30\u00b0G i t s low temperature values were obtained by e x t r a p o l a t i o n and i t consequently i s the l e a s t r e l i a b l e of the curves shown. I t i s f e l t , however, because of the g e n e r a l s i m i l a r i t y of the behaviour of i t s s p e c t r a to that of s t e a r i c a c i d , that i t s p o s i t i o n near the l a t t e r a c i d i n d i c a t e s that the curve l i e s i n the c o r r e c t g e n e r a l r e g i o n . I t probably should i n d i c a t e , however, t h a t m y r i s t i c a c i d i s more c r y s t a l l i n e than s t e a r i c a c i d r a t h e r than the r e v e r s e . I t i s unfortunate that the run on m y r i s t i c a c i d which i n c l u d e d low temperatures was a sample t h a t behaved anomalously. The comparatively h i g h c r y s t a l l i n i t y e x h i b i t e d by t h i s sample may be due to the p o s s i b i l i t y expressed above t h a t a fundamental r o c k i n g mode, which does not v a n i s h i n i n t e n s i t y above the m e l t i n g p o i n t , - 83 -was c o n t r i b u t i n g to the apparent 727 cm\"\"1 band a r i s i n g from i n t e r m o l e c u l a r p e r t u r b a t i o n s . P o s s i b l y the c o r r e c t m y r i s t i c a c i d curve i s between the two showing f a i r l y much more c r y s t a l l i n i t y than the normal curve, as i s suggested by the anomalous curve, but having a shape s i m i l a r to that of the normal curve. The g r a d u a l l y i n c r e a s i n g d i s o r d e r e x h i b i t e d by the f a t t y a c i d s as the temperature i s i n c r e a s e d may be termed the approach to or perhaps beginning of p r e m e l t i n g . There i s some doubt as to how a c c u r a t e l y the c r y s t a l l i n i t y curves i n F i g u r e XXV' r e p r e s e n t the true c o n d i t i o n s . There i s no doubt, however, about the disappearance of c r y s t a l l i n i t y i n the t r a n s i t i o n r e g i o n s l i g h t l y below the m e l t i n g p o i n t . The curves i n F i g u r e XXV and the t r a n s i t i o n range i n Table VII show t h a t c r y s t a l l i n i t y f i n a l l y d i sappears f a i r l y a b r u p t l y about 2C\u00b0 below the m e l t i n g p o i n t i n s t e a r i c a c i d , about l . ^ C 0 below i n both normally and anomalously behaving m y r i s t i c a c i d and about 1C\u00b0 below i n p a l m i t i c and l a u r i c a c i d s . Except f o r l a u r i c a c i d , these temperatures correspond w i t h those, l i s t e d i n Table V I I I , at which the c r y s t a l s appeared to become somewhat p l a s t i c . In a d d i t i o n a l t h o u g h i n f r a r e d and n.m.r. techniques i n d i c a t e d d i f f e r e n t degrees of c r y s t a l l i n i t y over the range s t u d i e d , they showed t h a t the a c t u a l temperatures at which c r y s t a l l i n i t y vanished were the same by both methods (11). The i n f r a r e d s p e c t r a take on a completely l i q u i d - l i k e appearance (as do the n.m.r. s p e c t r a ) i n the t r a n s i t i o n - 8k ~ r e g i o n but seem to decrease i n i n t e n s i t y a s l i g h t amount when the r e s p e c t i v e m e l t i n g p o i n t s are reached. .This e x h i b i t i o n j u s t below the m e l t i n g p o i n t of an abrupt d i s c o n t i n u i t y i n the c r y s t a l l i n i t y which c l e a r l y foreshadows a c t u a l m e l t i n g e x a c t l y f i t s the d e f i n i t i o n o f p r e m e l t i n g . U n t i l the f a t t y a c i d s ' t r a n s i t i o n temperatures are reached the i n f r a r e d r e s u l t s merely show a g r a d u a l l y i n c r e a s i n g d i s o r d e r . Probably, as suggested by Chapman f o r sodium soaps ( l i ) , as the temperature i s i n c r e a s e d the i n c r e a s i n g l a c k of r e s o l u t i o n between the band components i s due to the hydrocarbon chains beginning to f l e x and t w i s t . T h i s w i l l produce some r o t a t i o n a l isomerism w i t h each isomer having i t s own s l i g h t l y d i f f e r e n t frequency i n the r e g i o n w i t h a r e s u l t a n t smearing out of the spectrum. That i s , as the chains t w i s t and f l e x , i t w i l l no longer be p o s s i b l e to. have a l l o s c i l l a t o r s e x a c t l y in-phase and out-of-phase. Band I n t e n s i t y w i l l d i m i n i s h sin c e there w i l l be fewer o s c i l l a t o r s at any one frequency and the bands w i l l widen out s i n c e more v i b r a t i o n a l f r e q u e n c i e s w i l l a r i s e i n the r e g i o n due to the i n c r e a s e d number of phase r e l a t i o n s h i p s between o s c i l l a t o r s . Grant ( 1 2 ) has p o i n t e d out that l a t t i c e d e f e c t s due to d i s l o c a t i o n s and i m p u r i t i e s i n the c r y s t a l might allow the hydrocarbon chains to r o t a t e about t h e i r long axes and to f l e x and