This work has been digitalized and published in 2013 by Verlag Zeitschrift für Naturforschung in cooperation with the Max Planck Society for the Advancement of Science under a Creative Commons Attribution4.0 International License.

Dieses Werk wurde im Jahr 2013 vom Verlag Zeitschrift für Naturforschungin Zusammenarbeit mit der Max-Planck-Gesellschaft zur Förderung derWissenschaften e.V. digitalisiert und unter folgender Lizenz veröffentlicht:Creative Commons Namensnennung 4.0 Lizenz.

Nematic Liquid Crystals with High Positive Dielectric Anisotropy

M a g e d A . O s m a n *

B r o w n Boveri Research Center, Chemistry Group, CH-5405 Baden-Dättwil , Switzerland

Z. Naturforsch. 34b, 1092-1095 (1979); received March 23, 1979

Liquid Crystals, Nematic Phases, High Positive Dielectric Anisotropy,

Alkylamino-cyano-b iphenyls , Alkylamino-cyano-phenylbenzoates Alky lamino- and formyl a lkylamino-cyano Schif f 's base, biphenyl and phenylbenzoate

l iquid crystals were synthesized. The mesomorphic behaviour o f these compounds is described. The introduction of the formyl group in the higher homologues lead to the disappearance o f the mesophase. The alkylamino and formylalkylamino substituents are strong electron donating groups and lead to nematic phases with remarkably high posit ive dielectric anisotropy.

I n t e r e s t i n e l e c t r o o p t i c a l d i s p l a y s b a s e d o n t h e

t w i s t e d n e m a t i c e f f e c t [1] h a s l e a d t o a g r o w i n g

d e m a n d f o r n e m a t i c l i q u i d c r y s t a l s w i t h p o s i t i v e

d i e l e c t r i c a n i s o t r o p y . N o n - p o l a r o r a l m o s t n o n - p o l a r

n e m a t i c c o m p o u n d s o f t h e t y p e 1 w e r e f o u n d t o

p o s s e s s a v e r y s m a l l p o s i t i v e d i e l e c t r i c a n i s o t r o p y

(As = 0 . 0 5 - 0 . 5 ) [ 5 - 7 ] ,

X =-CH= N - |21 , - C 0 0 - 131,—N=N— |4|

1

N e m a t i c p h a s e s o f t h e S c h i f f ' s b a s e a n d p h e n y l -

b e n z o a t e t y p e w i t h l a r g e r A a w e r e s y n t h e s i z e d b y A . B o i l e r [8, 9] t h r o u g h r e p l a c e m e n t o f o n e o f t h e

a l k y l g r o u p s b y t h e c y a n o g r o u p w h i c h p o s s e s s a

l a r g e r d i p o l e m o m e n t ( — 4 D ) . T h e r e m a i n i n g a l k y l

g r o u p o n t h e o t h e r e n d o f t h e m o l e c u l e , w h i c h h a s a

d i p o l e m o m e n t o f -f- 0.3 D , w a s n o t c h a n g e d .

R e c e n t l y , G . G r a y [10] a n d R . E i d e n s c h i n k [ 1 1 ]

p r e p a r e d a n a l o g o u s n e m a t i c p h a s e s o f t h e b i p h e n y l

a n d p h e n y l c y c l o h e x a n e t y p e s . A l l t h e s e c o m p o u n d s

h a v e A e v a l u e s f r o m 8 t o 20 [ 1 2 - 1 4 ] w h i c h a l l o w a n o p e r a t i n g v o l t a g e o f 3 v o l t s f o r a t w i s t e d n e m a t i c

d i s p l a y . S i n c e t h e t h r e s h o l d v o l t a g e a n d , c o r r e s p o n d -

i n g l y , t h e o p e r a t i n g v o l t a g e is p r o p o r t i o n a l t o

\J11A e, i t is c l e a r t h a t n e w n e m a t i c l i q u i d c r y s t a l s w i t h l a r g e r d i e l e c t r i c a n i s o t r o p i c s a r e r e q u i r e d i f t h e

o p e r a t i n g v o l t a g e is t o b e s u b s t a n t i a l l y r e d u c e d .

