UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Orientation of molecular solutes in nematic liquid crystals : size and shape effects 1986

You don't seem to have a PDF reader installed, try download the pdf

Item Metadata

Download

Media
UBC_1986_A6_7 K66_5.pdf [ 4.14MB ]
UBC_1986_A6_7 K66_5.pdf
Metadata
JSON: 1.0059471.json
JSON-LD: 1.0059471+ld.json
RDF/XML (Pretty): 1.0059471.xml
RDF/JSON: 1.0059471+rdf.json
Turtle: 1.0059471+rdf-turtle.txt
N-Triples: 1.0059471+rdf-ntriples.txt
Citation
1.0059471.ris

Full Text

ORIENTATION OF MOLECULAR SOLUTES IN NEMATIC LIQUID CRYSTALS: SIZE AND SHAPE EFFECTS by KOK, MEI YENG B . S c . ( H o n s . ) , The U n i v e r s i t y of B r i t i s h Columbia , 1985 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES (Department of Chemistry) We accept t h i s t h e s i s as conforming t o the r e q u i r e d s tandard THE UNIVERSITY OF BRITISH COLUMBIA SEPTEMBER, 1986 © Kok, Mei Yeng, 1986 9 5 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 an advanced degree a t 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 , I agree 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 and s t u d y . I f u r t h e r agree 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 purposes may be g r a n t e d by t h e head o f my department o r by h i s o r h e r 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 . Department o f The U n i v e r s i t y o f B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 4-k Date E - 6 rvan - i i - A B S T R A C T An u n d e r s t a n d i n g of the mechanisms of o r i e n t a t i o n o f s o l u t e s i n a n i s o t r o p i c s o l v e n t s i s o f fundamental importance i n the theory of l i q u i d c r y s t a l l i n e systems. A s y s t e m a t i c s tudy o f these mechanisms i s p r e s e n t l y b e i n g conducted i n t h i s and o ther l a b o r a t o r i e s . As p a r t of t h i s i n v e s t i g a t i o n , the o r i e n t a t i o n a l order of a s e r i e s o f C 2 V s o l u t e s i n the l i q u i d c r y s t a l m i x t u r e 55 wt% 1132 (Merck ZLI 1132) and 45 wt% p a r t i a l l y d e u t e r a t e d EBBA ( N - ( 4 - e t h o x y b e n z y l i d e n e ) - 2 , 6 - d i d e u t e r o - 4 - n - b u t y l a n i l i n e ) was s t u d i e d u s i n g NMR s p e c t r o s c o p y . T h i s technique p r o v i d e s a d e s c r i p t i o n o f the average o r i e n t a t i o n o f a s o l u t e i n terms o f the o r d e r parameters . The r e s u l t s o b t a i n e d i n d i c a t e a good c o r r e l a - t i o n between order parameters and the s i z e and shape o f the s o l u t e s . A model based on s h o r t range h a r d body i n t e r a c t i o n s , which depend on the dimensions o f the s o l u t e , was used to p r e d i c t o r i e n t a t i o n a l o r d e r i n g . E x c e l l e n t agreement was o b t a i n e d between observed and c a l c u l a t e d order parameters . These r e s u l t s p r o v i d e s u p p o r t i v e evidence t h a t the mecha- nism r e s p o n s i b l e f o r o r i e n t a t i o n i n the 55 wt% 1132 system i s s h o r t range h a r d body i n t e r a c t i o n s . A s i d e s tudy was conducted on the o r d e r i n g o f f u r a n and thiophene i n the l i q u i d c r y s t a l l i n e s o l v e n t s 1132 and EBBA. Temperature depen- dence o f order parameters i n 55 wt% 1132 were examined. O r i e n t a t i o n i n 1132 and EBBA and temperature dependence i n 55 wt% 1132 can be e x p l a i n e d i n terms o f : ( i ) the s h o r t range i n t e r a c t i o n s dependent on the dimensions of the i i i - solute, and ( i i ) the i n t e r a c t i o n between the molecular quadrupole moment of the solute and the average e l e c t r i c f i e l d gradient which i s due to the solvent. - i v - TABLE OF CONTENTS Page ABSTRACT i i TABLE OF CONTENTS i v LIST OF TABLES v i LIST OF FIGURES v i i LIST OF ABBREVIATIONS i x ACKNOWLEDGEMENTS x I . INTRODUCTION . . . . . 1 1.1 L i q u i d C r y s t a l l i n e Systems 3 1 .1 .1 D e s c r i p t i o n 3 1 .1 .2 I n f o r m a t i o n o b t a i n a b l e from NMR 5 1 .1 .3 On the o r i e n t a t i o n a l order 10 1.2 O b j e c t i v e s o f t h i s Thes i s 14 I I . THEORY 15 I I . 1 NMR o f p a r t i a l l y o r i e n t e d molecules 16 I I . 2 S i z e and shape model 20 - V - I I I . EXPERIMENTAL 28 111.1 D e u t e r a t i o n o f 4 - b u t y l a n i l i n e 30 111.2 P r e p a r a t i o n of EBBA 31 I I I . 3 P r e p a r a t i o n of 55 wt% 1132 mix ture 32 I I I . 4 P r e p a r a t i o n of NMR Samples 32 I I I . 5 Spectroscopy 33 I I I . 6 S p e c t r a l a n a l y s i s . 35 I V . RESULTS 38 I V . 1 S o l u t e s i n 55 wt% 1132 39 I V . 2 Furan and thiophene 62 V. DISCUSSION 70 V . l O r i e n t a t i o n of s o l u t e s i n 55 wt% 1132 72 V . 2 S i z e and shape model 74 V . 2 . 1 P r e d i c t i o n o f o r i e n t a t i o n 74 V . 2 . 2 Causes o f d e v i a t i o n s i n p r e d i c t e d o r i e n t a t i o n s 80 V . 2 . 3 E f f e c t s o f temperature and c o n c e n t r a t i o n v a r i a t i o n s 83 V . 3 Furan and thiophene 87 V . 3 . 1 Component l i q u i d c r y s t a l s tudy 87 V . 3 . 2 Temperature s tudy 92 V I . CONCLUSION 101 V I I . BIBLIOGRAPHY 103 APPENDIX Table o f order parameters 107 - v i - LIST OF TABLES Table Page I V . 1 E x p e r i m e n t a l d i p o l a r c o u p l i n g s ( H z ) , i n d i r e c t c o u p l i n g s ( H z ) , chemica l s h i f t d i f f e r e n c e s , and the rms e r r o r s o b t a i n e d from the program LEQUOR f o r s o l u t e s i n 55 wt% 1132 a t 301.4 K 43 I V . 2 The geometry o f the m o l e c u l e s : ( i ) l i t e r a t u r e ( i i ) e x p e r i m e n t a l 53 I V . 3 E x p e r i m e n t a l and c a l c u l a t e d order parameters o f s o l u t e s i n 55 wt% 1132 a t 301.4 K 59 I V . 4 E x p e r i m e n t a l d i p o l a r c o u p l i n g s ( H z ) , chemica l s h i f t d i f f e r e n c e s and the rms e r r o r s o b t a i n e d from the program LEQUOR f o r f u r a n and thiophene i n 55 wt% 1132 a t v a r i o u s temperatures 63 I V . 5 E x p e r i m e n t a l d i p o l a r c o u p l i n g s ( H z ) , chemica l s h i f t d i f f e r e n c e s and the rms e r r o r s o b t a i n e d from the program LEQUOR f o r f u r a n and thiophene i n 1132 and EBBA . 66 I V . 6 E x p e r i m e n t a l order parameters of f u r a n and thiophene i n 55 wt% 1132 a t v a r i o u s temperatures . . 67 I V . 7 E x p e r i m e n t a l order parameters of f u r a n and thiophene i n 1132 and EBBA 69 V . l E l e c t r i c f i e l d g r a d i e n t - q u a d r u p o l e moment mechanism: Order parameters ( exper imenta l and c a l c u l a t e d ) of f u r a n and thiophene i n 1132 and EBBA 91 - v i i - LIST OF FIGURES F i g u r e Page 1.1 Arrangement o f molecules i n a nematic phase . . . 4 1.2 The m o l e c u l a r arrangement i n a c h o l e s t e r i c mesophase . 6 1.3 S t r u c t u r e o f a smect ic phase 7 1.4 P r o t o n NMR spectrum of hexadiyne p a r t i a l l y o r i e n t e d i n the l i q u i d c r y s t a l EBBA . . . . . . . 9 11.1 E l a s t i c tube model f o r the s h o r t range i n t e r a c t i o n s between s o l u t e and l i q u i d c r y s t a l 23 11.2 P r o j e c t i o n o f s o l u t e i n X - Y p lane 27 I I I . l Deuteron NMR spectrum o f D2 p a r t i a l l y o r i e n t e d i n the l i q u i d c r y s t a l 55 wt% 1132 36 I V . 1 P r o t o n NMR spectrum o f 1,4-dibromobenzene p a r t i a l l y o r i e n t e d i n 55 wt% 1132 (A) e x p e r i m e n t a l (B) computer s i m u l a t e d 40 I V . 2 P r o t o n NMR spectrum o f f luorobenzene p a r t i a l l y o r i e n t e d i n 55 wt% 1132 (A) e x p e r i m e n t a l (B) computer s i m u l a t e d 41 I V . 3 Deuteron NMR spectrum o f d e u t e r a t e d EBBA 42 V . l S i z e and shape model : c a l c u l a t e d versus e x p e r i m e n t a l order parameters S x x o f s o l u t e s i n 55 wt% 1132 75 V . 2 S i z e and shape model : c a l c u l a t e d versus e x p e r i m e n t a l order parameters S ™ o f s o l u t e s i n 55 wt% 1132 . . . . 76 V . 3 S i z e and shape model : c a l c u l a t e d versus e x p e r i m e n t a l order parameters S 2 Z of s o l u t e s i n 55 wt% 1132 78 V . 4 S i z e and shape model : c a l c u l a t e d versus e x p e r i m e n t a l Sxx " -*yy parameters TJ = o f s o l u t e s i n 55 wt% 1132 . . 79 s z z - v i i i - V . 5 T h e o r e t i c a l versus e x p e r i m e n t a l unsea led order parameters : S x x , S ™ and S z z o f molecules i n 55 wt% 1132 85 V . 6 T h e o r e t i c a l versus s c a l e d exper imenta l order parameters : S x x , Syy, S Z 2 o f molecules i n 55 wt% 1132 86 V . 7 E l e c t r i c f i e l d g r a d i e n t - q u a d r u p o l e moment mechanism: c a l c u l a t e d versus e x p e r i m e n t a l order parameters S e f g o f f u r a n and thiophene i n 1132 89 V . 8 E l e c t r i c f i e l d g r a d i e n t - q u a d r u p o l e moment mechanism: c a l c u l a t e d versus e x p e r i m e n t a l order parameters s e f g ° f f u r a n and thiophene i n EBBA 90 V . 9 Temperature dependence of the order parameters : S x x ( c a l c u l a t e d and exper imenta l ) o f f u r a n i n 55 wt% 1132 95 V . 1 0 Temperature dependence o f the order parameters : Syy ( c a l c u l a t e d and exper imenta l ) o f f u r a n i n 55 wt% 1132 96 V . l l Temperature dependence of S z z ( c a l c u l a t e d and exper imenta l ) o f f u r a n i n 55 wt% 1132 97 V.12 Temperature dependence o f S x x ( p r e d i c t e d and exper imenta l ) o f thiophene 55 wt% 1132 98 V . 1 3 Temperature dependence of Syy ( p r e d i c t e d and e x p e r i m e n t a l ) o f thiophene i n 55 wt% 1132 99 V .14 Temperature dependence o f S z z ( p r e d i c t e d and e x p e r i m e n t a l ) o f thiophene i n 55 wt% 1132 100 i x - LIST OF ABBREVIATIONS N - ( 4 - e t h o x y b e n z y l i d e n e ) - 4 - n - b u t y l a n i l i n e Merck ZLI 1132 : mix ture o f C 1 6 H 2 i N , C18H25N> C20H29N> c 2 4 h 2 9 n . M i x t u r e o f 1132-EBBA, weight c o m p o s i t i o n : 55% 1132 and 45% EBBA. N u c l e a r magnetic resonance T e t r a t h i o f u l v a l e n e E l e c t r i c f i e l d g r a d i e n t Order parameter Order parameter which d e s c r i b e s o r i e n t a t i o n i n the pq d i r e c t i o n c . c °xx °yy The asymmetry parameter , d e f i n e d a s : s z z E l a s t i c f o r c e constant Standard temperature and p r e s s u r e I n c l u d e s C 2 v and D 2 ^ molecules X - ACKNOWLEDGEMENT I wish to express my grateful thanks to Dr. E.E. Burnell for his encouragement and guidance during the course of this work. It has been an interesting and rewarding experience. I am indebted to these colleages: J . Delikatny, J . Rendell and especially A. van der Est whose collaboration I benefitted from. I am grateful to them for their patience, generosity with their time and the help they have given me with the theoretical and experimental aspects of this project. I would like to thank Dr. Weiler for the sample of TTF. My thanks are also extended to Dr. S.O. Chan and the technical staff of the NMR Service lab. I should also like to thank Rani Theeparajah for typing this thesis. The financial assistance in the form of a University Graduate Fellowship and a teaching assistantship is gratefully acknowledged. Most importantly, I would like to thank my husband, Andrew, for his patience and understanding. His optimism and unfailing cheerfulness contributed significantly to the completion of this work. - x i - To my sister Mei-Leng - 1 - CHAPTER I INTRODUCTION - 2 - I. INTRODUCTION The exact nature of the mechanisms of o r i e n t a t i o n a l order i n the theory of l i q u i d - c r y s t a l l i n e systems i s not f u l l y understood. - An understanding of these phy s i c a l i n t e r a c t i o n s i s of major importance i n studies such as i n the determination of the function of b i o l o g i c a l membranes, and the i n d u s t r i a l use of l i q u i d c r y s t a l s as di s p l a y devices. Such knowledge could also lead to a better understanding of intermole- cular forces i n the l i q u i d phase. L i q u i d c r y s t a l molecules are large and e x i s t i n many d i f f e r e n t conformations.- I t was concluded that i t would be d i f f i c u l t to obtain a be t t e r fundamental understanding from studies on these large molecules due to t h e i r f l e x i b i l i t y . The l o g i c a l s t a r t i n g point f o r a systematic i n v e s t i g a t i o n was to use small molecules disso l v e d i n l i q u i d c r y s t a l solvents.- 1 The primary aims have been to understand ( i ) the orienta- t i o n a l behaviour of the solutes and ( i i ) the intermolecular forces between solutes and the l i q u i d c r y s t a l molecules responsible f o r t h i s behaviour. In t h i s t h e s i s , an i n v e s t i g a t i o n of the in t e r a c t i o n s respon- s i b l e f o r the o r i e n t a t i o n of small solutes i n l i q u i d c r y s t a l l i n e systems i s reported. The method used f o r the study of the anisotropic i n t e r - actions of molecules dissolved i n anisotropic solvents i s nuclear magnetic resonance spectroscopy (NMR). - 3 - 1.1 Liquid C r y s t a l l i n e Systems I.1.1 Description The f i r s t 'liquid crystalline' state was discovered by an Austrian botanist, Frederick Reinitzer in 1888.