whip about while remaining i n t h e i r l a t t i c e p o s i t i o n s . Then as the temperature rose the zones of - 85 -motion and d i s o r d e r would grow at the expense of the surrounding, ordered c r y s t a l s t r u c t u r e u n t i l j u s t below the m e l t i n g p o i n t the s t r u c t u r e was completely amorphous. The m e l t i n g p o i n t then would correspond to the breakdown of the amorphous s t r u c t u r e . A t r a n s i t i o n below the m e l t i n g p o i n t has not been r e p o r t e d i n the f a t t y a c i d s by p r e v i o u s i n v e s t i g a t o r s (8)(56)(91) except f o r one a c i d (91). T h i s may p o s s i b l y be due to the c l o s e n e s s of the t r a n s i t i o n p o i n t to the m e l t i n g p o i n t and the f a c t t h at i n unexpanded s p e c t r a (56)(91) the behaviour of the doublet components i s d i f f i c u l t to observe. The one case i n which a t r a n s i t i o n was found was i n c a p r i c a c i d where C o r i s h and Chapman (91) r e p o r t e d t h a t , on c o o l i n g the sample the s i n g l e 720 cm\" 1 band s p l i t i n t o a doublet somewhere between 21+ and -78\u00b0C. Since t h i s was i n unexpanded s p e c t r a i t i s very l i k e l y t h a t i n expanded s p e c t r a the doublet could be d i s t i n g u i s h e d c o n s i d e r a b l y c l o s e r to the a c i d ' s m e l t i n g o p o i n t at 31.5 C. C o r i s h and Chapman suggested that the c a p r i c a c i d t r a n s i t i o n was analogous to t h a t observed (88) when l o n g - c h a i n hydrocarbons, e s t e r s and a l c o h o l s change from a h i g h e r temperature hexagonal form w i t h r o t a t i n g chains to a lower temperature. more s t a b l e orthorhombic form. As noted e a r l i e r the hexagonal form w i l l not show s p l i t t i n g , the orthorhombic form w i l l . I t seems p o s s i b l e then t h a t the t r a n s i t i o n i n the f a t t y a c i d s may be from an orthorhombic c h a i n packing - 86 -to a hexagonal c h a i n packing. In support o f t h i s , one may note t h a t H o l l a n d and N i e l s e n (62) have s t a t e d t h a t the hexagonal form i n p a r a f f i n s occurs only above a t r a n s i t i o n and c l o s e to the m e l t i n g p o i n t . Below the t r a n s i t i o n the form i s orthorhombic as w i t h the C-form f a t t y a c i d s . Above the t r a n s i t i o n , i n the hexagonal s u b c e l l , one may expect r o t a t i o n of the hydrocarbon chains about t h e i r long axes (92). Crowe and Smyth (93), however, suggested from d i e l e c t r i c measurements on the C-form of s t e a r i c a c i d t h a t there was no r o t a t i o n a l phase below the m e l t i n g p o i n t . T h i s o b s e r v a t i o n may again be due to ,the c l o s e n e s s o f the t r a n s i t i o n to the m e l t i n g p o i n t . The narrow component n.m.r. l i n e width found (11)(12) i n the a c i d s near the m e l t i n g p o i n t s suggests molecules i n r a p i d motion. F i n a l l y , f o r the somewhat analogous n - p a r a f f i n s , S t e i n (8)(63) r e l a t e d the i n f r a r e d t r a n s i t i o n w i t h the d i s c o n t i n u i t i e s observed by M u l l e r (95) i n the x-ray d i f f r a c t i o n p a t t e r n s . The d i s c o n t i n u i t i e s correspond to the X - p o i n t s o f the r e s p e c t i v e hydrocarbons. Above these p o i n t s there i s an onset of f r e e r o t a t i o n or randomness of o r i e n t a t i o n about the long axes of the molecules (96). From the experimental evidence i n t h i s work, i t appears that a change i n c r y s t a l s t r u c t u r e takes p l a c e f a i r l y a b r u p t l y j u s t below the m e l t i n g p o i n t s of the f a t t y -1 a c i d s when the 727 cm or c r y s t a l l i n e component of the doublet d i s a p p e a r s . The t r a n s i t i o n i s a n t i c i p a t e d by a gra d u a l decrease, over a long temperature range, of the - 8? -c r y s t a l l i n e band. The grad u a l decrease i n d i c a t e s an i n c r e a s i n g f l e x i n g and t w i s t i n g and the beginning o f r o t a t i o n of the methylene c h a i n p o r t i o n of the molecule. The growing d i s o r d e r may take p l a c e by a co o p e r a t i v e i n c r e a s e i n l a t t i c e d e f e c t s as noted above. That the f a t t y a c i d s have t r a n s i t i o n s much c l o s e r to the m e l t i n g p o i n t than i n the n - p a r a f f i n s (except f o r very long c h a i n p a r a f f i n s which w i l l e x h i b i t some amorphous nature) i s reasonable. I f one imagines the n - p a r a f f i n s as being r o u g h l y analogous to c y l i n d r i c a l rods, they may be expected to pack q u i t e r e g u l a r l y i n t o an ordered, c r y s t a l l i n e a r r a y and e x h i b i t the accompanying i n f r a r e d s p e c t r a . However, because