T h i s c a n b e a c h i e v e d b y r e p l a c i n g t h e r e m a i n i n g

a l k y l g r o u p w i t h a n e l e c t r o n d o n a t i n g s u b s t i t u e n t

h a v i n g a s t r o n g e r d i p o l e m o m e n t a l o n g t h e m o l e c u -

l a r a x i s . T h e f i rs t a t t e m p t a l o n g t h i s l i n e w a s m a d e

b y i n t r o d u c i n g t h e d i m e t h y l a m i n o g r o u p ( - ( - 1 . 6 D )

* Reprint requests to Dr . M. A . Osman. 0340-5087/79/0800-1092/$ 01.00/0

a t t h e o t h e r e n d o f t h e b e n z y l i d e n - a m i n o b e n z o -

n i t r i l e m o l e c u l e , b u t t h i s g a v e a n i s o t r o p i c c o m -

p o u n d m e l t i n g a t 183 °C [15] . T h e d i s a p p e a r a n c e o f

t h e l i q u i d c r y s t a l l i n e p r o p e r t i e s is p r o b a b l y d u e t o

t h e h i g h m e l t i n g p o i n t o f t h i s c o m p o u n d a n d t o t h e

b u l k i n e s s o f t h e d i m e t h y l a m i n o g r o u p w h i c h l o w e r s

i t s c l e a r i n g p o i n t . T h e a i m o f t h i s w o r k is t o i n t r o d u c e

t h e less b u l k y m o n o a l k y l a m i n o g r o u p i n m o l e c u l e s

o f t y p e 1 a n d t o s t u d y t h e e f f e c t o f t h i s s u b s t i t u t i o n

o n t h e i r m e s o m o r p h i c b e h a v i o u r a n d o n t h e m a g n i -

t u d e o f t h e d i e l e c t r i c a n i s o t r o p y .

Results and Discussion

N - ( 4 - M e t h y l a m i n o b e n z y l i d e n e ) - 4 ' - a m i n o b e n z o -

n i t r i l e (2) w a s p r e p a r e d b y c o n d e n s i n g 4 - m e t h y l -

a m i n o b e n z a l d e h y d e w i t h 4 - a m i n o b e n z o n i t r i l e i n

b u l k [16].

CH3HN-̂ )-cho+H2N--CN-̂ CH3HN-Q>-CH-N^Q>-CN

z

T h e a l d e h y d e w a s p r e p a r e d b y t h e V i l s m e i e r re-

a c t i o n [17] .

2"c> ~ H j C : N C N H 0 ~ H 3 C H N < > CHO

C o m p o u n d 2 m e l t e d a t 1 6 3 . 1 °C a n d s h o w e d a

m o n o t r o p i c n e m a t i c p h a s e c l e a r i n g a t 138.0 °C.

T h i s c o n f i r m e d t h a t t h e d i s a p p e a r a n c e o f t h e m e s o -

p h a s e i n t h e d i m e t h y l a m i n o d e r i v a t i v e w a s c a u s e d

b y t h e b u l k i n e s s o f t h i s g r o u p . H o w e v e r , t h e m e l t i n g

p o i n t o f c o m p o u n d 2 is t o o h i g h f o r p r a c t i c a l

a p p l i c a t i o n s a n d f o r c o n v e n i e n t l y m e a s u r i n g t h e

d i e l e c t r i c a n i s o t r o p y . T h e h i g h e r h o m o l o g u e s o f

a l k y l a m i n o b e n z a l d e h y d e a n d t h e i r S c h i f f ' s b a s e s

w e r e t h e r e f o r e p r e p a r e d in a n a t t e m p t t o l o w e r t h e

m e l t i n g p o i n t . I t s e e m e d a l s o o f i n t e r e s t t o in-

M. A. Osman • Nematic Liquid Crystals 1093

* > - ® - C H - N - © - C N

X R TM [°C] Tc [°C] Gernerai C [ % ] H [ % ] N [ % ] formula calcd found calcd found calcd found

H CH3 163.2 138.0 C15H13N3 76.57 76.46 5.57 5.61 17.86 17.68 H C2H5 154.6 129.1 C16H15N3 77.08 77.02 6.06 6.04 16.86 16.86 H C3H7 151.7 — C17H17N3 77.53 77.51 6.51 6.55 15.91 15.96 H C4H9 129.6 — Ci8HI9N3 77.94 77.76 6.91 6.88 15.15 15.06 H C6H13 97.8 78.6 CsoHagNg 78.65 78.78 7.59 7.72 13.76 13.73 H C8H17 95.8 78.1 C22H27N3 79.24 79.36 8.16 8.28 12.60 12.45 CHO CH3 159.1 134.8 C16H13N3O 72.98 72.83 4.98 5.10 15.96 15.92 CHO C2H5 132.3 — C17H15N3O 73.63 73.49 5.45 5.55 15.15 15.00 CHO C4H9 81.2 — C19H19N3O 74.73 74.55 6.27 6.32 13.76 13.60

v e s t i g a t e t h e e f f e c t o f i n t r o d u c i n g t h e f o r m y l g r o u p

i n t h e a l k y l a m i n o S c h i f ' s b a s e s .