^ He found that the compound he synthesized, cholestryl benzoate, appeared to have two melting points i.e. 145°C and 179°C. At 145°C, the solid melted to form a cloudy liquid which became clear at 179°C. In 1904, Lehman found that the cloudy intermediate was birefringent^ and hence anisotropic, and he therefore suggested the name 'liquid crystal' for i t . Since then, i t has been found that one of every two hundred pure organic compounds exhibits the liq u i d crystalline state. The liquid crystals referred to thus far are called thermotropics because they exhibit liquid c r y s t a l l i n i t y over a certain temperature range. Another major group is the lyotropic liquid crystals and these are formed by mixing two or more components. The best known examples of this group are aqueous soap solutions. The properties of liquid crystals are intermediate between the liqu i d and solid state. These include the rotational and translational mobility of liquids and the optical properties of solids. The molecules in the liq u i d crystalline state have more order than those in the liquid state but less than those in the solid state. The molecules that form thermotropic liquid crystals are generally elongated. These molecules usually contain benzene rings and often have strong dipoles towards their centres and weak dipoles towards their - 4 - ends. Due to i n t e r m o l e c u l a r f o r c e s , these molecules tend to o r i e n t w i t h t h e i r longest axes p a r a l l e l to each other. The thermotropic l i q u i d c r y s t a l s may be d i v i d e d i n t o three phases namely, nematic, c h o l e s t r i c and smectic. Nematic phase - The nematic phase ( F i g . 1.1) has the lowest order of the three phases. This phase, i f present always preceeds the t r a n s i t i o n to the i s o t r o p i c l i q u i d . The o r d e r i n g c o n s i s t s of a p r e f e r r e d p a r a l l e l arrangement of the long axes of la r g e groups of molecules. In the absence of e x t e r n a l f o r c e s , the p r e f e r r e d d i r e c t i o n of the long axes of the molecules i s not constant over l a r g e areas but v a r i e s continuously w i t h p o s i t i o n . Fig. 1.1: Arrangement of molecules in a nematic phase, e.g. 4-4'-dimethoxyazoxybenzene - 5 - C h o l e s t e r i c phase - The c h o l e s t e r i c phase (Fig. 1.2), regarded as a s p e c i a l case of the nematic phase, occurs only i n o p t i c a l l y active substances. I t has a layered structure, and within the layers the molecules are oriented p a r a l l e l to each other. The d i r e c t i o n of the molecular axes i n each layer i s , however, s l i g h t l y displaced with respect to adjacent layers, and the o v e r a l l displacement follows a h e l i c a l arrangement. Smectic phase - For a given l i q u i d c r y s t a l , t h i s higher ordered phase (Fig. 1.3) occurs at lower temperatures than the nematic and c h o l e s t r i c phases. The molecules are arranged i n layers with t h e i r long axes p a r a l l e l to each other. 1.1.2 Information obtainable from NMR Spectroscopy In nuclear magnetic resonance experiments, the l o c a l magnetic f i e l d s at the n u c l e i , which determine the various t r a n s i t i o n frequen- cies , change with the o r i e n t a t i o n of the molecules r e l a t i v e to the external f i e l d . For solutes dissolved i n i s o t r o p i c solvents, there i s r a p i d i s o t r o p i c molecular motion. Consequently, d i p o l a r and quadrupolar couplings and the anisotropy i n the scalar couplings and chemical s h i f t s which depend on o r i e n t a t i o n average to zero. Their NMR spectra are then governed by the average chemical s h i f t s and i n d i r e c t coupling constants between the n u c l e i . ^ - 6 - Fig. 1 . 2 : The molecular arrangement in a cholesteric mesophase e.g. cholestryl propionate. mesophase, SMECTIC B SMECTIC A Fig. 1.3 The structure of a smectic phase, e.g. 4-4'-diethyl- azoxybenzoate - 8 - For solutes i n l i q u i d c r y s t a l l i n e solvents, the motion remains f a s t on the NMR time scale. However, due to the anisotropic environment of the molecules, d i f f e r e n t molecular orientations are no longer equally probable.^ The NMR spectra are now weighted averages over a l l orienta- tions . Important and useful information such as d i p o l a r and quadrupolar couplings, and anisotropies i n chemical s h i f t s and i n d i r e c t couplings can now be measured. The nematic phase i s most u s e f u l for examining the anisotropic properties of small solute molecules because i t orients uniformly and e a s i l y i n a magnetic f i e l d . The ^H NMR spectrum of pure l i q u i d c r y s t a l s ( i n the nematic phase) i s usu a l l y not resolved and has l i t t l e observable f i n e structure. This i s due to the large number of protons i n the l i q u i d c r y s t a l s which gives r i s e to many energy l e v e l s . This multitude of energy l e v e l s produces many c l o s e l y spaced t r a n s i t i o n s r e s u l t i n g i n a spectrum which i s a broad envelope. The ^H NMR spectra of oriented solute molecules give r e l a t i v e l y sharp l i n e s and the d i r e c t dipole- dipole i n t e r a c t i o n i s manifested by the f i n e structure i n the spectrum. This spectrum i s superimposed on that of the l i q u i d c r y s t a l which i s a broad, featureless background s i g n a l . The spectrum of 2,4-hexadiyne, dissolved i n the nematic phase of EBBA i s as shown i n F i g . 1.4. The spectrum of the l i q u i d c r y s t a l i t s e l f i s broad and merges into the base l i n e . The solute spectrum i s well resolved i n sharp l i n e s , with a l i n e width of 2 Hz which i s t y p i c a l of solutes i n nematic phases. The f i r s t NMR experiments of solutes oriented i n l i q u i d c r y s t a l l i n e solvents were reported by Saupe and Englert i n 1963.^'^ Since then the F i g . 1.4 - 10 - NMR spectroscopy of oriented molecules has developed r a p i d l y , the primary aim being the study of d i r e c t d i p o l a r spin-spin couplings, which provide information on the molecular geometry of the solute.^ This has r e s u l t e d i n the accumulation of a large body of s t r u c t u r a l data on d i f f e r e n t kinds of compounds dissolved i n anisotropic phases. Despite the number of compounds which have been studied, the exact nature of the o r i e n t a t i o n a l mechanisms i n l i q u i d c r y s t a l s i s s t i l l not f u l l y known. 1.1.3 L i q u i d C r y s t a l l i n e Systems - On the O r i e n t a t i o n a l Order Over the years, studies have l e d to several suggestions concerning the mechanism of solute o r i e n t a t i o n . These include d i s p e r s i o n fo r c e s , - ^ s i z e and shape, and moments of i n e r t i a , ̂ -• of the solutes. These models, however, do not adequately explain many experimental r e s u l t s . In recent studies on methane-^"-** and hydrogen^ • • > and t h e i r deuterated analogs by Burnell et a l . , a better understanding of the mechanism of solute o r i e n t a t i o n has been achieved. In these studies, e x c e l l e n t agreement was obtained between the experimental and t h e o r e t i - c a l order parameters by assuming that the solvent-solute i n t e r a c t i o n i s of second order t e n s o r i a l form. For hydrogen, the r a t i o of quadrupolar to d i p o l a r coupling con- stants, *Vn> should be a molecular property and t h i s value should be the same as that measured i n the gas phase by molecular beam magnetic resonance studies.^- However, the r a t i o s obtained^ f o r HD and D 2 were - 11 - 7% lower than expected f o r gas phase r e s u l t s . This suggests that the deuterons i n the D 2 and HD were experiencing the presence of an external e l e c t r i c f i e l d gradient (efg) due to the l i q u i d c r y s t a l environment. I t was also suggested that the i n t e r a c t i o n between t h i s e l e c t r i c f i e l d gradient and the molecular quadrupolar moment of the solutes accounts fo r most of the molecular o r i e n t a t i o n of hydrogen. The presence of t h i s non-zero e l e c t r i c f i e l d gradient i n these l i q u i d c r y s t a l s was further substantiated by experiments in v o l v i n g a ser i e s of deuterated methanes as s o l u t e s . I n these experiments, dip o l a r and quadrupolar coupling constants were measured. In the t h e o r e t i c a l p r e d i c t i o n s of dipolar couplings, the i n t e r a c t i o n p o t e n t i a l which describes the o r i e n t a t i o n of methane i s of second order t e n s o r i a l form.--6 This o r i e n t a t i o n a l mechanism involves the i n t e r a c t i o n of some l i q u i d c r y s t a l mean f i e l d with the v i b r a t i o n a l l y induced anisotropy i n some solute property. This i n t e r a c t i o n r e s u l t s i n a coupling between v i b r a t i o n - r o t a t i o n i n the methane molecule which leads to a correct p r e d i c t i o n of a l l the dip o l a r couplings.-^ This c a l c u l a t i o n involved three adjustable parameters. I t was also shown that the deuteron quadrupolar couplings observed can be understood on the basis of the same v i b r a t i o n - r o t a t i o n mechanism.^ The c a l c u l a t i o n of these quadrupo- l a r couplings, however, involves two a d d i t i o n a l molecular properties: ( i ) the e l e c t r i c f i e l d gradient at the deuterium nucleus taken at equi l i b r i u m geometry, and ( i i ) the d e r i v a t i v e of t h i s f i e l d gradient with respect to the C-D bond s t r e t c h . - 12 - The second parameter was found to be l i q u i d c r y s t a l dependent. However, i f the e f f e c t of the e x t e r n a l f i e l d g r a d i e n t as e s t i m a t e d from D2 i s taken i n t o account , the v a r i a t i o n i n t h i s parameter w i t h l i q u i d c r y s t a l d i s a p p e a r s as i s expected f o r a m o l e c u l a r p r o p e r t y . T h i s s t r o n g l y suggests t h a t methane and hydrogen exper ience the same f i e l d g r a d i e n t . I n f u r t h e r experiments i n v o l v i n g hydrogen, the e x t e r n a l e l e c t r i c f i e l d g r a d i e n t was found to be of o p p o s i t e s i g n i n EBBA and 1132; and i t i s a f u n c t i o n o f weight c o m p o s i t i o n i n m i x t u r e s o f these two l i q u i d c r y s t a l s . I t was e x p e r i m e n t a l l y shown t h a t the average e x t e r n a l f i e l d g r a d i e n t exper ienced by a deuteron nuc leus i s zero i n a 55 wt% 1132 m i x t u r e of 1132-EBBA a t 301.4 ± 0.3 K . T h i s m i x t u r e i s u s e f u l because i t p r o v i d e s a system f o r s t u d y i n g o r i e n t a t i o n a l order where the mecha- nism due to the e l e c t r i c f i e l d g r a d i e n t i s no longer p r e s e n t . The order parameter o b t a i n e d from D2 i n t h i s mix ture was, however, not z e r o , but about 10% o f the magnitude observed i n each of the two component l i q u i d c r y s t a l s . T h i s s t r o n g l y i n d i c a t e s t h a t there i s an a d d i t i o n a l mechanism. I n a r e c e n t s tudy by van der E s t e t a l . , 2 2 a s e r i e s o f s m a l l molecules w i t h or h i g h e r symmetry were d i s s o l v e d i n EBBA, 1132 and a 55 wt% 1132 m i x t u r e . A model was proposed by van der E s t to d e s c r i b e the a d d i t i o n a l o r i e n t a t i o n a l mechanism. I n the m i x t u r e where D2 exper iences zero e f g , i t was assumed t h a t a l l the o ther s o l u t e s e x p e r i - ence the same zero e l e c t r i c f i e l d g r a d i e n t . The a d d i t i o n a l mechanism was proposed t o be a s h o r t range h a r d body i n t e r a c t i o n between the s o l u t e s and s o l v e n t . T h i s i n t e r a c t i o n i s dependent on the dimensions of the s o l u t e s . I t was shown t h a t order parameters c o u l d be p r e d i c t e d - 13 - quite accurately using t h i s model which i s based on the s i z e and shape of the solutes. The order parameters were also c a l c u l a t e d by using an i n t e r a c t i o n mechanism between the p o l a r i z a b i l i t y and the anisotropy of an e l e c t r i c f i e l d squared due to the l i q u i d c r y s t a l . Again, good agreement between t h e o r e t i c a l and experimental values was obtained, and t h i s i s not s u r p r i s i n g since the p o l a r i z a b i l i t y i s to a good approximation a func- t i o n of the s i z e and shape of the solute. In contrast the quadrupole moment i s a function of the e n t i r e e l e c t r o n i c structure and i s not ne c e s s a r i l y r e l a t e d to the size and shape of solutes. This suggests that i f the co n t r i b u t i o n to the order parameter from the e l e c t r i c f i e l d gradient-molecular quadrupole moment i n t e r a c t i o n i s removed, then any molecular property that i s r e l a t e d to the s i z e and shape can be used to pr e d i c t o r i e n t a t i o n s . In a sense, t h i s poses a problem i n that i t i s then d i f f i c u l t to d i s t i n g u i s h between the d i f f e r e n t mechanisms. I t i s expected that f o r large solutes, however, the short range hard body i n t e r a c t i o n has to play an important r o l e . Therefore, i t seems worth- while to investigate t h i s mechanism i n d e t a i l . In the component l i q u i d c r y s t a l s , where an efg i s present, two mechanisms, i . e . the e l e c t r i c f i e l d gradient-quadrupolar moment, and si z e and shape, were included i n the p r e d i c t i o n of order parameters. Again the parameters were quite accurately predicted. I t was therefore concluded that the o r i e n t a t i o n of solutes i n the l i q u i d c r y s t a l s can be described by these two mechanisms. The size and shape pi c t u r e proposed by van der Est models well one of the o r i e n t a t i o n a l mechanisms i n the ser i e s of C 3 molecules. - 14 - 1.2 Objectives of th i s Thesis The main o b j e c