the chains are h e l d together o n l y by Van der Waal's f o r c e s , i t i s reasonable to expect those f o r c e s to be s u f f i c i e n t l y weak to permit the n - p a r a f f i n s to e x h i b i t amorphous c h a r a c t e r some degrees below.the m e l t i n g p o i n t . While i t has been suggested e a r l i e r t h a t the chains o f ' f a t t y a c i d molecules may not be i n as r e g u l a r an a r r a y as i n the p a r a f f i n s , i t i s probable t h a t the i n t e r m o l e c u l a r a t t r a c t i o n s i n v o l v i n g the a c i d s ' c a r b o x y l groups c o n t r i b u t e to h o l d i n g the chains f a i r l y f i r m l y i n t h e i r somewhat d i s o r d e r e d a r r a y . Thus, although the chains may t w i s t and f l e x as the temperature i s i n c r e a s e d , the a t t r a c t i v e f o r c e s anchor the molecules and the t r a n s i t i o n i n d i c a t i n g . a very l a r g e degree of d i s o r d e r cannot take plac e u n t i l q u i t e near to the m e l t i n g p o i n t . At t h i s p o i n t o n e ' f e e l s that the s t e a d i l y i n c r e a s i n g d i s o r d e r culminates i n r a p i d , random - 8 8 -reorientation about the chain axes accompanied by the breakdown of the carboxyl layers. At such close.proximity to the melting point i t i s l i k e l y that the change i s not to an ordered c r y s t a l form (hexagonal has been suggested for other cases ( 6 2 ) ( 8 8 ) ) b u t to an amorphous form closely resembling the melt. In this region the carboxyl layers are being broken down, d i f f u s i o n i s probably beginning to occur, and the melting point merely corresponds to the f i n a l breakdown of the amorphous structure. This would appear to be substantiated by the closeness, almost i n d i s t i n g u i s h a b i i i t y , of the spectra i n the. t r a n s i t i o n region and i n the melt. The f i n a l picture then of the f a t t y acids studied i s that of'.a gradually increasing disorder which culminates i n a t r a n s i t i o n to a very amorphous form close to but below the melting point. Since the t r a n s i t i o n form behaves very s i m i l a r l y to the melt, i t may c l e a r l y be termed a premelting phenomenon with the f i n a l , s l i g h t breakdown of the amorphous form corresponding to actual melting. - 89 -B. SODIUM STEARATE Table IV l i s t s a number of h i g h temperature phase t r a n s i t i o n s which have been observed i n sodium s t e a r a t e . Some t r a n s i t i o n s are h i n t e d a t i n F i g u r e XXIII between the obvious t r a n s i t i o n s at 119 to 120\u00b0C and 235 to 237\u00b0C but these intermediate t r a n s i t i o n s are very i l l - d e f i n e d and r e q u i r e a l i v e l y i m a g i n a t i o n f o r t h e i r o b s e r v a t i o n . In a d d i t i o n , the l i n e shape i s changing i n t h i s r e g i o n and under such c o n d i t i o n s (97), l i n e w i d t h i s ' not a completely r e l i a b l e index to the nature of temperature phenomena. The second moment, which i s a r e l i a b l e index (98), shows (Figure XXIV) o n l y the s i n g l e t r a n s i t i o n s at each end of the range. At the 119 to 120\u00b0C t r a n s i t i o n there i s a change i n second moment from a value too l a r g e to be c o n v e n i e n t l y measured by h i g h r e s o l u t i o n to a value of the order of 0.1 to 0.5 gauss . Such a change s u r e l y suggests a t r a n s i t i o n from a f a i r l y c r y s t a l l i n e s t a t e to a s t a t e i n which some l i q u i d - l i k e c h a r a c t e r i s p r e s e n t . Below t h i s o . t r a n s i t i o n , which he p l a c e d at 113 to I l k C, Grant (12) has observed t h a t t w i s t i n g and r o t a t i o n occurs about the hydrocarbon chain s ' long axes. Above the t r a n s i t i o n the chains are b e l i e v e d to be completely f r e e to r o t a t e about t h e i r l o n g axes and very l i k e l y f r e e to f l a i l about as w e l l . He b e l i e v e d the i o n i c l a y e r s to be maintained however. - 9 0 -T h i s i s e x a c t l y the p i c t u r e o f a t r a n s i t i o n from a f a i r l y c r y s t a l l i n e phase to a phase w i t h l i q u i d - l i k e c h a r a c t e r as i s suggested below. The second moment determined from the present h i g h r e s o l u t i o n work remains n e a r l y constant between the two observed t r a n s i t i o n s i n the h i g h temperature r e g i o n . The intermediate phases observed by other methods but not by n.m.r. must then be s t r u c t u r a l l y s i m i l a r . The s l i g h t slope to the second moment curve i n d i c a t e s g r a d u a l l y i n c r e a s i n g motion but not sharp phase changes. I t has p r e v i o u s l y been suggested that the hydrocarbon chains possess c o n s i d e r a b l e l i q u i d - l i k e behaviour i n t h i s r e g i o n . A r a t h e r obl i q u e c o n f i r m a t i o n of t h i s i s g i v e n by the f a c t that a l l the second moments of set two are l a r g e r than those o f set one i n Figure XXIV. The g r e a t e r magnitude f o r set two values was a s c r i b e d to s l i g h t l y g r e a t e r f i e l d inhomogeneity i n t h a t case, a c o n d i t i o n which would a f f e c t the s p e c t r a of a l i q u i d - l i k e sample but not a s o l i d . There i s an abrupt t r a n s i t i o n between 235 and 237\u00b0C. Here the sample's second moment f a l l s from a value of the 2 order of 0 . 