T h e m e l t i n g a n d c l e a r i n g p o i n t s o f t h e S c h i f f ' s

b a s e s a r e g i v e n i n T a b l e I .

A s i t w a s e x p e c t e d t h e m e l t i n g p o i n t s f e l l r a p i d l y

f r o m 1 6 3 . 1 °C t o 9 7 . 8 °C w i t h g r o w i n g c h a i n l e n g t h

u p t o CÖ- H o w e v e r , e x t e n s i o n o f t h e a l k y l c h a i n t o C 8 d i d n o t m a r k e d l y l o w e r t h e m e l t i n g p o i n t .

U n f o r t u n a t e l y t h e c l e a r i n g p o i n t s s u f f e r e d a s i m i l a r

d e c r e a s e s o t h a t a l l t h e s y n t h e s i z e d a l k y l a m i n o

S c h i f f ' s b a s e s s h o w e d o n l y m o n o t r o p i c n e m a t i c

p h a s e s . T h e n e m a t i c t o i s o t r o p i c t r a n s i t i o n t e m -

p e r a t u r e s i n t h i s s e r i e s a r e m u c h h i g h e r t h a n t h o s e

o f t h e c o r r e s p o n d i n g a l k y l d e r i v a t i v e s [9]. T h e

i n t r o d u c t i o n o f t h e f o r m y l g r o u p i n c o m p o u n d 2 d i d

n o t h a v e a s i g n i f i c a n t e f f e c t o n e i t h e r i t s m e l t i n g

p o i n t o r o n i t s c l e a r i n g p o i n t . H o w e v e r , i t d i d c a u s e

a r e m a r k a b l e d e c r e a s e o f t h e m e l t i n g p o i n t s as w e l l

a s o f t h e c l e a r i n g p o i n t s o f t h e h i g h e r h o m o l o g u e s s o

t h a t t h e m e s o m o r p h i c p r o p e r t i e s d i s a p p e a r e d i n

t h e s e c o m p o u n d s . T h e n e m a t i c p h a s e i n t h i s ser ies

w a s o n l y m o n o t r o p i c a n d t h e m e a s u r e m e n t s o f t h e

d i e l e c t r i c a n i s o t r o p y i n t h e s u p e r c o o l e d s t a t e w a s

p r a c t i c a l l y i m p o s s i b l e .

T h e c h e m i c a l l y m o r e s t a b l e 4 - a l k y l a m i n o - 4 ' -

c y a n o b i p h e n y l s w e r e p r e p a r e d a c c o r d i n g t o t h e

f o l l o w i n g s c h e m e :

jsn/HCl

T h e 4 - b r o m o - 4 ' - n i t r o b i p h e n y l w h i c h w a s o b t a i n e d

b y b r o m i n a t i n g 4 - n i t r o b i p h e n y l [18], w a s f i rs t

c o n v e r t e d t o t h e n i t r i l e d e r i v a t i v e [19] . T h e 4 - c y a n o -

4 ' - n i t r o b i p h e n y l w a s t h e n r e d u c e d b y S n / H C l [20]

t o t h e a m i n o d e r i v a t i v e a n d a l k y l a t e d w i t h t h e

c o r r e s p o n d i n g a l k y l i o d i d e i n t h e n o r m a l w a y . T h e

r e s u l t i n g m o n o a n d d i a l k y l d e r i v a t i v e s w e r e chro-

m a t o g r a p h i c a l l y s e p a r a t e d .