t i v e s of the work presented here are t w o - f o l d : ( i ) to s tudy f u r t h e r the s h o r t range h a r d body i n t e r a c t i o n s r e s p o n s i b l e f o r the o r i e n t a t i o n of s o l u t e s i n the l i q u i d c r y s t a l 55 wt% 1132, and ( i i ) to t e s t the e f f e c t i v e n e s s o f the s i z e and shape model which i s used i n the i n t e r p r e t a t i o n of the o r i e n t a t i o n a l order o f the s o l u t e s . For these purposes , a s e r i e s o f and molecules ( h e r e a f t e r r e f e r r e d to g e n e r a l l y as C 2 V ) were chosen f o r the s t u d y . Two order parameters are r e q u i r e d to d e s c r i b e f u l l y the o r i e n t a t i o n of each C 2 V * s o l u t e . I n C g v m o l e c u l e s , o n l y one parameter was i n v o l v e d . I t i s not c l e a r whether each s o l u t e i s o r i e n t e d i n e x a c t l y the same environment, hence comparison of order parameters of molecules i s not q u a n t i t a - St t i v e . For C 2 V m o l e c u l e s , q u a n t i t a t i v e comparison o f parameters can be made because the two parameters o f each s o l u t e d e s c r i b e o r i e n t a t i o n i n e x a c t l y the same environment . For t h i s reason , the s e r i e s of C 2 V molecules p r e s e n t s a more r i g o r o u s t e s t f o r the model . - 15 - CHAPTER I I THEORY - 16 - II . THEORY II.1 NMR of P a r t i a l l y Oriented Molecules The theory of the NMR spectra of oriented molecules has been discussed by several authors.9|23 The Hamiltonian H of a system of spin n u c l e i i n an i s o t r o p i c medium i s given by H - -S {l-oO i / i l z i + S J L i I±-I* [1] 1 K j J J where i s the chemical s h i f t of nucleus i i/£ i s the resonance frequency of the bare nucleus i A 1^ i s the spin angular momentum operator of nucleus i I z i i s the component of the spin angular momentum of nucleus i i n the Z-axis (of an external frame of reference). J ^ j i s the i s o t r o p i c i n d i r e c t nuclear spin-spin coupling constant between n u c l e i i and j The high r e s o l u t i o n NMR spectrum i s thus defined by the i s o t r o p i c chemical s h i f t s of the n u c l e i and the i n d i r e c t nuclear spin-spin coupling constants between n u c l e i within the same molecule. For a p a r t i a l l y aligned spin system with the d i r e c t o r of the nematic phase p a r a l l e l to the external magnetic f i e l d , the Hamiltonian - 17 - i s H -2 (1 - a i z z ) »/ i ZI z i + .E. n + ^ Dij (- I Z i I Z j - I i - I j ) + f — ( 3 I Z 1 ^2 - i ) :2] where D^j i s the d i r e c t spin-spin coupling between 2 spins i s the quadrupolar coupling constant of nucleus i aiZZ - s a v e r a g e ZZ component of the chemical s h i e l d i n g tensor The a n i s o t r o p i c s i n i n d i r e c t coupling constants can be neglected for protons. For n u c l e i of spin greater than i n a molecular f i x e d a x i a l l y symmetric e l e c t r i c f i e l d gradient, -eq, the quadrupolar coupling i s Be-qQi Bi = S £ [3] 4h where eQ^ i s the nuclear quadrupolar coupling constant S i i s the order parameter describing the average o r i e n t a t i o n of the d i r e c t i o n associated with the symmetry axis of the e l e c t r i c f i e l d gradient tensor at nucleus i . This equation applies f o r the case where i n t e r n a l and reorienta- t i o n a l motions are separable. The observed quadrupole s p l i t t i n g , how- - 18 - ever, contains an extra contribution from the external e l e c t r i c f i e l d gradient of the l i q u i d c r y s t a l . I t can be wr i t t e n i n the form: 3eQi Bobs - B i FZZ [*] 4h where Fzz i s the external e l e c t r i c f i e l d gradient present i n the l i q u i d c r y s t a l . The d i r e c t coupling D^j i s given by - n 7 i 7 i 3 COS^S^A - 1 Dij ± < i > [5] 4T T 2 2 r i j 3 where 0jj i s the angle between the magnetic f i e l d d i r e c t i o n (Z-axis of the external frame of reference) and the axis connecting the 2 n u c l e i i and j separated by a distance r j j 7£ i s the magnetogyric r a t i o of nucleus i the angle brackets denote that the measured D^j i s averaged over a l l intermolecular and intramolecular motions. h7i7j i s equal to 120.067 kHz A J f o r a p a i r of protons i f r ^ j i s measured i n A and D^j i n kHz. I f the intramolecular and intermolecular averages of equation [5] can be performed separately, one obtains - 19 - h7i7j -J 4 i r - 1 > S [6] w i t h the o r i e n t a t i o n parameter S^j (the degree o f o r i e n t a t i o n o f the a x i s p a s s i n g through i and j ) d e f i n e d as 3 c o s - f l y - 1 s i i = < > [7] J 2 The average o r i e n t a t i o n o f a r i g i d molecule o f a r b i t r a r y symmetry i n an a n i s o t r o p i c environment w i t h c y l i n d r i c a l symmetry about the Z - a x i s of the e x t e r n a l frame can be d e s c r i b e d by a 3x3 symmetric , t r a c e l e s s m a t r i x (S) w i t h 5 independent e lements . The m a t r i x elements are g i v e n by S p q - (V2) < 3 c o s ep c o s 8q " 5 p q > t 8 l where p , q are the axes of a c o o r d i n a t e system xyz f i x e d w i t h i n the m o l e c u l e . 0p i s the angle between the molecule p a x i s and the l a b f i x e d Z - a x i s . a a a A molecule f i x e d d i r e c t i o n a forming the angles a x , a v , az w i t h the m o l e c u l e - f i x e d xyz c o o r d i n a t e system has an S -va lue which i s r e l a t e d to the m a t r i x elements Spq by the f o l l o w i n g e q u a t i o n - 20 - S a - S cos a p cos aQ S p q [9] p,q v This shows that given s u f f i c i e n t S a values the matrix elements Spq may be obtained and thus the ordering matrix {S} f o r the molecule can be determined. Since {S} i s symmetric and t r a c e l e s s , the 5 independent elements are r e l a t e d as follows: Sxx + S y y + s z z *" 0 and spq - sqp p.q - x - y . 2 [ 1 Q ] For C 2 v molecules, the number of independent S-values necessary fo r the d e s c r i p t i o n of o r i e n t a t i o n can be reduced from f i v e to two by a s u i t a b l e choice of molecular axes. I f the C 2 axis i s selected as the z-axis, and i f x and y axes are chosen to be i n the 2 perpendicular planes p a r a l l e l to the z-axis, then S x v = S x z •= S v z = 0 and the two independent o r i e n t a t i o n parameters are S Z 2, and S x x-Syy. II.2 Size and Shape Model [Ref. 22; van der Est, (private comm.)'*] For a molecule i n an a x i a l l y symmetric environment, the components of the order parameter tensor can be c a l c u l a t e d c l a s s i c a l l y to be - 21 - S J (3 cos 0 p cos 6q - S p q ) exp ( - U ( f l ) / k B T ) dXi [11] pq 2 J exp ( -U (n) /k B T) dfi where the i n t e g r a t i o n i s over a l l o r i e n t a t i o n s fl = fl(0p, 0q) and U(fl) i s the mean p o t e n t i a l which d e s c r i b e s the i n t e r a c t i o n between the s o l u t e molecule and the l i q u i d c r y s t a l . U(fl) can be w r i t t e n as the sum of l o n g and s h o r t range i n t e r a c t i o n s where l o n g range i n t e r a c t i o n s i n v o l v e i n t e r m o l e c u l a r d i s t a n c e s which are much l a r g e r than the m o l e c u l a r d imensions ; and s h o r t range i n t e r a c t i o n s i n v o l v e those which are s h o r t e r than (or comparable to) the m o l e c u l a r d imens ions . The s h o r t range i n t e r a c t i o n c o n s i s t s of b o t h an a t t r a c t i v e and r e p u l s i v e p a r t as a f u n c t i o n o f the d i s t a n c e between the two i n t e r a c t i n g m o l e c u l e s . For s h o r t d i s t a n c e s , the a t t r a c t i v e p a r t i s i g n o r e d and the r e p u l s i v e p a r t becomes the dominant i n t e r a c t i o n . The l i q u i d c r y s t a l molecules are l a r g e and e x i s t i n many d i f f e r e n t c o n f o r m a t i o n s . An exact d e s c r i p t i o n o f the i n t e r a c t i o n between these l i q u i d c r y s t a l molecules and the s o l u t e s would be e x c e e d i n g l y c o m p l i - c a t e d . The approach taken i s to model the system i n a s imple but p h y s i c a l l y meaningful way. The l i q u i d c r y s t a l i s model led as an e l a s t i c tube p a r a l l e l to the f i e l d d i r e c t i o n . The s o l u t e s are assumed to be r i g i d and to f i t i n t o the system by s t r e t c h i n g the tube . The w a l l s of the tube are assumed to u(n) U S R ( ° ) + U L R W [12] - 22 - be r i g i d such that any displacement i s only i n the X-Y d i r e c t i o n , i . e . the energy to displace the wall i n the Z - d i r e c t i o n i s n e g l i g i b l e compared to the displacement energy i n the X-Y d i r e c t i o n . The stretched walls w i l l then remain p a r a l l e l to the Z-axis ( F i g . II.1). The poten- t i a l of the system i s then e f f e c t i v e l y the energy needed to displace the tube upon the introduction of the solutes into the system. This displacement leads to a r e s t o r i n g force which i s proportional to the deformation i n the X-Y d i r e c t i o n . 2TT F(fi) - -k J r(a,fj) da = -kc(fl) [13] o where r(a ,fi) i s the vector i n the X-Y plane from the o r i g i n to the tube surface. a i s the angle between the X-axis and r ( a , 0 ) . c(f i ) i s the circumference of the deformed tube, k i s the Hooke's law force constant. The p o t e n t i a l energy associated with the displacement of the l i q u i d c r y s t a l tube i n the X-Y d i r e c t i o n i s kc2(fl) U SR (0) - -S HO) dc(fi) - [14] 2 c(fl) i s dependent on the model chosen to describe the s i z e and Fig. II.1 Elastic tube model for the short range Interactions between solute and liquid crystal: The solute, represented by an array of van der Vaals spheres displaces the liq u i d crystals. The displaced volume is a tube with i t s wall parallel to the laboratory fixed Z-axis. 0 is the angle between the molecule and liquid crystal axes - 24 - shape of the solute molecules. This circumference i s also the surface of the e l a s t i c tube which i n t e r a c t s with the solute molecules. This surface acts as a boundary i n separating the molecules from a region which i s ina c c e s s i b l e to these solutes. The i n a c c e s s i b l e region i s not well-defined and as such the surface has to be c a l c u l a t e d d i f f e r e n t l y for each solute. To overcome t h i s d i f f i c u l t y , i t i s assumed that the surfaces of the e l a s t i c tube and the solute molecules are hard, so c(fi) i s taken to be the circumference of the projected molecule i n the X-Y plane. The solute molecule i s modelled as a c o l l e c t i o n of van der Waals spheres centred on f i x e d positions (x^.y^.z^) i n the molecular axis system. Each atom has a sphere of radius r ^ associated with i t , r ^ i s the van der Waals radius f o r the atom. The p r o j e c t i o n of the molecule from the molecule f i x e d axis onto the space f i x e d axis i s done by two rotations of the axis system. The f i r s t r o t a t i o n i s i n a counter- clockwise d i r e c t i o n through an angle 8 about the space f i x e d Y axis. This i s followed by a second r o t a t i o n i n a counter clockwise d i r e c t i o n through an angle <f> about the r e s u l t i n g z-axis. The coordinates of the i t n atom of the solute molecule i n the X-Y plane are given by X^ = x^ cos 6 cos <f> - y^ cos 8 s i n 4> + z^ s i n Y^ — x^ s i n 4> + y^ cos 4 [15] Thus the p r o j e c t i o n of the molecule i n the X-Y plane i s an array of overlapping c i r c l e s centred at (X^, Y^) (Fig. II.2.A). The i t n projected c i r c l e can be described by - 25 - ( X - X i ) 2 + ( Y - Y i ) 2 - Vi2 The maximum and minimum values of X and Y of the i t n projected atom are given by Xmax^ = X i + r i Xmin^ = X i - r i Ymax^ " Y i + r i Ymin^ = Y i - r i I f Xmin^ and Yminj are the smallest, and Xmax^ and YmaXjj are the largest of the coordinates, then the points (Xmax^, Y^), (Xmin^, Y^), (Xj, Yminj) and (XJJJ, YmaXjjj) l i e on the outer surface of the projected c i r c l e s . The perimeter of the projected molecule i s determined using the minimum circumference of the array of the overlapping c i r c l e s , which i s defined i n the same manner f o r a l l solute molecules (Fig. II.2.B). U(fi) can then be c a l c u l a t e d from equation [14] using c(fl). The order parameters can then be obtained by an in t e g r a t i o n of equation [11] over a l l o r i e n t a t i o n s of the solute. For molecules with symmetry C2 V*, there are two independent parameters S Z 2 and S x x. In terms of the model, - 26 - 7T 2TT S z z = f 0 / 0 (3 cos 2 6 - 1) exp {(-kc 2(0 ,^)/2kBT) sin 6 d8d(f> n ir/2 2SoIo e x P t -kc2(0,tf)/2kBT} sin 8 dd d<f> JT 2TT S x x = J 0 J 0 (3 s i n 2 8 cos 2 ^ - 1) exp {(-kc 2(0 ,«£)/2kBT) sin 8 d8d<f> w n/2 2J"oJo e x P ( -kc2(0,^)/2kBT} sin 8 d8 d<f> [17] The single parameter of the model, the force constant k, is obtained by a least squares procedure where there was optimal agreement between the theoretical and the experimental order parameters of the series of solutes in the same liquid crystal. - 27 - t r / l o i \ X / i / / - „ ' Fig. II.2 Projection of solute in X-Y plane: A : r is • vector from the origin to the surface of the pro- jected molecule and a is the angle between r and the x-axis. i / V • / A / ' %/ ' ' / ^^^^^^ / \ - -V ' \ \ 1 > Y 1  > \ V ' \ N ' \ _ " V / / / 1 1 ^^^^^^ \ / 'A Fig. II.2 Projection of solute in X-Y plane: B: The minimum circumference of the elastic tube represent ing the deformation of the liquid crystal solvent by a solute at some orientation is shown In bold face. - 28 - CHAPTER I I I EXPERIMENTAL - 29 - I I I . EXPERIMENTAL The l i q u i d c rystals used were deuterated EBBA: N-(4-ethoxybenzyli- dene)-2,6-dideutero-4-n-butylaniline and 1132: Merck ZLI 1132. The compounds l i s t e d i n Table IV.1 were purchased from a variety of chemical suppliers. These compounds and 1132 were used without further p u r i f i - cation. The composition of 1132 i s given as follows :̂ -> Merck L i c r y s t a l ZLI 1132: 24% C 1 6H 2 1N (I) 36% C 1 8H 2 5N ( I D 25% C20 H29 N ( I I I ) 15% C 2 4 H 2 9 N (IV) where I : R x - C 3H 7 I I : R l " C 5 H n I I I : R x - C 7H 1 5 R 2 R 2 R 2 Ph-ON Ph-ON Ph-ON IV : R x - C 5H 1 : L ON The deuterated EBBA was synthesized as i n Section I I I . l . and III.2 . - 30 - I I I . l Deuteration of A-n-butylaniline The selective deuteration of 4-n-butylaniline at two ring positions is as illustrated below:-*6 4-n-Butylaniline was f i r s t purified by vacuum d i s t i l l a t i o n to give a clear liquid. 