1 gauss , b e l i e v e d to i n d i c a t e a l i q u i d - l i k e - i i 2 c o n d i t i o n , to a value o f the order of 1 0 gauss . T h i s very s m a l l second moment was of the same order as that of a water sample i n the same f i e l d (but at room temperature). This very s m a l l l i q u i d type second moment must i n d i c a t e d i f f u s i o n of molecules through the sample O i l ) . At t h i s p o i n t the a t t r a c t i o n of the i o n i c l a y e r s must be overcome - 9 1 -and the sample takes on a behaviour, as f a r as n.m.r. i s concerned, i n d i s t i n g u i s h a b l e from the i s o t r o p i c melt. The f o l l o w i n g p i c t u r e of sodium s t e a r a t e i s obtained from the h i g h r e s o l u t i o n n.m.r. r e s u l t s . Below 120\u00b0C the soap i s probably e s s e n t i a l l y c r y s t a l l i n e . The subwaxy, waxy, superwaxy and subneat phases form, a s t r u c t u r a l l y s i m i l a r group e x h i b i t i n g l i q u i d - c r y s t a l l i n e p r o p e r t i e s . F i n a l l y the neat phase and the melt form a s t r u c t u r a l l y s i m i l a r group w i t h the p r o p e r t i e s of a l i q u i d . There i s some c o n f l i c t between the view expressed above and that obtained by some other methods. VoldJs (I4.7) heat of t r a n s i t i o n measurements show the l a r g e s t heat ( 5 1 8 0 cal\/mole) observed at any temperature f o r sodium s t e a r a t e i s that f o r the supercurd to subwaxy t r a n s i t i o n at about llk\u00b0C. This suggests that i t i s probably t h i s t r a n s i t i o n t h at marks the departure from mostly c r y s t a l l i n e p r o p e r t i e s . The subwaxy to waxy t r a n s i t i o n has a heat of t r a n s i t i o n o n l y about 20% l e s s than that of the p r e v i o u s t r a n s i t i o n but the sample does not show a change i n second moment at t h i s p o i n t i n . t h e h i g h r e s o l u t i o n r e s u l t s . Since the two t r a n s i t i o n s are only l\u00a3 to 20C\u00ae. apart there may perhaps be a g r a d u a l t r a n s i t i o n as suggested by the g r a d u a l f a l l o f f of l i n e width through the r e g i o n 120 to lk0\u00b0C (Figure X X I I I ) . While the second moments i n F i g u r e XXIV do not i n d i c a t e such'a f a l l o f f Grant's (12) second moment curve does show i t , but modulation broadening may be an i n f l u e n c e t h e r e . While thermodynamic evidence - 92 -p r o v i d e s some c o n f i r m a t i o n f o r the i n t e r p r e t a t i o n of the supercurd to subwaxy t r a n s i t i o n , i t p r o v i d e s none f o r the subneat to neat t r a n s i t i o n . The heat o f t r a n s i t i o n f o r t h i s change which i s observed by n.m.r. i s of v i r t u a l l y the same magnitude (about 1 6 0 0 cal\/mole) as that f o r the superwaxy to subneat t r a n s i t i o n which i s not observed by n.m.r. However, the waxy to superwaxy t r a n s i t i o n i s not observed at a l l by Void f o r sodium s t e a r a t e and p o s s i b l y c a l o r i m e t r i c measurements may not provide a completely accurate estimate of the magnitude of t r a n s i t i o n s t a k i n g p l a c e i n t h i s s t r u c t u r a l l y complicated r e g i o n . Void's work shows t h a t sodium p a l m i t a t e and s t e a r a t e behave almost i d e n t i c a l l y w i t h r e s p e c t to t h e i r t r a n s i t i o n s and the temperatures o f those t r a n s i t i o n s . Therefore the d e t a i l e d x-ray i n v e s t i g a t i o n of sodium p a l m i t a t e by Nordsieck et a l (99) may provide some i n f o r m a t i o n . They decided that below the subwaxy r e g i o n the soap was e s s e n t i a l l y c r y s t a l l i n e . The subwaxy, waxy and superwaxy r e g i o n s they c l a s s i f i e d as a group w i t h hydrocarbon chains i n a loose hexagonal packing w i t h a common average o r i e n t a t i o n of the p o l a r end groups. Subneat and neat were a l s o c l a s s i f i e d as a group, but one i n which the common o r i e n t a t i o n of the end groups had disappeared. This would f i t the second moment change at 120\u00b0C but not tha t at 2 3 5 - 2 3 7\u00b0C which corresponds to the subneat to neat t r a n s i t i o n . T h e i r s u g g e s t i o n t h a t the subneat