T h e m e l t i n g a n d c l e a r i n g p o i n t s o f t h e a l k y l a m i n o -

a n d a l k y l f o r m y l a m i n o - c y a n o b i p h e n y l s a r e g i v e n i n

T a b l e I I . A l l t h e m e m b e r s o f t h i s s e r i e s s h o w

n e m a t i c p h a s e s w h i c h a r e t h e r m o d y n a m i c a l l y m o r e

s t a b l e t h a n t h e c o r r e s p o n d i n g a l k y l d e r i v a t i v e s [10]

( F i g . 1). T h e f i rs t t h r e e m e m b e r s s h o w e d a n u n u s u a l

s h a r p d e c r e a s e i n b o t h t h e m e l t i n g a n d t h e c l e a r i n g

p o i n t s w i t h g r o w i n g a l k y l c h a i n l e n g t h a n d a r e

m o n o t r o p i c l i q u i d c r y s t a l l i n e . T h e n e m a t i c - i s o t r o p i c

t r a n s i t i o n s o f t h e h i g h e r h o m o l o g u e s f o l l o w t h e

u s u a l a l t e r n a t i n g o d d - e v e n e f f e c t w i t h a d e c r e a s i n g

t e n d e n c y . T h e m e l t i n g p o i n t s h o w e d a s i m i l a r a l t e r -

n a t i o n b u t w i t h a h i g h e r a m p l i t u d e s o t h a t t h e

p e n t y l , o c t y l a n d n o n y l d e r i v a t i v e s h a d e n a n t i o -

t r o p i c n e m a t i c p h a s e s . T h e s h a r p d e c r e a s e i n t h e

c l e a r i n g p o i n t s o f t h e f i rs t t h r e e m e m b e r s o f t h e

ser ies c o u l d b e e x p l a i n e d o n t h e b a s i s o f h y d r o g e n

b o n d s w h i c h m a y s t e r i c a l l y h i n d e r t h e f r e e r o t a t i o n

o f t h e a l k y l c h a i n . I n t r o d u c i n g t h e f o r m y l g r o u p i n

t h e s e c o m p o u n d s a l s o c a u s e d a m a r k e d d e p r e s s i o n

i n b o t h m e l t i n g a n d c l e a r i n g t e m p e r a t u r e s . T h e

n e m a t i c p h a s e c o u l d o n l y b e o b s e r v e d i n t h e m e t h y l

f o r m y l a m i n o d e r i v a t i v e . T h i s is p r o b a b l y b e c a u s e

t h e f o r m y l g r o u p s t e r i c a l l y f o r c e s t h e a l k y l g r o u p

o u t o f t h e p l a n e o f t h e m o l e c u l e t h u s d e c r e a s i n g i t s

g e o m e t r i c a l a n i s o t r o p y .

T h e d i e l e c t r i c a n i s o t r o p i e s o f t h e p e n t y l a n d o c t y l

d e r i v a t i v e s w e r e m e a s u r e d a t a r e d u c e d t e m p e r a t u r e

o f 0.96 ( T a b l e I I I ) . I t c a n b e s e e n f r o m T a b l e I I I

t h a t 4 - c y a n o - 4 ' - 7 i - p e n t y l a m i n o b i p h e n y l p o s s e s s a

d i e l e c t r i c a n i s o t r o p y w h i c h is t w o a n d a h a l f t i m e s

l a r g e r t h a n 4 - c y a n o - 4 ' - 7 i - h e x y l b i p h e n y l a t t h e s a m e

r e d u c e d t e m p e r a t u r e .

1094 M. A . Osman • Nemat ic L iquid Crystals

Table I I .

X R T M [°C] TC [°C] General C [ % ] H [ % ] N [ % ] formula calcd found calcd found calcd f o u n d

H CH 3 199.2 180.0 C14H12N2 80.74 80.76 5.81 5.91 13.45 13.31 H C2H5 180.4 139.9 C15H14N2 81.05 81.08 6.35 6.40 12.60 12.51 H C3H7 106.4 100.2 C16H16N2 81.32 81.27 6.83 6.82 11.86 11.84 H C4H9 113.6 101.7 CI7HIGN2 81.56 81.47 7.25 7.27 11.19 11.12 H C5H11 86.3 90.7 C i 8H 2 ON 2 81.78 81.71 7.63 7.64 10.60 10.62 H C6H13 105.3 93.8 C19H22N2 81.97 81.98 7.97 7.93 10.06 10.00 H C7H15 92.2 89.0 C2oH2 4N2 82.14 82.26 8.27 8.32 9.58 9.55 H C8H17 81.4 91.8 C21H26N2 82.31 82.29 8.55 8.57 9.14 9.10 H C9H19 83.9 89.8 C22H28N2 82.45 82.60 8.81 8.85 8.74 8.77 C H O CH 3 127.0 84.4 C15H12N2O 76.25 76.27 5.12 5.24 11.86 11.92 C H O C2H5 106.2 — C I 6 H I 4 N 2 0 76.78 76.77 5.64 5.73 11.19 11.25 C H O C9H19 50.9 — C23H28N2O 79.27 79.24 8.10 8.14 8.04 8.04