100 g of this was then added dropwise to -350 ml of 2M HC1. The amine salt that formed was soluble i n water, and gave a yellowish o i l y solution. Water was removed by evaporation. This was followed by the addition of -100 ml D20 to dissolve the salt. The mixture was then refluxed for 3 hours to deuterate the two ring posi- tions. The excess acid was then neutralized with KOH. N.N,2,6-tetra- deutero-4-n-butylaniline was extracted with ether and further purified by vacuum d i s t i l l a t i o n . - 31 - III.2 Preparation of EBBA EBBA was prepared by the r e a c t i o n as i l l u s t r a t e d below: 60 g o f deuterated 4 - n - b u t y l a n i l i n e , 60 g of 4-ethoxybenzaldehyde (both p u r i f i e d by vacuum d i s t i l l a t i o n ) , and 0.75 g of 4 - t o l u e n e s u l f o n i c a c i d were d i s s o l v e d i n 600 ml of toluene and r e f l u x e d f o r 4 hours. The water formed d u r i n g the r e a c t i o n was removed a z e o t r o p i c a l l y by means of a Dean Stark apparatus. At the end of the r e a c t i o n , toluene was removed by evaporation to y i e l d a dark brown l i q u i d . The compound was r e c r y s - t a l l i z e d from methanol u n t i l constant phase t r a n s i t i o n temperatures were obtained. The pale y e l l o w f l a k y c r y s t a l s of EBBA were l e f t to dry under vacuum overnight. T r a n s i t i o n p o i n t s obtained f o r the p u r i f i e d EBBA were: 308 ± IK and 351 ± IK. These temperatures agree w e l l w i t h the - 32 - l i t e r a t u r e v a l u e s * . 2 8 308K 352K C r y s t a l s > Nematic Phase > I s o t r o p i c Phase (308K)* (351K)* The deuteron NMR spectrum o f EBBA showed two double t s o f l i n e w i d t h 600 Hz and s p l i t t i n g s o f 22 and 19 k H z . The h i g h r e s o l u t i o n p r o t o n NMR spectrum showed t h a t the compound i s p u r e . I I I . 3 Preparation of 55 wt% 1132 mixture 13.5 g o f EBBA and 16.5 g o f 1132 i n a 50 ml Erlenmeyer f l a s k were mixed by h e a t i n g the mix ture to the i s o t r o p i c phase and v o r t e x i n g i t . T h i s process was repeated s e v e r a l t i m e s . The mix ture was s t o r e d under n i t r o g e n and i n the dark to prevent any d e g r a d a t i o n o f the compounds. A h i g h p r e s s u r e sample o f D 2 i n t h i s m i x t u r e was made up (see S e c t i o n I I I . 4 ) to check the magnitude o f the average e l e c t r i c f i e l d g r a d i e n t . F z z was found to be 0.227 ± 0.79 x 1 0 1 0 esu i n t h i s 55 wt % 1132 m i x t u r e o f 1132-EBBA at 301.4 K (see S e c t i o n I I I . 5 ) . T h i s v a l u e i s zero w i t h i n the e r r o r l i m i t s . I I I . 4 Preparation of NMR Samples The 55 wt % 1132 m i x t u r e of 1132-EBBA l i q u i d c r y s t a l i n 5 mm sample - 33 - tubes was f i r s t t h o r o u g h l y degassed by the freeze-pump-thaw method. For s o l u t e s which are l i q u i d s or s o l i d s , a s u f f i c i e n t amount o f the compound was added to the l i q u i d c r y s t a l m i x t u r e to produce a c o n c e n t r a t i o n of 1 mole p e r c e n t . The tubes were then capped and t h o r o u g h l y mixed by v o r t e x i n g the samples i n the i s o t r o p i c phase. Samples o f f u r a n and thiophene i n 1132 and EBBA were made up i n a s i m i l a r manner. For the D 2 sample, a s u f f i c i e n t volume o f the gas to produce a p r e s s u r e o f 25 atm under STP c o n d i t i o n s was condensed i n t o the l i q u i d c r y s t a l m i x t u r e i n a c o n s t r i c t e d 9 mm tube c o o l e d i n l i q u i d h e l i u m . The tube was then s e a l e d and p r e s s u r e t e s t e d i n an oven a t about 425 K. A l l samples were s t o r e d i n the dark to prevent d e g r a d a t i o n of EBBA. I I I . 5 NMR Spectroscopy P r o t o n and deuteron s p e c t r a were o b t a i n e d u s i n g F o u r i e r Transform techniques w i t h a Bruker WH-400 NMR spectrometer equipped w i t h an Oxford Instruments 9.4T superconduct ing magnet, o p e r a t i n g a t 400.1 MHz f o r p r o t o n s and 61.4 MHz f o r deuterons . The deuteron s i g n a l of the deuter - a t e d EBBA was observed through the l o c k channel thus e n s u r i n g i d e n t i c a l c o n d i t i o n s . The temperature was c o n t r o l l e d by means of a v a r i a b l e temperature gas f l o w u n i t and c a l i b r a t e d u s i n g the p r o t o n chemica l s h i f t d i f f e r e n c e s from a sample of e thy lene g l y c o l . The d i a l temperature of 304 K was c a l i b r a t e d to 301.4 ± 0.3 K. Other temperatures were not c o r r e c t e d . A l l samples were heated up to the i s o t r o p i c phase and v o r t e x e d b e f o r e b e i n g p l a c e d i n the probe . Samples were u s u a l l y l e f t to - 34 - e q u i l i b r a t e f o r h a l f an hour b e f o r e nmr s p e c t r a l a c q u i s i t i o n . A l l experiments were done w i t h o u t f i e l d f requency l o c k . I t was t h e r e f o r e impor tant to o b t a i n the s p e c t r a i n the s h o r t e s t t ime p o s s i b l e to coun- t e r a c t magnetic f i e l d d r i f t and s l i g h t temperature f l u c t u a t i o n s . A p u l s e w i d t h of 12 ^ s w a s used f o r a l l the p r o t o n exper iments . The number o f scans used v a r i e d from 8 to 32 and the l i n e w i d t h was i n the range of 2-10 Hz depending on the samples. For the deuteron s p e c t r a , a p u l s e w i d t h o f 10 ;us and a r e l a x a t i o n d e l a y o f 0.3 s were used . A thousand scans were necessary to o b t a i n a good s i g n a l to n o i s e spectrum. Solutes i n 55 wt % 1132 - The s p e c t r a o f a l l the s o l u t e s i n 55 wt% 1132 were o b t a i n e d a t 301.4 K ( d i a l T = 304 K ) . For each sample, a p r o t o n spectrum of the s o l u t e and a deuteron spectrum o f the l i q u i d c r y s t a l were c o l l e c t e d . D2 i n 55 wt % 1132 - Deuteron s p e c t r a o f both the s o l u t e and the d e u t e r a t e d EBBA were o b t a i n e d a t v a r i o u s temperatures between 304-325 K ( d i a l T ) . Furan and thiophene - Samples of f u r a n and thiophene i n 55 wt % 1132 m i x t u r e were a l s o s t u d i e d as a f u n c t i o n of temperature r a n g i n g from 304-325 K ( d i a l T ) . A t h i g h e r temperatures , the presence o f temperature g r a d i e n t s a l o n g the sample tube caused l i n e broadening i n the s p e c t r a . T h i s c o u l d be s l i g h t l y reduced by i n c r e a s i n g the a i r f l o w o f the h e a t e r . P r o t o n s p e c t r a o f f u r a n and of thiophene i n the l i q u i d c r y s t a l s 1132 and - 35 - EBBA were c o l l e c t e d at 301.4 K. III.6 Spectral Analysis Proton spectra of solutes - The proton spectra obtained were then analyzed using the i t e r a t i v e programs LEQU0R-9 and SHAPE. -"0 For each compound, a set of s t a r t i n g parameters of chemical s h i f t s , i n d i r e c t coupling constants, order parameters and an appropriate geometry from el e c t r o n d i f f r a c t i o n or microwave studies, were fed into the program LEQUOR. I t e r a t i v e assignment procedures were used u n t i l a l l the peaks i n the c a l c u l a t e d spectrum were assigned and the root mean square (rms) erro r between c a l c u l a t e d and experimental peaks was of the order of the d i g i t a l r e s o l u t i o n of the experimental spectrum. The anisotropic chemical s h i f t s , i n d i r e c t coupling constants and dip o l a r coupling constants, ) were obtained from the f i n a l s p e c t r a l c a l c u l a t i o n s . The D^j values were then used as input into the program SHAPE to give the molecular order parameters Spq as well as a r e f i n e d geometry. Deuteron spectra of D 2 i n 55 wt % 1132 - The deuteron NMR spectrum i s as shown i n F i g . I I I . l . The s p e c t r a l analysis y i e l d e d values of and Djj . The value of D^j , i n conjunction with the v i b r a t i o n a l l y averaged value of r " 3 , was then used to obtain the value of the order parameter from equation [6]. An experimental value of the e l e c t r i c f i e l d gradient, F-;z> was then obtained from equation [4].  - 37 - Deuteron spectra of deuterated EBBA - The quadrupolar s p l i t t i n g s of the deuterated EBBA were obtained by measuring the distance (Hz) between the two doublets. - 38 - CHAPTER IV RESULTS - 39 - I V . RESULTS I V . 1 S o l u t e s i n 55 wt% 1132 m i x t u r e at 301.4K Examples o f the h i g h r e s o l u t i o n p r o t o n NMR s p e c t r a o f a s o l u t e d i s s o l v e d i n the nematic l i q u i d c r y s t a l 55 wt% 1132 m i x t u r e are as shown i n F i g s . I V . 1 . A and I V . 2 . A . F i g . I V . 1 . A i s the spectrum of 1 ,4 -d ibromo- benzene i n the l i q u i d c r y s t a l m i x t u r e . I t has a l i n e w i d t h o f 5 H z , s p e c t r a l w i d t h o f -9 ,000 Hz and c o n s i s t s o f twelve peaks . The spectrum i s s imple and symmetr i ca l because the molecule i s a f o u r s p i n A A ' A ' ' A ' ' ' system. F i g . I V . 2 . A i s the spectrum o f p a r t i a l l y o r i e n t e d f luorobenzene w i t h a l i n e w i d t h o f 2 H z , s p e c t r a l w i d t h o f 3500 Hz and has over seventy peaks . S ince the molecule i s a s i x s p i n A A ' B B ' C X system, the r e s u l t i n g spectrum i s c o m p l i c a t e d . An example of the deuteron spectrum of d e u t e r a t e d EBBA i n the 55 wt% 1132 i s as g i v e n i n F i g . I V . 3 . The quadrupolar s p l i t t i n g s of the o u t e r and i n n e r double t s are about 19 and 16 kHz r e s p e c t i v e l y , and the l i n e w i d t h i s about 600 H z . The e x p e r i m e n t a l p r o t o n s p e c t r a were a n a l y z e d u s i n g the program LEQUOR as d e s c r i b e d e a r l i e r ( S e c t i o n I I I . 6 ) . The s p e c t r a s i m u l a t e d by t h i s program are shown i n F i g s . I V . I . B and I V . 2 . B . From the s p e c t r a l a n a l y s e s , d i r e c t d i p o l a r c o u p l i n g c o n s t a n t s , i n d i r e c t c o u p l i n g c o n s t a n t s , chemica l s h i f t d i f f e r e n c e s and the rms e r r o r s o f the f i t s were o b t a i n e d and these are summarized i n Table I V . 1 . - 40 - (A) (B) i 1 ; : i : : 1 -S95 00 - 5 4 0 . 5 5 - 3 8 6 I I - 2 3 1 . 6 7 - 7 7 2 2 7 7 . 7 2 2 3 1 . 6 7 3 B 6 I I -10' F r e q u e n c y (Hz ) Fig. IV.1 Proton NMR spectrum of 1,4-dibromobenzene par t i a l l y oriented in 55 wt% 1132: (A) experimental (B) computer simulation. Temperature - 301.4 K. Concentration « 1 mole %. Spectrometer Frequency - 400 MHz. (B) i 1 1 1 — - — — i 1 , 1 ••846 61 -769 71 -692 82 -615.92 -539 03 -462.14 -3B5 24 -308 35 .10' F r e q u e n c y ( H z . ) Fig. IV.2 Proton NMR spectrum of fluorobenzene pa r t i a l l y oriented 55 wt% 1132: (A) experimental (B) computer simulation. Temperature •* 301.4 K. Concentration - 1 mole %. Spectrometer Frequency - 400 MHz. Fig. IV.3 Deuteron NMR spectrum of deuterated EBBA at 301.4 K - 43 - Table IV.1: Experimental dipolar couplings* (Hz), Indirect couplings** (Hz), chemical shift differences (Hz), and the rms errors 0 (Hz) obtained from the program LEQDOR for solutes dissolved in the nematic liquid crystal 55 vt% 1132 at 301.4 K. Molecule Parameter References-1 1 TTF D 1 2 (tetrathiofulvalene) D 1 3 H 3 V / \ / \ H 2 D 1 4 C = C3 |J rms -674.42 (5) e 68.95 (6) 90.06 (6) 8.00 0.20 31 Acetone H /H. 2v i 1 H. H i > = 0 Furan D 1 2 Dl4 ^14 rms D 1 2 D 1 3 I>14 D23 J 1 2 ^13 ->14 J23 v2-v\ rms 569.48 (3) -171.68 (3) 0.55 0.36 -292.80 (4) -110.91 (4) -158.85 (4) -524.61 (5) 1.75 0.81 1.48 3.27 371.56 (9) 0.13 32 33 - 44 - Thiophene D 12 -549.56 (5) D 1 3 - 99.16 (6) I>14 - 75.22 (10) D 2 3 -379.93 (9) J 1 2 4.90 J 1 3 1.04 J 1 4 2.84 J 2 3 3.50 v2'vl 84.80 (15) rms 0.21 D 1 2 -368.7 (4) D 1 3 - 93.7 (A) »14 - 96.6 (4) Dl5 -189.2 (6) I>23 -703.4 (3) D 2 4 -164.8 (8) Jl2 4 .86 J l 3 1.85 J l 4 0.98 J l 5 -0 .13 J 2 3 7.66 J 2 4 1.36 V2-vi 539 (1) ^ 2 - i / 3 103 (1) rms 1.3 - 45 - 2 , 6 - D i f l u o r o p y r i d i n e Fluorobenzene D 1 2 -247 .77 (11) D 1 3 - 84 .35 (11) »14 -103 .84 (10) Dl5 -179 .2 (3) D 2 3 -903 .66 (6) D 24 -222 .50 (16) J 1 2 - 2 .47 J 1 3 7 .97 J l 4 1 .19 J l 5 - 12 .23 J 2 3 7 .94 J 2 4 0, .55 t , 2 - i / 3 404. .5 (3) rms 0. .42 D 1 2 -509. ,84 (7) D 1 3 -148. 78 (7) D 14 -113. 33 (4) D 2 3 -1067. 95 (3) D 24 -176. 05 (5) D 25 - 71. 60 (3) D 26 - 76. 30 (5) D 34 -562. 49 (5) D 3 5 - 75. 67 (5) J 1 2 8. 90 J 1 3 5. 