to neat - 93 -t r a n s i t i o n may mark the change from a s t r u c t u r e i n which the chains were i n a s t a t e of f r o z e n r o t a t i o n to a s t a t e of a c t u a l r o t a t i o n would provide an e x p l a n a t i o n f o r the second moment change i n t h i s r e g i o n . The s u g g e s t i o n of f r o z e n r o t a t i o n i n the subneat phase i s incompatible, however, w i t h the work of Grant (12), the o b s e r v a t i o n by Powell and Pudington (1+6) that the phases i n t h i s r e g i o n have the d e c i d e d l y l i q u i d - l i k e a b i l i t y to flow, and i n f r a r e d data to be mentioned below. I t i s a l s o i n c o n f l i c t w i t h the x-ray work of de B r e t t e v i l l e and McBain (1+5), on sodium s t e a r a t e i t s e l f , who p o i n t out that the hexagonal packing i n that soap probably a r i s e s from the s p i n n i n g of the hydrocarbon chains about t h e i r long axes i n the superwaxy and h i g h e r temperature phases. In a d d i t i o n they disagree w i t h the p r e c e d i n g grouping of s t r u c t u r a l l y s i m i l a r forms and s t a t e that the subwaxy and waxy forms are d e f i n i t e l y c r y s t a l l i n e while the superwaxy phase more n e a r l y resembles the subneat and neat forms. They b e l i e v e t h a t i n the l a s t three phases the c a r b o x y l a t e groups are f i x e d : w i t h r e s p e c t to each other w i t h the p a r a f f i n chains s p i n n i n g on t h e i r l o n g axes. So f a r other evidence has not confirmed the n.m.r. i n t e r p r e t a t i o n of the sodium s t e a r a t e h i g h temperature phases. Indeed the other evidence i s even c o n t r a d i c t o r y w i t h r e s p e c t to i t s e l f . I t may be p o s s i b l e that the sodium s t e a r a t e observed was not i n every case an anhydrous sample such as t h a t observed by n.m.r. This might account f o r - 9k -d i f f e r e n c e s i n apparent behaviour e s p e c i a l l y (36) i n the x-ray d i f f r a c t i o n r e s u l t s . A r e c e n t x-ray i n v e s t i g a t i o n of anhydrous sodium s t e a r a t e by S k o u l i o s and L u z z a t i (100), however, p r o v i d e s s t r o n g c o n f i r m a t i o n o f the n.m.r. i n t e r p r e t a t i o n . They c l a s s i f i e d the h i g h temperature phases i n t o the same groups as was done from n.m.r. evidence. The subwaxy, waxy, superwaxy and subneat phases were b e l i e v e d to form a group p o s s e s s i n g a two-dimensional r e c t a n g u l a r s t r u c t u r e . T h i s s t r u c t u r e c o n s i s t e d of a set of p a r a l l e l . r i b b o n s i n d e f i n i t e i n l e n g t h and packed i n a r e c t a n g u l a r a r r a y . The p o l a r groups f i t i n t o the ribbons and the hydrocarbon chains, i n a l i q u i d - l i k e s t a t e , f i l l up the r e s t o f the c e l l . The neat phase was found to be i n a l a m e l l a r s t r u c t u r e w i t h a d e c i d e d l y l i q u i d c h a r a c t e r w i t h s t r u c t u r e s i m i l a r to t h a t of the melt. This f i t s the, n.m.r. i n t e r p r e t a t i o n of (1) c o n s i d e r a b l e r o t a t i o n and f l a i l i n g of hydrocarbon chains i n the subwaxy to subneat phase r e g i o n s , (11) maintenance of the i o n i c l a y e r i n the f o r e g o i n g r e g i o n s f o l l o w e d by d i s r u p t i o n o f t h a t l a y e r at the subneat to neat t r a n s i t i o n , and (111) subsequent s i m i l a r i t y o f neat phase and melt. In a d d i t i o n they p l a c e d the subneat to neat t r a n s i t i o n at 238\u00b0C i n e x c e l l e n t agreement w i t h the 23\u00a3-237\u00b0C t r a n s i t i o n found by n.m.r. P i n a l c o n f i r m a t i o n of the n.m.r. i n t e r p r e t a t i o n comes from Chapman's (k) study of the i n f r a r e d s p e c t r a of sodium soaps. Prom the s p e c t r a of sodium p a l m i t a t e and - 9 5 -s t e a r a t e he deduced that i n the v i c i n i t y of 100\u00b0G the hydrocarbon chains begin to t w i s t and f l e x as evidenced by the l o s s of r e s o l u t i o n of c e r t a i n bands i n the 1 2 5 0 cm 1 r e g i o n and the decrease i n i n t e n s i t y of the methylene r o c k i n g band at 7 1 9 cm (The band, i n c i d e n t a l l y , .is s i n g l e due to t r i c l i n i c c r y s t a l s t r u c t u r e and p o s s i b l e hexagonal packing i n the h i g h temperature phases.) On h e a t i n g to about 1 2 0 - 1 3 0\u00b0C, the approximate range of the o second moment change at 1 2 0 C, a f u r t h e r decrease i n the - 1 i n t e n s i t y of the 719 cm band combined w i t h the disappearance of some other bands, suggests t h a t many more methylene groups are s p i n n i n g f r e e l y about the C-C bonds. T h i s change from a f a i r l y c r y s t a l l i n e s t a t e to one po s s e s s i n g some l i q u i d - l