190

Tc

t °C

150

100

7 5

50

"I 1 1 1 1 1 1 T

CnH2n + 1 N H - 0 - 0 - C N

\ J 1 I I 1 I I I

n+1

- • C n H 2 n + 1 ^ Q - 0 - C N

Fig. 1. Clearing points o f alkyl- and a lkylamino-cyano-biphenyls.

Table I I I .

1 el Ae

4 -n -Pentylamino - 4 ' - cy anobipheny 1 4 -n -Octy lamino-4 ' - cyanobiphenyl 4 -n -Hexy l -4 ' - cyanob ipheny l

36.8 30.7 17.4

9.8 8.1 6.6

27.0 22.6 10.8*

4 - w - H e x y l - 4 ' - c y a n o p h e n y l - b e n z o a t e h a s a A e o f

2 1 . 7 c o m p a r e d t o 10.8 f o r 4 - c y a n o - 4 ' - n - h e x y l b i -

p h e n y l a t t h e s a m e r e d u c e d t e m p e r a t u r e . T h i s

i n c r e a s e is c a u s e d b y t h e d i p o l a r c o n t r i b u t i o n o f t h e

c a r b o x y l g r o u p . I t is t h e r e f o r e t o b e e x p e c t e d t h a t

t h e a l k y l a m i n o - c y a n o p h e n y l b e n z o a t e s w i l l p o s s e s s

m u c h h i g h e r d i e l e c t r i c a n i s o t r o p i e s . T h e s e c o m -

p o u n d s w e r e s y n t h e s i z e d a s f o l l o w s :

0ZN-OC0CI + H0-©>-CN 0j,N-(Q-C0-CN

Zn CH.COOH

* B D H .

T h e 4 - n i t r o - 4 ' - c y a n o p h e n y l b e n z o a t e , o b t a i n e d b y

e s t e r i f i c a t i o n o f 4 - n i t r o b e n z o y l c h l o r i d e i n p y r i d i n e

i n t h e u s u a l w a y , w a s first r e d u c e d t o t h e c o r -

r e s p o n d i n g a m i n o e s t e r [20]. T h e a l k y l a m i n o e s t e r s

w e r e t h e n o b t a i n e d b y r e d u c t i v e a l k y l a t i o n o f t h e

a m i n e a c c o r d i n g t o t h e m e t h o d d e s c r i b e d b y A .

S u r r e y [21] ,

T h e t r a n s i t i o n t e m p e r a t u r e s o f t h e s e c o m p o u n d s

a r e g i v e n i n T a b l e I V . A l l t h e s y n t h e s i z e d p r o d u c t s

s h o w e d t h e r m o d y n a m i c a l l y m o r e s t a b l e n e m a t i c

p h a s e s t h a n t h e c o r r e s p o n d i n g a l k y l d e r i v a t i v e s a n d

n o s e m a t i c p h a s e s c o u l d be o b s e r v e d ( F i g . 2). A s

i n t h e b i p h e n y l ser ies , t h e first t h r e e m e m b e r s

s h o w e d a n u n u s u a l s h a r p d e c r e a s e o f t h e c l e a r i n g

p o i n t s w i t h g r o w i n g a l k y l c h a i n l e n g t h . F r o m C3

u p w a r d s t h e t r a n s i t i o n t e m p e r a t u r e s a l t e r n a t e d i n

t h e u s u a l w a y a n d r e m a i n e d b e t w e e n 89 °C a n d

84 °C w h i c h is a b o u t 10 °C l o w e r t h a n t h e cor-

r e s p o n d i n g b i p h e n y l d e r i v a t i v e s . T h i s b e h a v i o u r is

i n c o n t r a s t t o t h e a l k y l d e r i v a t i v e s w h e r e t h e e s t e r s

p o s s e s s h i g h e r c l e a r i n g p o i n t s . T h e m e l t i n g t e m -