57 - 46 - Chlorobenzene CI J 1 4 0.20 J 2 3 8.35 J24 1.03 J 2 5 0.40 J26 2.58 J34 7.50 J 3 5 1.76 i/2 -1/3 87.9 (1) 63.9 (1) rms 0.22 D 1 2 -1578.04 (9) D 1 3 -232.1 (3) °14 - 55.29 (9) »15 - 10.4 (5) D 2 3 -430.7 (3) D24 - 10.5 (5) J12 8.15 J 1 3 1.14 J l 4 0.50 J 1 5 2.24 J 2 3 7.57 J24 1.71 " 2 - " l 8 (1) i / 2 - i / 3 100.1 (5) rms 0.49 - 47 - lodobenzene I 1,2-Dichlorobenzene C l D 1 2 -1886.73 (12) D 1 3 -260 (1) D 1 A - 39.82 (13) D 1 5 39 (3) D 2 3 -312 (1) D24 38 (3) J l 2 7.93 J l 3 1.12 ^14 0.47 J l 5 1.88 ^23 7.50 ^24 1.74 »2'vl 52 (7) t'2-»/3 232 (4) rms 0 .69 D12 -1060 .41 (6) D 1 3 -135 .72 (8) D14 - 66 .27 (16) D23 -508, .42 (16) J12 8. 06 J 1 3 1. 54 J l 4 0. 31 J 2 3 7. 48 vl'v2 59. 7 (3) rms 0. 29 - 48 - 1,2-Dicyanobenzene 1,3-Dichlorobenzene 1,3-Dinitrobenzene D 1 2 -1213.22 (17) D 1 3 -144.65 (19) D14 " 64.9 (4) D 2 3 -499.7 (4) J l 2 7.90 J l 3 1.26 J l 4 0.61 J 2 3 7.81 v2'vl 8 7 ( D rms 0.64 D 1 2 -107.00 (9) D 1 3 - 28.12 (14) D 2 3 -1207.88 (7) D 2 4 -296.89 (17) J l 2 1.97 J l 3 0.36 J 2 3 8.10 J 2 4 0.89 v^-V2 261.0 (3) vi-u^ 186.7 (3) rms 0.37 D 1 2 -133.6 (6) D 1 3 - 38 (1) D 2 3 -1431.0 (4) . 49 - H 3 1,4-Dichlorobenzene C l 1,4-Dibromobenzene Br D24 -355 (1) J 1 2 2 .20 J l 3 0 .50 J 2 3 8 .30 J24 2 .00 531 (2) vl' v\ 443 (2) rms 1 .90 D12 -2419 .38 (10) D13 - 25 .43 (13) *>14 -107 .04 (13) J 1 2 8 .55 J l 3 0. .39 J14 2. .58 rms 0. .44 D 1 2 -2727. 87 (10) D 1 3 - 12. 34 (12) »14 -150. 86 (11) J12 8. 41 J 1 3 0. 46 J l 4 2. 38 rms 0. 40 - 50 - The numbering of the protons i s as shown i n the drawings. I n d i r e c t c o u p l i n g constants were obtained from the l i t e r a t u r e . This i s the rms e r r o r of the f i t of the experimental s p e c t r a to the c a l c u l a t e d s p e c t r a by the program LEQUOR. References f o r i n d i r e c t c o u p l i n g constants. Numbers i n brackets r e f e r to e r r o r s , e.g. -2419.38(10) means -2419.38 ± 0.10. - 51 - The geometry o f the molecules t h a t were used i n the LEQUOR, and s i z e and shape programs are as presented i n Table I V . 2 . The i n p u t c o o r d i n a t e s o f the atoms o f iodobenzene, ch lorobenzene , 1 , 2 - d i c h l o r o - benzene, 1 , 3 - d i c h l o r o b e n z e n e , 1 ,2 -dicyanobenzene , 1 , 3 - d i n i t r o b e n z e n e and 2 , 6 - d i - f l u o r o p y r i d i n e were c a l c u l a t e d u s i n g data from the l i t e r a t u r e . For iodobenzene, the c a l c u l a t i o n s o f the atomic p o s i t i o n s were based on the assumption t h a t i t i s a r e g u l a r hexagon. C a l c u l a t i o n s o f 1 , 3 - d i - n i t r o b e n z e n e i n v o l v e d u s i n g a geometry from e l e c t r o n d i f f r a c t i o n s t u d i e s , and f o r 1 ,2-dicyanobenzene u s i n g t h a t from a l i q u i d c r y s t a l NMR s t u d y . The atomic c o o r d i n a t e s o f 2 , 6 - d i f l u o r o p y r i d i n e , ch lorobenzene , 1 , 2 - d i c h l o r o b e n z e n e , and 1 , 3 - d i c h l o r o b e n z e n e were c a l c u l a t e d from m i c r o - wave d a t a . R e s u l t s o f the a n a l y s i s from the program SHAPE: the se t o f e x p e r i - mental o r d e r parameters S x x , Syy and S z z , and the r e l a t i v e geometry as determined from the d i p o l a r c o u p l i n g s o f the s o l u t e s d i s s o l v e d i n 55 wt% 1132 are as l i s t e d i n Tables I V . 3 and I V . 2 r e s p e c t i v e l y . For acetone, a m o d i f i e d v e r s i o n of SHAPE was used to o b t a i n the order parameters . The m o d i f i e d program takes i n t o account the r o t a t i o n o f the methyl groups. The p r e d i c t e d order parameters were o b t a i n e d by i n t e g r a t i n g equa- t i o n s [17] u s i n g the s i z e and shape program w i t h the geometry o f the molecules (Table I V . 2 ) as i n p u t . The v a l u e s of S c a l c u l a t e d as g i v e n i n Table I V . 3 are accurate to f o u r f i g u r e s . The v a l u e o f k = 5.2 dyne/cm has been determined by a l e a s t squares f i t o f c a l c u l a t e d and e x p e r i - mental S. The r e l a t i v e i n t e r n u c l e a r d i s t a n c e s o f a molecule are determined u s i n g e q u a t i o n [ 6 ] . From Table I V . 2 i t i s noted t h a t the output c o o r d i - - 52 - nates t h a t were v a r i e d agree to w i t h i n ± 0.03 A w i t h the values from the l i t e r a t u r e except f o r TTF and 1,3-dinitrobenzene. The d i s c r e p a n c i e s observed i n these two molecules may be due to one of the d i p o l a r c o u p l i n g s being not a c c u r a t e l y determined and of a small magnitude. The r e l a t i v e i n t e r n u c l e a r distance r a t i o s c a l c u l a t e d u s i n g t h i s c o u p l i n g are then imprecise. - 53 - Table IV.2: Y •» X The geometry of the molecules (I) l i t e r a t u r e 3 ( i i ) experimental*5 - presented In brackets. The axis system for a l l the molecules is as shown here. The z-axis points out from the page. Molecules Atomc Coordinates (A) Y Z Radius d Ref. TTF Acetone 9 = 0 3 Furan c l 3.1930 -0.6572 -0 3743 1 75 c 3 0.6745 0 0 1 75 S i 1.6250 1.4777 0 1 75 H l -3.9975 1.2151 0 6640 1 20 (-3.811(7)) (1.2151) (0 6640) C l 0 0 0 1 69 c 2 -0.7700 1.3337 0 1 70 0 1.2220 0 0 1 50 H l -1.3968 1.3919 0 8898 1 20 H 2 -0.0621 2.1625 0 1 20 H 3 -1.3968 1.3919 -0 8898 1 20 C l 1.0920 0 0 1 77 c 2 0.7160 1.3080 0 1 77 0 0 -0.8140 0 1 50 Hi 2.0466 -0.8132 0 1 00 (2.0466) (-0.8132) (0) H 2 1.3777 1.8376 0 1 00 (1.3743(1)) (1.8119(17)) (0) 31 45 4 6 - 54 - Thiophene 2,6-Difluoro- pyridine c l 1.2360 0.0463 0 1 .77 c 2 0.7116 1.3121 0 1 .77 s 0 -1.1426 0 1 .75 H l 2.2692 -0.2550 0 1 .00 (2.2692) (-0.2550) (0) H 2 1.3201 2.2050 0 1 00 (1.3226(6)) (2.2341(4)) (0) 1.1416 -0.6929 0 1 77 c 2 1.1974 0.7005 0 1 77 c 3 0 1.4151 0 1 77 N 0 -1.3949 0 1 55 «1 2.0557 -1.2761 0 1 01 (2.054(3)) (-1.245(9)) (0) H 2 2.1526 1.2055 0 1. 01 (2.1526) (1.2055) (0) H 3 0 2.4924 0 1 01 (0) (2.4924) (0) Cl 1.1110 0.7080 0 1. 77 c 2 1.2070 2.0810 0 1. 77 c 3 0 2.7800 0 1. 77 N 0 0 0 1. 56 F l 2.2430 -0.0220 0 1. 47 (2.2430) (-0.220) (0) 47 48 from 49 7 Fluorobenzene F 8 Chlorobenzene - 55 - H 2 2.1710 2. ,5680 0 1. ,01 (2.1779(10)) (2. .5629(5)) (0) »3 0 3, .8620 0 1. .01 (0) (3. .8620) (0) C l 0 -0. .8490 0 1. .77 c 2 1.2170 -0. .1930 0 1. .77 c 3 1.2080 1. .2020 0 1. .77 C4 0 1. .9030 0 1. .77 F 0 -2. .2030 0 1. .47 (0) (-2, .2030) (0) H 2 2.1370 -0. .7610) 0 1. .01 (2.1501(6)) (-0. .7616(4)) (0) H 3 2.1460 1, .7430 0 1. .01 (2.1644(6)) (1. .7437(4)) (0) H A 0 2. .9830 0 1. .01 (0) (2. ,9830) (0) Cl 0 1. ,4002 0 1. ,77 c 2 1.2126 -0. ,7001 0 1. ,77 Cl 0 -3. 1112 0 1. ,77 Hi 2.1400 -0. ,2830 0 1. ,01 (2.109(2)) (-0. .2823(12)) (0) H 2 2.1454 2, .1817 0 1. .01 (2.1454) (2. .1817) (0) - 56 - 10 1,2-Dichloro- benzene 11 1,2-Dicyano- benzene H 3 0 3.4260 0 1. .01 (0) (3.4260) (0) c l 0 1.3970 0 1. .77 c 2 1.2098 -0.6985 0 1. .77 I 0 -3.4770 0 2. .06 Hi 2.1486 1.2405 0 1. .01 (2.1486) (1.2405) (0) H 2 2.1486 -1.2405 0 1. .01 (2.170(2)) (-1.237(3)) (0) H 3 0 -2.4810 0 1. .01 (0) (-2.4810) (0) c l 0.6985 -1.2098 0 1. .77 c 2 1.3970 0 0 1. .77 C l ! 1.5338 -2.7168 0 1 .77 Hi 2.4810 0 0 1. .01 (2.4520(17 )) (0) (0) H 2 1.2405 2.1846 0 1. .01 (1.2405) (2.1846) (0) Cl 1.4420 -3.6530 0 1. .78 C 2 0.7035 -2.4191 0 1. .77 c 3 1.4165 -1.2043 0 1. .77 CA 0.6955 0 0 1. ,77 »1 2.0318 -4.5933 0 1. .70 assumed regular hexagon 52 c a l c u l a t e d from 53 calculated from 40 - 57 - 1, 3-Dinitro- benzene "I 2.4803 -1 .2043 0 1 .01 (2.45(14)) (-1 .24(9)) (0) H 2 1.2388 0 .9334 0 1 .01 (1.2388) (0 .9334) (0) C l 0 1 .3960 0 1 .77 c 2 -1.2090 -0 .6980 0 1 .77 2.6906 1 .5638 0 1 .77 Hi 0 2 .4800 0 1 .01 (0) (2.4800) (0) H 2 -2.1480 -1 .2400 0 1 .01 (-2.1470(17)) (-1.2356(6)) (0) H 3 0 2 .4800 0 1 .01 (0) (2 .4800) (0) C l 0 0 .699 0 1, .77 c 2 -1.870 0 0 1 .77 c 3 -1.307 -1 .373 0 1, .77 C4 0 -2 .152 0 1. .77 N l 2.428 0. .763 0 1. .55 °1 3.435 0, .207 0, .425 1. .40 o 2 2.386 1. .912 -0. .425 1. ,40 Hi 0 1. .789 0 1. ,01 (0) (1. ,789) (0) H 2 -2.2920 -1. 839 0 1. 01 (-2.170(9)) (-1. 996(3)) (0) calculated from 54 calc u l a t e d from 55,56 - 58 - 14 1,4-Dichloro- benzene Cl 15 1,4-Dibromo- benzene Br H 3 0 -3.242 0 1. .01 (0) (-3.242) C l 0 -1.375 0 1, .77 43 c 2 1.213 -0.697 0 1. .77 C l i 0 -3.105 0 1. .77 " l 2.162 1.253 0 1. .01 (2.162) (1.255(1)) (0) C l 0 -1.375 0 1. .77 44 c 2 1.213 -0.697 0 1. 77 B r i 0 -3.215 0 1. ,92 H i 2.170 -1.252 0 1. 01 (2.165(1)) (-1.252) (0) These coordinates were used as input i n t o the programs LEQUOR, and s i z e and shape. These proton coordinates were determined from d i p o l a r couplings of the s o l u t e s d i s s o l v e d i n 55 wt % 1132. The numbers are presented i n br a c k e t s , e.g. (-3.8106(12)) where (12) i s the u n c e r t a i n t y i n the l a s t two decimal p l a c e s . The coordinates w i t h e r r o r s were v a r i e d during the c a l c u l a t i o n u s i n g SHAPE. The coordinates without e r r o r s were f i x e d as s c a l i n g f a c t o r s during c a l c u l a t i o n . Coordinates not shown are f i x e d by symmetry. ^ The values of r a d i i were taken from Ref. 57. c 59 - Table IV.3: Experimental and calculated order parameters of solutes dissolved in the nematic liquid crystal of 55 wt% 1132 mixture at 301.4 K M o l e c u l e a Order Parameter E x p e r i m e n t a l 0 C a l c u l a t e d 0 1 TTF 'xx yy 'zz 0.3320 (17) •0.081 (3) -0.2514 (17) 0.3859 •0.1402 -0.2457 2 Acetone ' x x yy zz 0.0090 (1) 0.0711 (2) •0.0720 (1) -0.0031 0.0712 •0.0681 3 Furan 'xx 'yy 'zz 0.0907 (1) -0.0458 (2) -0.1365 (1) 0.0602 0.0247 •0.0849 4 Thiophene ' x x yy 'zz 0.0586 (1) 0.0905 (5) •0.1490 (4) 0.0519 0.0428 •0.0947 5 P y r i d i n e 'xx yy 'zz 0.1093 (2) 0.0452 (6) •0.1545 (4) 0.0690 0.0394 •0.1084 - 60 - 2 , 6 - D i f l u o r o - p y r i d i n e yy ' z z 0.1529 (2) 0.0379 (4) -0.1908 (2) 0.1165 0.0266 -0.1431 Fluorobenzene 'xx yy ' zz 0.0507 (1) 0.1399 (2) -0.1906 (1) 0.0236 0.1081 -0.1317 Chlorobenzene 'xx yy ' z z 0.0070 (1) 0.1967 (3) -0.2037 (2) -0.0092 0.1520 -0.1428 lodobenzene 'xx yy ' z z •0.0243 (5) 0.2389 (11) •0.2146 (6) •0.0547 0.2196 •0.1649 1 , 2 - D ich lorobenzene S xx yy ' z z 0.0647 (1) 0.1601 (2) -0.2248 (3) 0.0254 0.1419 -0.1673 1,2-Dicyanobenzene S x x s y y s z z 0.063 (11) 0.184 (24) -0.247 (13) 0.0277 0.1729 -0.2006 - 61 - 12 1 , 3 - D ich lorobenzene S x x s y y s z z 0.1958 (4) 0.0285 (7) •0.2243 (3) 0.1916 •0.0134 -0.1782 13 1 , 3 - D i n i t r o b e n z e n e S x x Syy s z z 0.242 (3) 0.040 (4) •0.282 (1) 0.2092 •0.0092 •0.2000 14 1 , 4 - D i c h l o r o b e n z e n e S x x Syy s z z -0.0721 (1) 0.3188 (5) -0.2467 (4) -0.0976 0.2879 -0.1903 15 1,4-Dibromobenzene S xx ' y y ' z z -0.1021 (1) 0.3567 (2) -0.2546 (1) -0.1331 0.3395 -0.2064 The m o l e c u l a r a x i s system of the molecules i s as i n Table I V . 2 Order parameters o b t a i n e d from the e x p e r i m e n t a l d i p o l a r c o u p l i n g c o n s t a n t s . The b r a c k e t e d numbers are e r r o r s . Order parameters c a l c u l a t e d u s i n g the s i z e and shape program w i t h c o o r d i n a t e s i n Table I V . 2 as i n p u t . These v a l u e s have been f i t t e d by the l e a s t squares method to o b t a i n o p t i m a l agreement w i t h e x p e r i - mental v a l u e s . - 62 - IV.2 Furan and Thiophene The proton spectra of furan and thiophene obtained in: (i) 55 wt% 1132 in the temperature range 304-325 K (dial T) and (ii) the component liquid crystals: 1132 and EBBA at 301.4 K were similarly analyzed using LEQUOR and SHAPE. The geometries used were from Table IV.2 and the indirect couplings from Ref. 33 and 34. The experimental spectral parameters are listed in Tables IV.4 and IV.5 and the orientation parameters in Tables IV.6 and IV.7. In the tempera- ture study, i t was noted that the magnitude of a l l the order parameters decrease steadily with increase in temperature. - 63 - Table IV.4: Experimental di p o l a r c o u p l i n g s 3 (Hz), the chemical s h i f t differences (Hz), and the rms errors' 3 (Hz) obtained from LEQUOR f o r furan and thiophene dissolved i n the nematic l i q u i d c r y s t a l 55 wt% 1132 at various temperatures. Temperature (K) Parameter ( d i a l T) Furan c Thiophene' 306 D 1 2 D 1 3 D 14 D 2 3 v2'v\ rms -289.05 ( 6 ) d -108.43 (7) •154.69 (6) -511.23 (7) 372.68 (12) 0.20 -538.84 (3) - 97.03 (4) - 73.47 (6) -371.27 (6) 85.31 (14) 0.14 308 D 1 2 D 1 3 Dl4 D 23 rms •285.61 (15) -106.16 (16) -151.07 (15) -499.01 (18) 373.5 (3) 0.45 •528.23 (3) • 94.91 (3) • 71.77 (5) -362.66 (5) 85.43 (12) 0.12 310 D 1 2 D 1 3 D 14 D 23 v2'vl rms -281.87 (5) -103.87 (6) -147.34 (6) -486.76 (7) 374.79 (12) 0.17 •517.34 (2) • 92.77 (2) • 70.00 (4) •354.08 (4) 85.42 (10) 0.10 - 64 - 312 D 1 2 -277.88 (3) -505.86 (3) D 1 3 -101.53 (4) - 90.56 (3) D 1 4 -143.58 (4) - 68.24 (5) D 2 3 -474.39 (4) -344.91 (5) u2-v\ 376.00 (7) 85.63 (13) rms 0.19 0.12 314 D 1 2 -273.46 (4) -493.96 (3) D 1 3 - 99.11 (5) - 88.22 (4) D 1 4 -139.64 (5) - 66.42 (7) D 2 3 -461.20 (6) -335.75 (7) i / 2 - i / 1 377.35 (10) 85.68 (15) rms 0.12 0.15 320 D 1 2 -259.88 (12) -452.47 (5) D 1 3 - 91.82 (13) - 80.33 (6) D 1 4 -128.62 (13) - 60.29 (11) D 2 3 -425.54 (17) -304.61 (11) u1-u1 380.4 (3) 85.9 (3) rms 0.34 0.24 325 D 1 2 -243.48 (14) -413.8 (2) D 1 3 - 84.52 (16) - 73.4 (3) D 1 4 -117.17 (16) - 54.3 (5) D 2 3 -387.10 (2) -276.9 (5) - 65 - 384.0 (3) 86 (1) rms 0.47 1.10 The numbering of furan and thiophene i s as i n Table IV.2. Rms error of the f i t of the experimental to the calculated spectra by the program LEQUOR. The in d i r e c t couplings are as i n Table IV.1. Numbers i n brackets refer to errors. - 66 - Table IV.5 a: Experimental dipolar couplings (Hz), the chemical s h i f t differences (Hz), and the rms errors (Hz) obtained from LEQUOR f o r furan and thiophene dissolved In the nematic l i q u i d c r y s t a l s 1132 and EBBA at 301.4 K. L i q u i d C r y s t a l i Spectral Parameters Furan Thiophene 1132 EBBA D 1 2 -253, .42 ( 1 8 ) b -695 .95 (4) D 1 3 -181, .06 (19) -160 .76 (4) Dl4 -302, .39 (9) -143 .64 (6) D 23 -996, .93 (10) -723 .01 (6) v2-vi 332, .77 (2) 49 .46 (15) rms 0, .34 0, .16 D 1 2 -349, ,86 (3) -460. .82 (11) D 13 - 36. ,12 (4) - 29. ,52 (13) Dl4 - 2. ,93 (4) 10. ,50 (4) D 2 3 - 13. ,31 (4) 50. ,8 (4) u2-v1 416. ,79 (10) 143. ,1 (2) rms 0. 