i k e c h a r a c t e r agrees w i t h the n.m.r. , o i n t e r p r e t a t i o n . Above 1 2 0 - 1 3 0 G the s p e c t r a are d e f i n i t e l y l i q u i d - l i k e being analogous to those at the f a t t y a c i d t r a n s i t i o n from c r y s t a l l i n e to l i q u i d phase. Methylene groups are s p i n n i n g f r e e l y and the p a r a f f i n chains are i n a l i q u i d - l i k e c o n d i t i o n w i t h m e l t i n g probably only being prevented by the st r o n g sodium and carbox y l a t e group a t t r a c t i o n . T h i s l i q u i d - c r y s t a l l i n e r e g i o n extends .at l e a s t to 2 0 0\u00b0C the h i g h e s t r e p o r t e d temperature. T h i s a g a i n i s c o n s i s t e n t w i t h the n.m.r. r e s u l t s and i t i s not s u r p r i s i n g that n.m.r. does not d i s t i n g u i s h between a s u c c e s s i o n of s i m i l a r , l i q u i d - l i k e phases u n t i l the breakdown of the i o n i c l a y e r permits a c t u a l d i f f u s i o n to take pl a c e about q.0C\u00b0 below the m e l t i n g p o i n t . - 96 -Sodium s t e a r a t e then c o n s i s t s of three g e n e r a l phases. There i s a c r y s t a l l i n e phase group below about o 1 2 0 C, a l i q u i d - c r y s t a l l i n e phase group between about 1 2 0 to 2 3 5\u00b0C, and a l i q u i d phase group from the l a s t temperature upwards. The sodium soap does not t h e r e f o r e melt i n a sudden c a t a s t r o p h i c process but goes through an intermediate r e g i o n between the e s s e n t i a l l y c r y s t a l l i n e s t r u c t u r e and the true m e l t i n g p o i n t . P r e m e l t i n g may c e r t a i n l y be s a i d to be o c c u r i n g i n t h i s r e g i o n . I t may o be considered as beginning i n the v i c i n i t y of 1 2 0 C and .0 r e a c h i n g a climax around 2 3 5 C above which temperature the sample i s e s s e n t i a l l y l i q u i d although w e l l below the m e l t i n g p o i n t ( 2 7 5 - 2 8 0 \u00b0 C ) . - 9 7 -i APPENDIX I REPRODUCTIONS OP REPRESENTATIVE EXPANDED INFRARED SPECTRA OP STEARIC, PALMITIC, MYRISTIC AND LAURIC ACIDS STEARIC ACID 1.3 \u00b0C 740 \u2014I\u2014 C M - ' 730 720 \u2014 1 L _ 710 \u2014 u 0.10 o H O > o m z 02055 0.30 MYRISTIC ACID - 102 -t APPENDIX I I REPRODUCTIONS OP REPRESENTATIVE HIGH RESOLUTION NUCLEAR MAGNETIC RESONANCE SPECTRA . OP SODIUM STEARATE S i n g l e a b s o r p t i o n s p e c t r a are shown i n each of s e t s one and two, but i n set one the i n d i c a t e d second moment i s f o r the averaged spectrum (not shown) while i n set two i t i s f o r the p a r t i c u l a r spectrum reproduced. S E T O N E RELATIVE SCALE IS DENOTED BY THE ATTENUATION VALUE. O I2I\u00b0C AHVi= 0.31 GAUSS \u2022AHI. = 0 .08 GAUSS .ATTENUATION = 1.7 O 131.5\u00b0C A H . \/ X = 0 . 2 6 GAUSS A H j =0.07 G A U S S ^ ATT. = 17 O W I 176 \u00b0C O A H y =0.22 GAUSS ^Ha=O.II GAUSS 2 \" ATT. = 1-7 SET ONE CONTINUED O 2 2 0 \u00b0 C AH V x =O. I5 GAUSS ^ H * = 0 . 0 6 GAUSS 1 ATT. = 1.2 v ^ O 225 .5 \u00b0C ^ v v , A H ^ = O . I 2 GAUSS \\ *HUQ . 07 G A U S S * ^ ^ ^ ^ 259~\"C ( B HIGHER ) ^ H ' \/ v * 0 . 0 2 GAUSS <*\u00bbH\\ ^ 1 0 \" + G A U S S 1 ATT. -S 1.5 \u2022 I20\u00b0C SET TWO CONTINUED \u2022V-226 \u00b0C ^ H y j O l O G A U S S A.H1=0.I3 G A U S S 2 -A T T = 1.0 2 3 5 \u00b0 C A H y x = 0 . 0 5 0 GAUSS V A H * =0.11 G A U S S Z ^ ^ v ^ A T T s. 0.7 \u2022 237\u00b0C (a HIGHER ) A H ' \/ ! 5*0.03 ^ GAUSS A H * ATT. s 0.2 * . I 0 - 4 \" G A U S S * ' - 1 0 7 -R E F E R E N C E S A . R . U b b e l o h d e , T r a n s . F a r a d . S o c , 3 4 , 2 8 9 ( 1 9 3 8 ) . M . R . B a r r , B . S c . T h e s i s , U n i v e r s i t y o f B r i t i s h C o l u m b i a , I 9 6 0 . L . J . B e l l a m y , T h e I n f r a r e d S p e c t r a o f C o m p l e x M o l e c u l e s . L o n d o n , M e t h u e n & C o . L t d . , 1958, C h a p t e r 2. D . C h a p m a n , J . C h e m . S o c , 78k (1958). R . G . S n y d e r , J . M o l . S p e c t r o s c o p y , 2 , 1 1 6 ( 1 9 6 1 ) . M . T u o t , J . L e c o m t e , L ' A c a d . d e s S c i . P a r i s , C o m p t e s R e n d u s , 2 1 6 , 339 (1943). H . W . T h o m p s o n , P . T o r k i n g t o n , P r o c . R o y . S o c . ( L o n d o n ) , A l 8 k . 3 (1945). R . S . S t e i n , G . B . B . M . S u t h e r l a n d , J . C h e m . P h y s . , 22, 1993 (1954). D . C h a p m a n , J . C h e m . S o c , 44.89 (1957). R . F . G r a n t , B . A . D u n e l l , C a n . J . C h e m . , 38 , 359 ( I 9 6 0 ) . M . R . B a r r , R . F . G r a n t , B . A . D u n e l l , t o b e p u b l i s h e d . R . F . G r a n t , P h d . T h e s i s , U n i v e r s i t y o f B r i t i s h C o l u m b i a , I 9 6 0 . A . R . U b b e l o h d e , A n a l . C h i m . A c t a , 12, 1 (1957). J . H . R e a d , D . M . G . L l o y d , T r a n s . F a r a d . S o c , 4 4 , 7 2 1 (1948). L . H u n t e r , S . S i e g e l , P h y s . R e v . , 6 1 , 84 (1942). A . R . U b b e l o h d e , Q u a r t . R e v . , 4 , 356 (1950). A . R . U b b e l o h d e , A n n . R e p t s . o n P r o g r e s s C h e m . , 3X> 1 6 7 (1940). A . R . U b b e l o h d e , B r i t . J . A p p l . P h y s . , 2 , 313 (1956). J . C . M c C o u b r e y , A . R . U b b e l o h d e , Q u a r t . R e v . , 364 ( 1 9 5 D -B u l l . U . S . B u r . S t a n d . , . 12, 69 (1915), a s c i t e d I n r e f . ( 1 6 ) A . V a n H o o k , L . S i l v e r , J . C h e m . P h y s . , 10, 686 (1942). E . S t e n h a g e n , E . v o n S y d o w , A r k i v . F o r K e m i , 6, 3 0 9 (1953\/4) E . v o n S y d o w , A c t a C h e m . S c a n d . , 9_, 1685 (1955). - 108 -E. von Sydow, A r k i v . For Keral, 2 , 2 3 1 ( 1 9 5 6 ) . T. Malkin , \"The M o l e c u l a r S t r u c t u r e and Polymorphism of F a t t y A c i d s and T h e i r D e r i v a t i v e s , \" R.T. Holman, W.O. Lundberg, T. Malkin, eds.. Progress i n the Chemistry of F a t s and Other L i p i d s , v o l . 1 , London, Pergamon Press, L t d . , 1 9 5 2 , p . l . R.T. O'Connor, \"X-Ray D i f f r a c t i o n and Polymorphism,\" K.S. Markley, ed., F a t t y A c i d s , p a r t 1, New York, I n t e r s c i e n c e Pub., Inc., I960. V. Vand, W.M. Mor l e y , T.R. Lomer, A c t a C r y s t . , 4 , 3 2LL ( 1 9 5 D . S. Abrahamson, E. von Sydow, A c t a C r y s t . , 2 , 5 9 1 ( 1 9 5 4 ) ' F. D. La Tour, Le Polymorphisme des Ac i d e s G-ras. P a r i s , Hermann, 1 9 3 6 , as c i t e d i n A.R. Verma, Proc. Roy. Soc. . (London), A228, 3 4 ( 1 9 5 5 ) -J.M. Cowley, Trans. Farad. S o c , 4 4 , 60 ( 1 9 4 8 ) . V. Vand, T.R. Lomer, A. Lang, A c t a C r y s t . , 2, 2 1 4 ( 1 9 4 9 ) . T.R. Lomer, Nature, 17_6, 653 ( 1 9 5 5 ) . W.S. S i n g l e t o n , T.L. Ward, F.G. D o l l e a r , J . Am. O i l Chemists' S o c , \u00a31, 143 ( 1 9 5 0 ) . J . Thibaud, F.D. La Tour, J . de Chim. Phys., 29., 153 ( 1 9 3 2 ) , as c i t e d i n r e f . ( 3 3 ) . G. K o k o t a i l o , T h e s i s , Temple U n i v e r s i t y , as c i t e d i n r e f . (12). R.D. Void, J.D. Grandine 2 n d . , H. Schott, J . Phys. Chem., \u00a36, 128 ( 1 9 5 2 ) . A.J. S t o s i c k , J . Chem. Phys., 18, 1 0 3 5 ( 1 9 5 0 ) . V. Vand, A. A i t k e n , R.K. Campbell, A c t a C r y s t . , 2, 398 ( 1 9 4 9 ) . H. E. Wirth, W.W. Wellman, J . Phys. Chem., 60, 9 2 1 ( 1 9 5 6 ) . D.P. Benton, P.G. Howe, R. Farnand, I.E.. Puddington, Can. J . Chem., H , 1 7 9 8 ( 1 9 5 5 ) . W. G a l l a y , I.E. Puddington, Can. J . Research, B22, 90 ( 1 9 4 4 ) . - 109 -(1+2) P. Southam, I.E. Puddington, Can. J . Research, B2\u00a3, 121 (191+7). (1+3) D.P. Benton, P.G. Howe, I.E. Puddington, Can. J . Chem., H , 1 3 8 4 ( 1 9 5 5 ) . (1+1+) 0 . Stainsby - j R. Parnand, I.E. Puddington, Can. J . Chem., 29., 8 3 8 ( 1 9 5 D . (1+5) A. De B r e t t e v i l l e , J.W. McBain, J . Chem. Phys., 11, 1+26 ( 1 9 4 3 ) . ( 4 6 ) B.D. Powell, I.E. Puddington, Can. J . Chem., 3.1, 828 ( 1 9 5 3 ) . ( 4 7 ) R.D. Void, J . Am. Chem. S o c , 61, 2 9 1 5 ( 1 9 4 D . ( 4 8 ) H.H. N i e l s e n , R.A. Oetjen, \" I n f r a r e d Spectroscopy,\" W.G. B e r l , ed.. P h y s i c a l Methods i n Chemical A n a l y s i s . 2nd. ed., v o l . 1 , New York, Academic Press, Inc., I960. ( 4 9 ) A.B.P. Duncan, \"Theory of I n f r a r e d and Raman S p e c t r a , \" \u00a5. West, ed., Chemical A p p l i c a t i o n s of Spectroscopy. New York, I n t e r s c i e n c e Pub. Inc., 1 9 5 6 (A. Weissberger, ed., Techniques of Organic Chemistry, v o l . 9 ) . ( 5 0 ) G. Herzberg, M o l e c u l a r S p e c t r a and M o l e c u l a r S t r u c t u r e . v o l . 2 , I n f r a r e d and Raman S p e c t r a of Polyatomic Molecules. 9 New York, D. Van Nostrand Co. Inc., I960, p.62. ( 5 D \\ , pp. 1 3 f . ( 5 2 ) ; \u2022 , pp. 3 7 0 f . ( 5 3 ) R.N. Jones, C. Sandorfy, \" A p p l i c a t i o n of I n f r a r e d and Raman Spectrometry to t h e - E l u c i d a t i o n of M o l e c u l a r S t r u c t u r e , \" W. West, ed., Chemical A p p l i c a t i o n s of Spectroscopy. New York, I n t e r s c i e n c e Pub. Inc., 1 9 5 6 (A. Weissberger, ed., Techniques o f Organic Chemistry, v o l . 9 ) . ( 5 4 ) J \u00ab J . F \u00b0 x , A.E. M a r t i n , Proc. Roy. Soc. (London), A175. 208, 2 3 4 ( 1 9 4 0 ) . ( 5 5 ) J . J . Pox, A.E. M a r t i n , Proc. Roy. Soc. (London), A167. 2 5 7 ( 1 9 3 8 ) . ( 5 6 ) R.G. S i n c l a i r , A.P. McKay, R.N. Jones, J . Am. Chem. S o c , 24, 2 5 7 0 ( 1 9 5 2 ) . ( 5 7 ) R.C. Gore, E.S. Waight, \" I n f r a r e d L i g h t A b s o r p t i o n , \" E.A. Brand, P.C. Nachod,-eds., Determination o f Organic S t r u c t u r e s by P h y s i c a l Methods. New York, Academic Press, 1 9 5 5 . - 110 -(58) L . J . Bellamy., The I n f r a r e d S p e c t r a of Complex Molecules. London, Methuen & Co. L t d . , 1958, Chapter 10. (59) N. Sheppard, G..B.B.M. Sutherland, Nature, 739 (1947). (60) G-.B.B.M. Sutherland, A.V. Jones, Nature, 160. 