13 0. 48 I n d i r e c t couplings used are as i n Table I V . 1 . Numbers i n brackets denote errors. - 67 - Table IV.6 a: Experimental order parameters of furan and thiophene dissolved i n the l i q u i d c r y s t a l 55 wt% 1132 at various temperatures. Temperature (K) ( d i a l T) Order Parameter^ Furan Thiophene 304 'xx yy 'zz 0.0907 (1) 0.0457 (2) -0.1365 (1) 0.0586 (1) 0.0905 (5) -0.1490 (4) 306 'xx yy 'zz 0.0884 (1) 0.0452 (3) -0.1335 (2) 0.0572 (1) 0.0887 (3) -0.1459 (2) 308 'xx yy 'zz 0.0863 (1) 0.0448 (5) -0.1311 (4) 0.0559 (1) 0.0868 (3) -0.1427 (2) 310 'xx Jyy 'zz 0.0841 (1) 0.0443 (3) -0.1285 (2) 0.0545 (1) 0.0850 (3) -0.1395 (2) 312 'xx Jyy 'zz 0.0820 (1) 0.0437 (2) •0.1258 (1) 0.0531 (1) 0.0832 (3) •0.1363 (2) - 68 - 314 J x x yy ZZ 0.0798 (1) 0.0430 (2) •0.1227 (1) 0.0517 (1) 0.0809 (3) -0.1326 (2) 320 yy ZZ 0.0735 (1) 0.0418 (5) •0.1152 (4) 0.0469 (1) 0.0737 (5) -0.1206 (4) 325 -"xx yy 'ZZ 0.0669 (1) 0.0389 (7) •0.1055 (6) 0.0423 (4) 0.0690 (21) -0.1113 (17) The m o l e c u l a r a x i s system of f u r a n and thiophene i s as i n Table I V . 2 . D The numbers i n b r a c k e t s denote e r r o r s . - 69 - Table I V . 7 : E x p e r i m e n t a l o r d e r parameters of f u r a n and thiophene i n 1132 and EBBA at 301.4 K L i q u i d C r y s t a l Order Parameters a Furan Thiophene 1132 S x x 0.1727 (1) 0.1118 (1) Syy 0.0336 (3) 0.0871 (5) S z z -0.2063 (2) -0.1990 (4) EBBA S x x 0.0017 (1) -0.0082 (3) Syy 0.0548 (4) 0.0819 (13) S z z -0.0565 (3) -0.0737 (10) The numbers i n b r a c k e t s denote e r r o r s . - 70 - CHAPTER V DISCUSSION - 71 - V . DISCUSSION The component, S-pq> ° f t * i e o rder tensor o f a molecule i s g i v e n by the e x p r e s s i o n : S p q - d / 2 ) <3 c o s 0 p c o s f ? q - S p q > [8] p , q = x , y , z E q u a t i o n [8] d e f i n e s the range of the order parameter t o be -0 .5 <S<1 f o r p — q . For example i f S z z - 1, the molecule f i x e d z - a x i s i s on average o r i e n t e d p a r a l l e l to the a p p l i e d magnetic f i e l d ; and i f S z z = - 0 . 5 , p e r p e n d i c u l a r to i t . For S z z •= 0, there are two p o s s i b l e c o n t r i b u t i n g f a c t o r s : ( i ) the average o r i e n t a t i o n o f the m o l e c u l a r z - a x i s i s a t 5 4 . 7 4 ° or ( i i ) a l l o r i e n t a t i o n s o f the z - a x i s are e q u a l l y p r o b a b l e . The o r i e n t a t i o n o f a molecule i n a l i q u i d c r y s t a l l i n e system i s dependent on the type o f i n t e r a c t i o n s between the s o l v e n t and s o l u t e m o l e c u l e s . I n the recent s tudy by van der Es t e t a l . 2 2 the s i z e and shape, and the e fg -quadrupole moment i n t e r a c t i o n s were found to p l a y impor tant r o l e s i n the o r i e n t a t i o n o f a s e r i e s of s o l u t e s . The s i z e and shape mechanism i s f u r t h e r i n v e s t i g a t e d i n t h i s work. The l i q u i d c r y s t a l s o l v e n t used f o r the s tudy of t h i s mechanism i s the 55 wt% 1132 m i x t u r e . I n t h i s l i q u i d c r y s t a l , D 2 exper iences a zero e l e c t r i c f i e l d g r a d i e n t , and i t i s assumed t h a t o ther s o l u t e s exper ience - 72 - the same zero e f g . A l l the samples used were made by d i s s o l v i n g the minimum amount o f s o l u t e (1 mole percent ) i n the l i q u i d c r y s t a l . T h i s c o n c e n t r a t i o n approximates i n f i n i t e d i l u t i o n where there i s l e a s t d i s r u p t i o n i n the o r d e r i n g of the l i q u i d c r y s t a l m o l e c u l e s . V . l O r i e n t a t i o n of S o l u t e s i n 55 wt% 1132 - Q u a l i t a t i v e Survey From the r e s u l t s o f the v a r i e t y of s o l u t e s d i s s o l v e d i n 55 wt% 1132 (Table I V . 3 ) , i t i s noted t h a t g e n e r a l l y the axes o f l o n g e s t m o l e c u l a r dimensions have the most p o s i t i v e S - v a l u e s . T h i s agrees w i t h one 's i n t u i t i o n t h a t s o l u t e s s h o u l d tend to o r i e n t w i t h t h e i r l o n g e s t molecu- l a r d imens ion a l o n g the d i r e c t o r of the l i q u i d c r y s t a l , where l e a s t d i s r u p t i o n o f the l i q u i d c r y s t a l molecules i s caused. T h i s i s c l e a r l y seen i n the molecule TTF. On average, i t o r i e n t s such t h a t the g r e a t e s t l e n g t h o f the molecule i s a l o n g the d i r e c t o r a x i s . An examinat ion of the monosubst i tu ted benzenes showed t h a t the s i z e o f the s o l u t e s i s important i n d e t e r m i n i n g t h e i r o r i e n t a t i o n . The order parameters o f f l u o r o b e n z e n e : S x x = 0.0507, Syy •= 0.1399 and S z z = -0.1906 i n d i c a t e t h a t the C 2 a x i s and the plane of the r i n g o f t h i s s o l u t e i s a l i g n e d p r e f e r e n t i a l l y a l o n g the nematic a x i s . T h i s i s even more pronounced i n the case o f chlorobenzene and iodobenzene. In t h i s s e r i e s o f three m o l e c u l e s , as the s u b s t i t u e n t ha logen i n c r e a s e s i n s i z e , S x x p r o g r e s s i v e l y decreases and Syy i n c r e a s e s . T h i s i n d i c a t e s t h a t as the s u b s t i t u e n t ha logen atom becomes l a r g e r , the C-X d i r e c t i o n (X = halogen) i . e . the y a x i s , becomes more o r i e n t e d a l o n g the d i r e c t o r a x i s . - 73 - On comparing r e s u l t s f o r 1 , 2 - d i c h l o r o b e n z e n e and 1 ,2-dicyanobenzene i t i s noted t h a t the symmetry a x i s of the c y a n o - s u b s t i t u t e d r i n g i s more a l i g n e d a l o n g the nematic a x i s than t h a t of d i c h l o r o b e n z e n e . T h i s i s expected because the cyano-group i s b i g g e r and l o n g e r a l o n g the y - d i r e c - t i o n o f the m o l e c u l e - f i x e d a x i s than the c h l o r i n e atoms. T h i s t r e n d i s a l s o observed i n the 1 , 4 - d i s u b s t i t u t e d benzenes. The more b u l k y dibromobenzene i s o r i e n t e d w i t h i t s symmetry a x i s p r e f e r e n t i a l l y a long the nematic a x i s as compared to 1 , 4 - d i c h l o r o b e n z e n e . I t i s a l s o i n t e r - e s t i n g to note the r e s u l t s o b t a i n e d f o r the f o l l o w i n g s e r i e s of com- pounds: c h l o r o - , 1 , 2 - d i c h l o r o - , 1 , 3 - d i c h l o r o - and 1 , 4 - d i c h l o r o - b e n z e n e . The o r i e n t a t i o n of the r i n g changes w i t h the p o s i t i o n o f s u b s t i t u t i o n of c h l o r i n e atoms. I n each case , the s o l u t e i s a l i g n e d such t h a t the l o n g e s t m o l e c u l a r dimension i s a long the d i r e c t o r a x i s . For molecules which have s i m i l a r l e n g t h and b r e a d t h d imens ions , i t i s not obvious as to which o r i e n t a t i o n i s f a v o r e d . T h i s i s seen i n the case o f acetone. The order parameters are a l l q u i t e s m a l l i n d i c a t i n g t h a t the o r i e n t a t i o n i s almost e q u a l l y probable i n a l l d i r e c t i o n s . T h i s b r i e f survey o f the r e s u l t s o b t a i n e d f o r C 2 v molecules shows t h a t g e n e r a l l y t h e i r m o l e c u l a r dimensions are important i n d e t e r m i n i n g t h e i r o r i e n t a t i o n . Thus i n t r y i n g to unders tand the mechanism r e s p o n s i b l e , the s i z e and shape model proposed by van der E s t " i s used to determine o r i e n t a t i o n a l o r d e r i n these m o l e c u l e s . - 74 - V . 2 The S i z e and Shape Model V . 2 . 1 P r e d i c t i o n of O r i e n t a t i o n of S o l u t e s The s i z e and shape model takes o n l y the s h o r t range r e p u l s i v e f o r c e s a c t i n g between s o l u t e and l i q u i d c r y s t a l molecules to be respon- s i b l e f o r o r i e n t a t i o n . The mean f i e l d approach i s used where the l i q u i d c r y s t a l molecules are r e p l a c e d by an a n i s o t r o p i c continuum; they are model led as an e l a s t i c tube . The s o l u t e m o l e c u l e s , assumed r i g i d , f i t i n t o and s t r e t c h t h i s tube . The mean p o t e n t i a l energy o f the system a r i s e s from t h i s s t r e t c h i n g o f the e l a s t i c w a l l s o f the tube by the s o l u t e m o l e c u l e s . The two i n t e r a c t i n g s u r f a c e s i . e . t h a t o f the s o l u t e s and the tube , are assumed to be h a r d s u r f a c e s . These s h o r t range i n t e r a c t i o n s are dependent on the s i z e and shape o f the s o l u t e s (see T h e o r y ) . T h i s model ignores s p e c i f i c i n t e r a c t i o n s , f o r example H-bond- i n g , and w i l l break down i n the presence of such i n t e r a c t i o n s . The model i s used to p r e d i c t the o r i e n t a t i o n a l parameters o f a l l the s o l u t e s i n t h i s 55 wt% 1132 system (see S e c t i o n I I I . 2 ) . The c a l c u - l a t e d parameters : S x x , Syy and S 2 Z are p l o t t e d a g a i n s t the exper imenta l r e s u l t s i n F i g s . V . l , V . 2 , and V . 3 r e s p e c t i v e l y . The van der Waals r a d i i were taken from R e f . 57. The a d j u s t a b l e parameter , the f o r c e c o n s t a n t , k , was o b t a i n e d by a l e a s t squares f i t procedure u s i n g two independent parameters S x x - S y y and S 2 Z , o f a l l the s o l u t e s to o b t a i n o p t i m a l agreement between t h e o r e t i c a l and e x p e r i m e n t a l r e s u l t s . The v a l u e o f k was found to be 5.2 dyne/cm. As can be seen from the p l o t s , the c o r r e l a t i o n i s good. I n F i g s . V . l and V . 2 , i t i s noted t h a t most of o _ J < o m 0 . 3 7 8 0 . 2 5 2 0 . 1 2 6 0 . 0 0 0 • 0 . 1 2 6 — 1 O — 13 / 12 — o 6 — 4 / o ° 5 3 y4>  11. 10 S 2 — / 14 15 I I o 9 I I I 1 1 • 0 . 1 2 6 0 . 0 0 0 0 . 1 2 6 S ( E X P T L ) 0 . 2 5 2 0 . 3 7 8 Fig. V.l Size and shape model: calculated versus experimental order parameters S x x of solutes in 55 wt% 1132. The labelling of the points refers to molecules indicated in Table IV.2 Fig. V.2 Size and shape model: calculated versus experimental order parameters Syy of solutes in 55 vt% 1132. The labelling of points refers to molecules lis t e d in Table IV.2 - 77 - the points l i e below the u n i t slope l i n e i . e . the predicted values for S x x and Syy are generally smaller than experimental values. Since the order matrix i s t r a c e l e s s , the S z z c a l c u l a t e d are then larger than experimental r e s u l t s (Fig. V.3). The observed deviations can be explained by factors discussed i n the next section. F i g . V . 4 shows a p l o t of the asymmetry parameter r), c a l c u l a t e d versus experimental. This parameter i s defined as: Jxx ' z z [18] The two independent parameters S x x-Syy and S z z describe the o r i e n t a t i o n of the same solute, and are dependent on the environment i n the same way. r) i s independent of the force constant (for small k) i n d i c a t i n g that t h i s r a t i o i s to a good approximation independent of the environ- ment. This allows one to determine how well the r e l a t i o n s h i p between order parameters of i n d i v i d u a l solutes i s predicted. Consequently, i t i s a b e t t e r i n d i c a t i o n of how good the c o r r e l a t i o n i s between c a l c u l a t e d and experimental r e s u l t s for each solute. As can be seen from the p l o t of rj i n F i g . V.4, although there are some deviations, the c o r r e l a t i o n i s remarkably good i n d i c a t i n g that the o r i e n t a t i o n i s well predicted for each solute. - 0 . 0 2 0 •310 - 0 . 2 5 2 - 0 . 1 9 4 - 0 . 1 3 6 - 0 . 0 7 8 - 0 . 0 2 0 S ( E X P T L ) Fig. V.3 o _) < 2.12 — 15 / 14 / o / o / 1.06 11 / 1 0 0.00 5 >X ° o / 4 6 / 3 - 1 . 0 6 >^ c? 13 >X 12 - 2 . 12 °1 I I I I I I l I I - 2 . 1 2 - 1 . 06 0 .00 n(EXPTL) 1.06 2.12 Fig. V .4 Size and shape model: calculated versus experimental **xx " Syy parameters tj - of solutes ln 55 wt% 1132. The numbering of points are the molecules l i s t e d in Table IV.2 V O - 80 - V.2.2 Factors Causing Deviations i n P r e d i c t e d O r i e n t a t i o n s The s l i g h t deviations from the experimental parameters of the solutes as observed i n Figs. V . l , V.2, V.3, and V.4 can be explained i n terms of the assumptions made i n studying t h i s system. The s i z e and shape p i c t u r e that was used i s not an exact and accurate d e s c r i p t i o n of the l i q u i d c r y s t a l l i n e system. As mentioned, the mean f i e l d approach i s taken where the i n d i v i d u a l l i q u i d c r y s t a l molecules are replaced by a continuum. A l l the solutes are assumed to experience a mean environ- ment. This i s not so i n the actual system where the l i q u i d c r y s t a l molecules are f l e x i b l e and e x i s t i n many d i f f e r e n t conformations. Therefore an exact d e s c r i p t i o n of the system would involve a l l the conformations of the l i q u i d c r y s t a l molecules. Since these molecules are replaced by an average environment i n the size and shape model, the predicted order parameters w i l l d i f f e r from the experimental values. However, as the deviation i s not of a large magnitude, the mean f i e l d d e s c r i p t i o n of the system i s adequate. In f a c t the c o r r e l a t i o n i s s u r p r i s i n g l y much better than expected for t h i s s i m p l i s t i c p i c t u r e . In the model used, i t was also assumed that a l l the solute mole- cules experience the same mean environment. A l l the molecules are assumed to experience no f i e l d gradient based on the f a c t that D 2 experiences a zero efg. The EBBA molecules are long and co n s i s t of two benzene rings and an a l k y l chain. I t i s l i k e l y that the e l e c t r i c f i e l d gradient near the rings w i l l d i f f e r from that which i s close to the a l k y l chains. D 2, being a small molecule can occupy c e r t a i n ' s i t e s ' where i t sees a zero efg. Other large solute molecules may not occupy - 81 - the same ' s i t e s ' . This has been shown by Buckingham et a l . 