567 (1947). (61) D. Chapman, J.. Chem. S o c , kk89 (1957). (62) R.F. Ho l l a n d , J.R. N i e l s e n , J . Molec. Spectroscopy, 8, 383 (1962). (63) R.S. S t e i n , J . Chem. Phys., 21, 73k (1955). (6k) R.G. Snyder, J . Molec. Spectroscopy, 4, k l l ( i 9 6 0 ) . (65) H.S. Gutowsky, \" A n a l y t i c a l A p p l i c a t i o n s of Nuclear Magnetic Resonance,\" W.G. Ber'l, ed., P h y s i c a l Methods i n Chemical A n a l y s i s , v o l . 3 , New York, Academic Press, Inc., 1956. (66) E.R. Andrew, Nuclear Magnetic Resonance, Cambridge, Cambridge U n i v e r s i t y Press, 19i>6, Chapter 2. (67) J.P. Ll o y d , G.E. Pake, Phys. Rev., 24, 579 (1954). (68) H.S. Gutowsky, \"Nuclear Magnetic Resonance,\" G.K. R o l l e f s o n , ed., Annual Review o f P h y s i c a l Chemistry, v o l . 5 , S t a n f o r d , Annual Reviews, Inc., 1954\u00ab (69) G.E. Pake, J . Chem. Phys., 16, 327 (1948). (70) E.R. Andrew, R.J. Bersohn, J . Chem. Phys., 18, 159 (1950). (71) H.S. Gutowsky, G.B. Kistiakowsky, G.E. Pake, E.M. P u r c e l l , J . Chem. Phys., 11, 972 (1949). (72) R.J. Bersohn, H.S. Gutowsky, G.E. Pake, J . Chem. Phys., 22, 643 (1954). (73) J.N. Shoolery, H.E. Weaver, \"Nuclear and Paramagnetic Resonance,\" G.K. R o l l e f s o n , ed., Annual Review of P h y s i c a l Chemistry, v o l . 6 , S t a n f o r d , Annual Reviews, Inc., 1955. (74) J.H. Van Vleck, Phys. Rev., 24, 1168 (1948). (75) J.A.S. Smith, Quart. Rev., 2, 279 (1953). (76) E.R. Andrew, Nuclear Magnetic Resonance. Cambridge., Cambridge U n i v e r s i t y P r e s s , 1958, C h a p t e r 6 . \" ' '\u2022 \" - I l l -( 7 7 ) J.B. Brown, D.K. Kolb, \" A p p l i c a t i o n s o f Low Temperature C r y s t a l l i z a t i o n i n tlie S e p a r a t i o n of the F a t t y A c i d s and T h e i r Compounds,\" R.T. Holman et a l , Progress i n the Chemistry of Fa t s and Other L i p i d s , v o l . 3 , 1 9 5 5 , p. 5 7 . ( 7 8 ) K.S. Markley. F a t t y A c i d s . New York, I n t e r s c i e n c e Pub., Inc., 1 9 4 7 , p . I l k . ( 7 9 ) F. F r a n c i s , H.S. P i p e r , J . Am. Chem. S o c , 61, 5 7 7 ( 1 9 3 9 ) . (80) Perkin-Elmer Instrument Manual 990 - 9 0 0 3 f o r Model 21B I n f r a r e d Spectrometer. (81) J . J . K i r k l a n d , A n a l . Chem., 2 1 , 1537 ( 1 9 5 5 ) . (82) R.F. Grant, p r i v a t e communication, Sept. 1962. (83) J.K., Brown, N. Sheppard, D.M. Simpson, D i s c . Farad. S o c , 8\/2, 2 7 k ( 1 9 5 0 ) . ( 8 k ) J.K. Brown, N. Sheppard, D.M. Simpson, P h i l . Trans. Roy. Soc. (London), A2k7. 3 5 ( 1 9 5 4 \/ 5 ) . ( 8 5 ) C.Y. Liang, S. Krimm, G.B.B.M. Sutherland, J . Chem. Phys., 2 5 , 5 4 3 ( 1 9 5 6 ) . ( 8 6 ) S. Krimm, C.Y. Liang, G.B.B.M. Sutherland, J . Chem. Phys., 2SL, 5 4 9 ( 1 9 5 6 ) . ( 8 7 ) S. Krimm, Phys. Rev., 24, 1 4 2 6 ( 1 9 5 4 ) . ( 8 8 ) D. Chapman, S i x t h I n t e r n a t i o n a l S p e c t r o s c o p i c Colloquium, Amsterdam, 1 9 5 6 , as c i t e d i n ( 9 ) . (89.) M.C. Tobin, J . Chem. Phys., 21, 891 ( 1 9 5 5 ) . (90) A.'E. Smith, J . Chem. Phys., 21, 2229 ( 1 9 5 3 ) . (91) P.J. C o r i s h , D. Chapman, J . Chem. S o c , 1 7 4 6 ( 1 9 5 7 ) . (92) V. D a n i e l , Advances i n P h y s i c s , 2, 4 5 0 ( 1 9 5 3 ) . ( 9 3 ) R.W. Crowe, C P . Smyth, J . Am. Chem. S o c , Jl, 5 4 0 1 ( 1 9 5 D ( 9 4 ) R.L. C o l l i n s , J . Poly. S c i . , 28, 6 7 ( 1 9 5 8 ) . ( 9 5 ) A. M u l l e r , Proc. Roy. Soc. (London), A127. 4 1 7 (1930). ( 9 6 ) L. P a u l i n g , Phys. Rev., 16, 4 3 0 (1930). ( 9 7 ) J.G. Powles, P r o c Phys. S o c (London), B69_, 281 ( 1 9 5 6 ) . - 112 -(98) J.G. Powles, H.S. Gutowsky, J . Chem. Phys., 23_, 1692 (1955). (99) H. Nordsleck, P . B . Rosevear, R.H. Ferguson, J . Chem. Phys., 16, 175 (1948). '(100) A. S k o u l i o s , V. L u z z o t i , Nature, 181, 1310 (1959). ","@language":"en"}],"Genre":[{"@value":"Thesis\/Dissertation","@language":"en"}],"IsShownAt":[{"@value":"10.14288\/1.0061947","@language":"en"}],"Language":[{"@value":"eng","@language":"en"}],"Program":[{"@value":"Chemistry","@language":"en"}],"Provider":[{"@value":"Vancouver : University of British Columbia Library","@language":"en"}],"Publisher":[{"@value":"University of British Columbia","@language":"en"}],"Rights":[{"@value":"For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https:\/\/open.library.ubc.ca\/terms_of_use.","@language":"en"}],"ScholarlyLevel":[{"@value":"Graduate","@language":"en"}],"Title":[{"@value":"A study of premelting in the C-forms of stearic, palmitic, myristic and lauric acids by infrared spectroscopy and in anhydrous sodium stearate by high resolution nuclear magnetic resonance spectroscopy.","@language":"en"}],"Type":[{"@value":"Text","@language":"en"}],"URI":[{"@value":"http:\/\/hdl.handle.net\/2429\/38354","@language":"en"}],"SortDate":[{"@value":"1962-12-31 AD","@language":"en"}],"@id":"doi:10.14288\/1.0061947"}