5 8 i n the case of tetramethylsilane (TMS), C H 4 , C F 4 and SFg. These molecules occupy d i f f e r e n t s i t e s as indicated by differences i n l o c a l solvent anisotropy e f f e c t s (on the chemical s h i e l d i n g ) . In t h i s study, the lar g e r solute molecules may not occupy the same ' s i t e s ' . Consequently they w i l l experience d i f f e r e n t environments e.g. the presence of some efg due to t h e i r proximity to d i f f e r e n t parts of the l i q u i d c r y s t a l molecules. Thus some efg-molecular quadrupole moment in t e r a c t i o n s may be present and t h i s would contribute towards the o r i e n t a t i o n of the molecules. Consequently deviations from the predicted parameters w i l l then be seen. D i f f e r e n t mean environments may also a r i s e from s l i g h t concentra- t i o n and temperature v a r i a t i o n s i n d i f f e r e n t samples. The order para- meter S i s to a good approximation proportional to the i n t e r a c t i o n energy U, which i s i n turn dependent on the product of two factors as given below: KU GB C S [19] k BT where K and C are constants G i s some property of the l i q u i d c r y s t a l B i s some property of the solutes This equation applies only when « 1. knT - 82 - G i s a f u n c t i o n of the order parameter o f the l i q u i d c r y s t a l m o l e c u l e s . A l t e r i n g the c o n c e n t r a t i o n o f the s o l u t e molecules w i l l a f f e c t the o r d e r i n g o f the l i q u i d c r y s t a l s . The v a l u e o f G i s then changed and t h i s w i l l , i n t u r n , v a r y the order parameter S o f the s o l u t e s . T h i s i s a l s o i n t u i t i v e l y obvious i n t h a t i n c r e a s i n g the number of s o l u t e mole- c u l e s w i l l cause a d i s r u p t i o n i n the o r d e r i n g o f the l i q u i d c r y s t a l molecules which then a l l o w s more o r i e n t a t i o n a l freedom i n the s o l u t e s . I n the model , S was c a l c u l a t e d assuming i n f i n i t e d i l u t i o n of the s o l u t e s where there i s no d i s r u p t i o n i n the p r o p e r t i e s of the l i q u i d c r y s t a l s . The o t h e r f a c t o r a f f e c t i n g S i s the temperature o f the system. The h i g h e r the temperature the lower the order parameter . The presence of these two f a c t o r s thus a f f e c t s the v a l u e of S o f the d i f f e r e n t s o l u t e s s t u d i e d . Another p o s s i b l e f a c t o r i s t h a t the model used c o n s i d e r e d o n l y s h o r t range h a r d body i n t e r a c t i o n s to be r e s p o n s i b l e f o r o r i e n t a t i o n i n the m o l e c u l e s . T h i s does n o t , however, mean t h a t there are no o ther types o f i n t e r a c t i o n s p r e s e n t . Short range a t t r a c t i v e f o r c e s between molecules were i g n o r e d and so were l o n g range i n t e r a c t i o n s . A l l these i f p r e s e n t c o u l d cause some d e v i a t i o n s between e x p e r i m e n t a l and t h e o r e t i c a l r e s u l t s . T h e r e f o r e , by c o n s i d e r i n g some of the assumptions o f the model , the s m a l l d e v i a t i o n s i n the c a l c u l a t e d parameters can be accounted f o r . I n g e n e r a l , i t has been shown t h a t the o r i e n t a t i o n o f the s e r i e s of C 2 v molecules i n 55 wt% 1132 can be p r e d i c t e d w e l l w i t h the s i z e and shape model . T h i s p i c t u r e i s s u c c e s s f u l i n m o d e l l i n g the s h o r t range hard body i n t e r a c t i o n , and thus the mean f i e l d approach, a l t h o u g h s i m p l e , i s - 83 - an adequate description. The results of this study give strong evidence that the size and shape of solutes is important in determining their orientation. Although other mechanisms related to the dimensions of the solutes cannot be completely ruled out, i t can be concluded that short range repulsive interactions must play a very important role. V.2.3 Effects of Temperature and Concentration Variations An attempt was made to determine i f the correlation between experi- mental and predicted parameters could be improved by removing concentra- tion and temperature variations among samples. In this study the liquid crystal EBBA was deuterated at two ring positions. (A set of results were also obtained for the series of solutes in a mixture of 55 wt% 1132 where the EBBA molecules were not deuterated. The results are presented in the Appendix). The deuteron spectrum of this compound is as shown in Fig. IV.3. The two C-D directions of the EBBA in the 55 wt% mixture give two doublets with quadrupolar splittings of 19 and 16 kHz in the spectrum. The splittings provide a measure of the ordering of the liquid crystal molecules. Therefore, any differences in the liquid crystal environment - 84 - w i l l a f f e c t the s p l i t t i n g s . The more disorder there i s , the smaller w i l l be the s p l i t t i n g s . Thus, any e f f e c t s due to varying concentration of the solutes and temperature which disrupt the l i q u i d c r y s t a l mole- cules should show up i n the s p l i t t i n g s i n the deuteron spectrum. For each sample, a deuteron spectrum was c o l l e c t e d and the quadrupolar s p l i t t i n g s measured. The experimental order parameters were scaled as follows: s s c a l e d ~ ~ X S e x p t l [ 2 0 ] A "solute where Ai/pj^ the quadrupolar s p l i t t i n g s of EBBA i n the sample of D 2 i n 55 wt% 1132 mixture Absolute i s the quadrupolar s p l i t t i n g s of EBBA i n the i n d i v i d u a l solute sample. The standard chosen f o r s c a l i n g was the s p l i t t i n g from the D 2 sample because t h i s was used to determine the efg i n the mixture. The two sets of experimental order parameters, scaled and unsealed, are compared with the t h e o r e t i c a l values i n the following two f i g u r e s . F i g . V.5 i s the p l o t of a l l the S (unsealed) versus c a l c u l a t e d values. The k value obtained from the l e a s t squares f i t of these r e s u l t s i s 5.2 dyne/cm, and the c o r r e l a t i o n c o e f f i c i e n t i s 0.980. The p l o t of S (scaled) versus t h e o r e t i c a l values i s as shown i n F i g . V.6. The k value here i s 5.3 dyne/cm, and the c o r r e l a t i o n c o e f f i c i e n t i s 0.979. Unsealed order parameters and k values were reported i n section IV and throughout the 0 . 3 0 8 - 0 . 1 5 4 - o _ i < o </f 0 . 0 0 0 • 0 . 1 5 4 0 . 3 0 8 • 0 . 3 0 8 - 0 . 1 5 4 0 . 0 0 0 0 . 1 5 4 0 . 3 0 8 S ( E X P T L ) 00 Fig. V.5 Theoretical versus unsealed experimental order parameters: sxx> syy a n d s z z o f solutes In 55 vt% 1132. The k value from the least squares f i t of this data i s 5.2 dyne/cm. Correla- tion coefficient is 0.980. 0 . 3 0 8 0 . 1 5 4 - _ j < o w 0 . 0 0 0 0 . 1 5 4 - 0 . 3 0 8 - 0 . 3 0 8 - 0 . 1 5 4 0 . 0 0 0 0 . 1 5 4 0 . 3 0 8 S ( E X P T L ) OO IT. Fig. V .6 Theoretical versus scaled experimental order parameters: S x x, Syy, S Z 2 of solutes in 55 wt% 1132. The value of k from this data is 5.3 dyne/cm. Correlation coefficient is 0.979. - 87 - t h e s i s . A comparison of Figs. V.5 and V.6 shows that the s c a l i n g did not a l t e r the order parameter by any s i g n i f i c a n t magnitude. The maximum co r r e c t i o n i n the experimental order parameters occurred f o r the solute 2,6-difluoropyridine and was -5%. For the r e s t of the solutes, the percent change v a r i e d from 0 to 5. The c o r r e l a t i o n c o e f f i c i e n t s indicate that the scaled r e s u l t s gave a s l i g h t l y worse f i t than the unsealed. The s c a l i n g of order parameters d i d not improve c o r r e l a t i o n between theory and experiment. Instead, small random scatte r i n the experimental parameters was introduced by the s c a l i n g . The small corrections, which may have r e s u l t e d p a r t l y from errors i n determining the quadrupole s p l i t t i n g s Ai>, cannot account for the l a r g e r deviations of theory from experiment. These r e s u l t s then in d i c a t e that v a r i a t i o n s among samples due to concentration and tempera- ture were e i t h e r n e g l i g i b l e or d i d not s i g n i f i c a n t l y a f f e c t the s p l i t t i n g s i n the spectrum. V.3 Furan and Thiophene V.3.1 Component L i q u i d C r y s t a l Study The o r i e n t a t i o n of furan and thiophene i n each of the l i q u i d c r y s t a l s 1132 and EBBA was examined. In these l i q u i d c r y s t a l s , a large e l e c t r i c f i e l d gradient i s known to be present and as such the e f f e c t of the efg-quadrupole moment mechanism i s expected to be large. An attempt was made to p r e d i c t the order parameters for furan and thiophene due to - 88 - the efg mechanism. The following r e l a t i o n s h i p was assumed to be true, i . e . the t o t a l order parameter can be written as a sum of parameters: s t o t = s e f g + s s s t 2 1 ] where S t o t i s the order parameter f o r the solutes i n the l i q u i d c r y s t a l s S e f g i s the order parameter due to the efg-quadrupole moment mechanism S s s i s the order parameter due to the size and shape mechanism, i . e . the order parameter i n 55 wt% 1132 (Table IV.3). Calculations of the order parameters S t o t were done by including both mechanisms, s i z e and shape and efg-quadrupole moment, i n the s i z e and shape program. The value of F^z *-n 11-32 and EBBA were obtained from a previous experiment on D2.^' 2^ The value of k was a r b i t r a r i l y chosen to be the s ame as the unsealed k value i n the 55 wt% 1132. Quadrupole moments f o r furan and thiophene were obtained from Ref. 59. Th e o r e t i c a l values of $e£g w e r e then obtained by subtracting c a l c u l a t e d S s s (Table IV. 3) from c a l c u l a t e d S t o t . Experimental values of S e f g were obtained from the differ e n c e of S t o t (exptl) and S s s ( e x p t l ) . Results f o r S e f g (calculated versus experimental) i s given i n Figs. V. 7 and V.8 and Table V . l . The c o r r e l a t i o n between c a l c u l a t e d and experimental values i s quite good considering that there are no adjust- able parameters involved, and that large errors were associated with molecular quadrupole moments used. Therefore the o r i e n t a t i o n of furan and thiophene due to the efg-quadrupole moment mechanism can be - 0 . 1 3 2 - 0 . 0 6 6 0 . 0 0 0 0 . 0 6 6 0 . 1 3 2 S e f g ( E X P T ) Fig. V.7 Electric f i e l d gradient-quadrupole moment mechanism calcu- lated versus experimental order parameters: S e f R of furan and thiophene in 1132. T - 301.4 K.F Z Z (1132) - 6.067 x 10 1 1 esu. O are the order parameters of furan. + are the order parameters of thiophene - 0 . 1 4 4 - 0 . 0 7 2 0 . 0 0 0 0 . 0 7 2 0 . 1 4 4 S e f g ( E X P T ) Fig. V.8 Electric f i e l d gradient-quadrupole moment mechanism calcu- lated versus experimental order parameters: S ef_ of furan and thiophene In EBBA. T - 301.4 K.F Z Z (EBBA) - -6.420 x 10 1 1 esu. o are the order parameters of furan. + are the order parameters of thiophene - 91 - Table V . l : E l e c t r i c f i e l d gradient-quadrupole moment mechanism: c a l c u l a t e d 3 and experimental order parameters of furan and thiophene i n 1132 and EBBA. L i q u i d C r y s t a l Order Parameters" ( S e f g ) Furan Thiophene Exper imenta l C a l c u l a t e d E x p e r i m e n t a l C a l c u l a t e d 1132 S x x 0.0820 (2) -0.0122 (5) S z z -0.0698 (3) 0.1352 -0.0318 -0.1034 0.0532 (2) -0.0034 (10) -0.0500 (8) 0.1342 -0.0069 -0.1273 EBBA 5 xx -0.0890 (2) Syy 0.0090 (6) 3 z z 0.0800 (4) -0.1198 0.0012 0.1186 -0.0668 (4) -0.0086 (18) 0.0753 (14) -0.1280 -0.0367 0.1647 Quadrupole moment o f f u r a n and thiophene were o b t a i n e d from Ref . 59. k •= 5.2 dyne/cm, assumed to be the same as i n 55 wt% 1132. F z z (1132) - 6.067 x 1 0 1 1 esu F z z (EBBA) - -5.748 x 1 0 1 1 esu E q u a t i o n [21] : S e f g = S t o t 'ss ' t o t order parameter i n component l i q u i d c r y s t a l s S e f g = order parameter due to e fg -quadrupole moment mechani sm. 'ss o r d e r parameter due to s i z e and shape mechanism (va lue from 55 wt% 1132. - 92 - p r e d i c t e d f a i r l y w e l l . The o r i e n t a t i o n o f these two molecules i n these l i q u i d c r y s t a l s can be e x p l a i n e d u s i n g the two mechanisms: s i z e and shape, and e fg -quadrupole moment. T h i s p i e c e o f evidence t i e s i n w i t h van der E s t ' s r e s u l t s 2 2 which show t h a t the o r i e n t a t i o n o f molecules can be e x p l a i n e d u s i n g these mechanisms. V . 3 .2 Temperature Study The o r i e n t a t i o n o f f u r a n and thiophene i n 55 wt% 1132 was s t u d i e d as a f u n c t i o n o f temperature . The temperature range chosen: 304-325 K ( d i a l T ) , i s w i t h i n the nematic phase of the l i q u i d c r y s t a l l i n e m i x t u r e . The magnitude o f the order parameters f o r bo th s o l u t e s were found to decrease s t e a d i l y w i t h i n c r e a s e of temperature (Table I V . 6 , F i g s . V . 9 to V . 1 4 ) . T h i s i s expected because a t h i g h e r temperatures , the l i q u i d c r y s t a l molecules possess more thermal energy, thus e x h i b i t i n g more m o t i o n . As a r e s u l t , the o r d e r i n g o f these molecules i s lowered which i n t u r n reduces the o r i e n t a t i o n a l o r d e r i n the s o l u t e s . The temperature dependence of S was c a l c u l a t e d u s i n g the s i z e and shape program. The e fg -quadrupole moment mechanism was i n c l u d e d i n a d d i t i o n to the s i z e and shape i n t e r a c t i o n . The e f g a t each temperature were determined from D 2 exper iments . Furan and thiophene were assumed to exper ience the same e f g as D 2 a t these temperatures . Quadrupole moments were o b t a i n e d from Ref . 59. The v a l u e s o f k f o r d i f f e r e n t temperatures were es t imated by s c a l i n g w i t h the quadrupolar s p l i t t i n g s - 93 - o f EBBA. Here k i s assumed to v a r y p r o p o r t i o n a l l y w i t h the o r i e n t a t i o n o f the C-D bond d i r e c t i o n of EBBA. k T . x k 3 0 1 . 4 [22] A l / 3 0 1 . 4 where k>p i s the f o r c e constant a t temperature T. ^301 4 t n e f ° r c e cons tant o b t a i n e d from u n s e a l e d r e s u l t s a t temperature 301.4 K. hvj i s the quadrupolar s p l i t t i n g o f EBBA a t temperature T. A " 3 0 1 . 4 i s t h e s p l i t t i n g a t 301.4 K. The c a l c u l a t e d r e s u l t s are p l o t t e d i n F i g s . V . 9 to V . 1 4 . A t a f i r s t g l a n c e , the magnitude of the p r e d i c t e d order parameters appears to be q u i t e d i f f e r e n t from t h a t of e x p e r i m e n t a l r e s u l t s . T h i s d i f f e r e n c e i s , however, o f the same magnitude as t h a t i n the whole s e r i e s o f s o l u t e s . The probable f a c t o r s c a u s i n g these d e v i a t i o n s have been d i s c u s s e d i n S e c t i o n V . 2 . 2 . On the o ther hand, the temperature dependence o f the order parameters i s g e n e r a l l y w e l l - p r e d i c t e d . C a l c u - l a t e d and e x p e r i m e n t a l v a l u e s of S x x and Syy decrease w i t h temperature . Both t h e o r e t i c a l and observed S z z v a l u e s i n c r e a s e w i t h i n c r e a s e of temperature . The c o r r e l a t i o n between theory and experiment of the temperature dependence o f S i s q u i t e good i n d i c a t i n g t h a t the assumptions made r e g a r d i n g the temperature dependence of e f g and k were r e a s o n a b l e . Furan and thiophene were assumed to exper ience the same v a r i a t i o n i n e f g - 94 - w i t h temperature as D 2 m o l e c u l e s . I n the contex t o f the model , the exact dependence o f k on Au^ and temperature i s not known. As temperature i n c r e a s e s , o r d e r i n g of l i q u i d c r y s t a l molecules decreases , thus l e s s f o r c e i s needed to push the w a l l s o f the e l a s t i c tube a p a r t . The f o r c e cons tant s h o u l d then decrease . I t seemed reasonable to assume t h a t k s h o u l d v a r y p r o p o r t i o n a l l y w i t h Au^ as temperature i s changed. The r e s u l t s show t h i s to be v a l i d . The change i n o r i e n t a t i o n a l b e h a v i o r of f u r a n and thiophene i n the 55 wt% 1132 can be e x p l a i n e d by the two mechanisms: e f g - q u a d r u p o l e moment, and s i z e and shape. 0 . 1 5 2 - 0 . 1 1 4 - 0 . 0 7 6 - 0 . 0 3 8 - 0 . 0 0 0 - 3 0 0 3 0 6 3 1 2 3 1 8 3 2 4 T E M P E R A T U R E ( K ) 3 3 0 Fig. V.9 Temperature dependence of the order parameters S x x (calculated and experimental) of furan ln 55 wt% 1132 © refers to the experimental results • refers to the calculated results 0 . 1 1 4 0 . 0 7 6 00 0 . 0 3 8 o O O O O O 0 . 0 0 0 - 0 . 0 3 8 VO 3 0 0 3 0 6 3 1 2 3 1 8 T E M P E R A T U R E ( K ) 3 2 4 3 3 0 Fig. V.10 Temperature dependence of the order parameters S_y calculated and experimental) of furan in 55 wt% 1132 © refers to the experimental results • refers to the calculated results 0 . 0 0 5 0 . 0 4 3 0 . 0 8 1 0 . 1 1 9 0 . 1 5 7 0 . 1 9 5 3 0 0 3 0 6 3 1 2 3 1 8 3 2 4 T E M P E R A T U R E ( K ) 3 3 0 Fig. V . l l Temperature dependence of the order parameters: S 2 Z- calculated (•) and experimental (a), of furan in 55 wt% 1132 0 . 1 2 8 0 . 0 9 6 0 . 0 6 4 0 . 0 3 2 - 0 . 0 0 0 3 0 0 3 0 6 3 1 2 3 1 8 3 2 4 T E M P E R A T U R E ( K ) 3 3 0 Fig. V.12 Temperature dependence of the order parameters: S x x- calculated (•) and experimental (©), of thiophene in 55 wt% 1132 0 . 1 2 8 0 . 0 9 6 - 0 . 0 6 4 0 . 0 3 2 - 0 . 0 0 0 - 3 0 0 3 0 6 3 1 2 3 1 8 T E M P E R A T U R E ( K ) 3 2 4 3 3 0 Fig. V.13 Temperature dependence of the order parameters: S~- calculated (•) and experimental (©), of thiophene In 55 wt% 1132 0 . 0 3 5 0 . 0 6 7 0 . 0 9 9 - 0 . 1 3 1 0 . 1 6 3 0 . 1 9 5 3 0 0 3 0 6 3 1 2 3 1 8 3 2 4 T E M P E R A T U R E ( K ) 3 3 0 Fig. V.14 Temperature dependence of the order parameters: Szz- calculated (•) and experimental (©), of thiophene in 55 wt% 1132 - 101 - CHAPTER VI CONCLUSION - 102 - V I . CONCLUSION The r e s u l t s of a s e r i e s of C 2 v molecules i n 55 wt% 1132 i n d i c a t e t h a t i n t h i s l i q u i d c r y s t a l , o r i e n t a t i o n parameters o f s o l u t e s depend on t h e i r d i m e n s i o n s . The model based on s h o r t range h a r d body i n t e r a c t i o n s (dependent on the s i z e and shape of s o l u t e s ) i s s u c c e s s f u l i n d e s c r i b i n g the o r i e n t a t i o n a l b e h a v i o r of s o l u t e s . Order parameters c a l c u l a t e d are i n good agreement w i t h experiment d e s p i t e the v a r i o u s assumptions a s s o c i a t e d w i t h the model . These r e s u l t s support the c o n c l u s i o n t h a t o r i e n t a t i o n o f s o l u t e s i n 55 wt% 1132 i s dominated by s h o r t range h a r d body i n t e r a c t i o n s . The temperature dependence o f o r d e r i n g i n 55 wt% 1132, and o r i e n t a t i o n i n 1132 and EBBA, were w e l l p r e d i c t e d w i t h the i n c l u s i o n o f the e l e c t r i c f i e l d g r a d i e n t - q u a d r u p o l a r moment mechanism i n a d d i t i o n to s h o r t range h a r d body i n t e r a c t i o n s . - 1 03 - CHAPTER VII BIBLIOGRAPHY - 104 - VII. BIBLIOGRAPHY 1. J .W. Emsley, N u c l e a r Magnet ic Resonance o f l i q u i d C r y s t a l s , D. R e i d e l P u b l i s h i n g Company (1985). 2. G.R. L u c k h u r s t and G.W. Gray, M o l e c u l a r P h y s i c s o f L i q u i d C r y s - t a l s , Academic Press (1979). 3 . E . E . B u r n e l l and C . A . de Lange, Phys. Rev. A25, 2339 (1982). 4 . F . R e i n i t z e r , Monatsh, 9, 421 (1888). 5. 0 . Lehmann. " F l u s s i g e K r i s t a l l e , sowie P l a s t i z i t a t von K r i s t a l l e n im A l l g e m e i n e n , molekulare Umlagerungen und Aggregatzustand sanderungen" Engelmann, L i e p z i g , (1904). 6. G .R . L u c k h u r s t , Q u a r t . Rev. 22, 179 (1968). 7. A . Saupe and G. E n g l e r t , Phys . Rev. L e t t . 11, 462 (1963). 8. G. E n g l e r t and A . Saupe, Z . N a t u r f o r s c h . 19a, 172 (1964). 9. P . D i e h l , C . L . K h e t r a p a l , NMR B a s i c P r i n c i p l e s and Progress 1, 1 (1969) . 10. A . Saupe, M o l . C r y s t . 1, 231 (1971). 11. J . C . Rober t son , C T . Y i m , and D . F . R . G i l s o n , Can. J . Chem. 49, 2345 (1971). 12. E . T . S a m u l s k i , F e r r o e l e c t r i c s 31, 83 (1980). 13. J . M . Anderson , J . Magn. Reson. 4, 231 (1971). 14. J . G . S n i j d e r s , C . A . de Lange, and E . E . B u r n e l l , I s r a e l J . Chem. 23, 269 (1983) . 15. E . E . B u r n e l l and C . A . de Lange, J . Chem. Phys . 76, 3474 (1982). 16. J . G . S n i j d e r s , C . A . Lange, and E . E . B u r n e l l , J . Chem. Phys . 77, 5386 (1982). 17. J . G . S n i j d e r s , C . A . Lange, and E . E . B u r n e l l , J . Chem. Phys . 79, 2964 (1983). 18. A . J . van der E s t , P . B . B a r k e r , E . E . B u r n e l l , C . A . de Lange, and J . G . S n i j d e r s , M o l . Phys . 56, 161 (1985). 19. G . N . Pa tey , E . E . B u r n e l l , J . G . S n i j d e r s , and C . A . de Lange, Chem. Phys . L e t t . 99, 271 (1983). - 105 - 20. P . B . B a r k e r , A . J . van der E s t , E . E . B u r n e l l , C A . de Lange, and J . G . S n i j d e r s , Chem. Phys. L e t t . 107, 426 (1984). 21 . R . F . Code and W.F. Ramsey, Phys . Rev. A4, 1945 (1971) . 22. A . J . van der E s t , M . Y . Kok, and E . E . B u r n e l l , M o l . Phys . ( i n p r e s s ) . 23. J . W . Emsley, J . C . L i n d o n , NMR Spectroscopy U s i n g L i q u i d C r y s t a l s , Pergamon P r e s s , (1975). 24. A . J . van der E s t , p r i v a t e communication. 25. J . L o u n i l a and J . J o k i s a a r i , P r o g r . i n NMR S p e c t r o s c . 15, 249 (1982) . 26. N . H . W e r s t i u k , T. K a d a i , Can. J . Chem. 52, 2169 (1974). 27. P. K e l l e r and L . L i e b e r t , S o l i d S ta te P h y s i c s , 14, 20 (1978). 28. Kodak P u b l i c a t i o n No. J J - 1 4 , EASTMAN L i q u i d C r y s t a l P r o d u c t s , (1973) . 29. P. D i e h l , H . K e l l e r h a l s , E. L u s t i g , NMR B a s i c P r i n c i p l e s and Prog- r e s s 6, 1 (1972). 30. P . D i e h l , P . M . H e n r i c h s , and W. N i e d e r b e r g e r , M o l . Phys . 20, 139 (1971) . 31. T . C . Wong, E . E . B u r n e l l , and L . W e i l e r , Chem. Phys . L e t t . 50(2), 243 (1977). 32. M . S . Gopinathan and P . T . Narasimhan, J . Magn. Reson. 6, 147 (1972) . 33. R . C . Long, J r . , S . L . Baugheum, and J . H . G o l d s t e i n , J . Magn. Reson. 7, 253 (1972). 34. J . M . Read, J r . , C . T . M a t h i s , and J . H . G o l d s t e i n , Spec t roch im. A c t a 21, 85 (1965). 35. E . E . B u r n e l l and C . E . de Lange, M o l . Phys . 16(1), 95 (1969). 36. W.A. Thomas and G . E . G r i f f i n , Org . Magn. Reson. 2, 503 (1970). 37. J . G e r r i t s e n and C. Maclean, R e c u e i l , 91, 1393 (1972). 38. H . B . Evans, J r . , A . R . T a r p l e y , and J . H . G o l d s t e i n , J . Phys . Chem. 72(7), 2552 (1968). 39. P . D i e h l and C L . K h e t r a p a l , M o l . Phys . 15, 201 (1968). - 106 - 40. P. D i e h l , J . A m r e i n , H . B o s i n g e r , and F . M o i a , O r g . Magn. Reson. 1 8 ( 1 ) , 21 (1982). 41. J . M . Read, J r . , R.W. C r e c e l y , R . S . B u t l e r , J . E . Loemker, and J . H . G o l d s t e i n , T e t . L e t t . 10, 1215 (1968). 42. W.A. T a l l o n and G . B . S a v i t s k y , J . Magn. Reson. 9, 422 (1973). 43 . E . E . B u r n e l l and M . A . Sweeney, Can. J . Chem. 52(21) , 2565 (1974). 44. E . E . B u r n e l l , P . D i e h l , and W. N e i d e r b e r g e r , Can. J . Chem. 52, 151 (1974). 45. L . E . S u t t o n , Table o f I n t e r a t o m i c D i s t a n c e s , S p e c i a l P u b l i c a t i o n No. 11 , Chem. Soc. London, (1958). 46. B . Bak, D. C h r i s t e n s e n , W.B. D i x o n , L . Hansen-Nygaard, J . R . Andersen , and M. S c h o t l a n d e r , J . M o l . S p e c t r o s c . 9, 124 (1962). 47. B . Bak, D. C h r i s t e n s e n , L . Hansen-Nygaard, and J . R . Andersen , J . M o l e c . S p e c t r o s c . 7, 58 (1961). 48. B . Bak, L . Hansen-Nygaard, and J . R . Andersen, J . M o l e c . S p e c t r o s c . 2 , 361 (1958). 49 . O . L . S t i e f v a t e r , Z . N a t u r f o r s c h . 30a, 1765 (1975). 50. L . Nygaard, J . Bo jesen , T. Pedersen, and J . R . Andersen , J . M o l . S t r u c t . 2 , 209 (1968). 51. F . M i c h e l , H . Nery , G. Roussy, Compt. Rendu 278B, 203 (1974). 52. Harmony e t a l . , J . Phys . Chem. Ref . Data . 8, 717 (1979). 53. M. Onda and I . Yamaguchi, J . M o l e c . S t r u c t . 34, 1 (1976). 54. M. Onda, 0 . Ohash i , and I . Yamaguchi, J . M o l e c . S t r u c t . 31, 203 (1976) . 55. O . G . Batyukhnova, N . I . Sadova, L . V . V i l k o v , Y u . A . Pankrushev, J . M o l e c . S t r u c t . 97, 153 (1983). 56. J . T r o t t e r and C S . W i l l i s t o n , A c t a C r y s t . 21, 285 (1966). 57. A . B o n d i , J . Phys . Chem. 68, 441 (1964). 58. A . D . Buckingham, E . E . B u r n e l l , and C . A . de Lange, J . Amer. Soc. 90, 2972 (1968). 59. G. de Broukere , W.C. Nieuwpoort , R. B r o e r , and G. B e r t h i e r , M o l . Phys . 45, 649 (1982). - 107 - APPENDIX - 108 - APPENDIX Experimental order parameters of solutes dissolved i n 55 wt% 1132 at 301.4 K (the EBBA molecules i n the mixture were not deuterated) M o l e c u l e E x p e r i m e n t a l Order Parameter 1 TTF S x x 0.3320 (17) -0 .081 (3) S z z -0.2514 (17) 2 Furan S x x 0.0914 (1) Syy 0.0460 (3) S z z -0.1374 (2) 3 Thiophene S x x 0.0604 (1) Syy 0.0922 (4) S z z -0.1526 (3) 4 P y r i d i n e S x x 0.1178 (2) Syy 0.0444 (5) S z z -0.1622 (3) 5 2 , 6 - D i f l u o r o p y r i d i n e S x x 0.1640 (3) Syy 0.0379 (6) S z z -0.2019 (3) - 109 - Fluorobenzene s ^ 0.0513 (1) Syy 0.1411 (2) S z z -0.1924 (1) Iodobenzene S x x -0.0238 (3) Syy 0.2355 (7) S Z 2 -0.2117 (4) 1 .2- Dicyanobenzene S x x 0.0610 (10) Syy 0.1770 (22) S z z -0.2380 (12) 1 .3- D i n i t r o b e n z e n e S x x -0.1915 (21) Syy 0.0320 (4) S z z -0.2236 (14) 1.4- Dichlorobenzene S x x - 0 . 0 7 1 1 ( 1 ) Syy 0.3148 (4) S z z -0.2437 (3) 1,4-Dibromobenzene S x x -0.0988 (1) Syy 0.3465 (2) S z z -0.2477 (1)

Cite

Citation Scheme:

    

Usage Statistics

Country Views Downloads
France 10 0
Germany 4 2
China 3 75
United States 2 6
Ukraine 1 0
City Views Downloads
Unknown 15 2
Beijing 3 0
Mountain View 1 6
Ashburn 1 0

{[{ mDataHeader[type] }]} {[{ month[type] }]} {[{ tData[type] }]}

Share

Share to:

Comment

Related Items