M. A. Osman • Nematic Liquid Crystals 1095

Table IV. W

X R T m [ °C ] T c [ °C] General C [ % ] H [ % ] N [ % ] formula calcd found calcd found calcd found

H CH3 184.9 145.9 CI5H12N202 71.41 71.25 4.80 4.79 11.11 11.04 H C2H5 171.5 127.1 C16H14N2O2 72.16 72.16 5.30 5.31 10.52 10.43 H C3H7 169.0 84.9 C17H16N2O2 72.84 72.79 5.75 5.79 9.99 9.83 H C4H9 141.3 89.1 C18H18N2O2 73.45 73.35 6.16 6.16 9.52 9.37 H C5H11 108.4 77.3 C19H20N2O2 74.00 73.96 6.59 6.59 9.09 9.10 H C6H13 117.7 84.5 C20H22N2O2 74.50 74.45 6.88 6.91 8.69 8.67 H C7H15 117.3 81.2 C2IH24N202 74.97 74.96 7.19 7.22 8.33 8.34 H C8H17 118.5 82.0 C22H26N202 75.40 75.50 7.48 7.53 7.99 8.01 CHO CH3 173.2 116.2 C16H12N2O3 68.56 68.69 4.32 4.46 10.00 10.02 CHO C2H5 109.4 — C17H14N2O3 69.37 69.34 4.80 4.79 9.52 9.51 CHO C5H11 43.5 — C20H20N2O3 71.41 71.43 5.99 6.03 8.33 8.45 CHO C6H13 52.2 — C21H22N2O3 71.98 71.86 6.33 6.35 8.00 8.07

1 5 0 TC

t

100

3 0 0 1 2 3 4 5 6 7 8 9 Fig. 2. Clearing points of alkyl- and alkylamino-cyano-phenylbenzoates.

[1] M. Schadt and W. Helfrich, Appl. Phys. Lett. 18, 127 (1971).

[2] M. A. Osman, Z. Naturforsch. 31b, 801 (1976). [3] R. Steinsträsser, Z. Naturforsch. 27b, 774 (1972). [4] J. van der Veen, W. H. de Jeu, A. H. Grobben,

and J. Boven, Mol. Cryst. Liq. Cryst.17,291(1972). [5] R. T. Klingbiel, D. J. Genova, T. R. Criswell, and

J. P. van Meter, J. Am. Chem. Soc. 96 (25), 7651 (1974).

[6] W. H. de Jeu and Th. W. Lathouwers, Mol. Cryst. Liq. Cryst. 26, 225 (1974).

[7] W. H. de Jeu and Th. Lathouwers, Z. Natur-forsch. 29a, 909 (1974).

[8] A. Boller and H. Scherrer, German patent disclosure 2306739 (1973).

[9] A. Boller and H. Scherrer, German patent disclosure 2306738 (1973).

[10] G. W. Gray, K. J. Harison, J. A. Nash, J. Constant, D. S. Hulme, J. Kirton, and E. P. Raynes, Liquid Crystals and Ordered Fluids, vol. 2, 617 (1974).

p e r a t u r e s o f t h e s e p r o d u c t s w e r e g e n e r a l l y h i g h e r

t h a n t h e c o r r e s p o n d i n g b i p h e n y l s so t h a t t h e

n e m a t i c p h a s e s w e r e o n l y m o n o t r o p i c . T h e d i e l e c t r i c

a n i s o t r o p i c s c o u l d t h e r e f o r e n o t be m e a s u r e d . T h e s e

a l k y l a m i n o b e n z o a t e s a r e e s t i m a t e d t o possess a A e o f m o r e t h a n 40. T h e i n t r o d u c t i o n o f t h e f o r m y l

g r o u p in t h i s t y p e o f c o m p o u n d h a d t h e s a m e e f f e c t

a s in t h e S c h i f f ' s b a s e s a n d t h e b i p h e n y l s .

Experimental A l l s u b s t a n c e s w e r e i n v e s t i g a t e d b y p o l a r i z i n g

m i c r o s c o p y a n d b y d i f f e r e n t i a l s c a n n i n g c a l o r i m e t r y ( D S C ) . T h e m i c r o s c o p i c o b s e r v a t i o n s w e r e m a d e u n d e r a L e i t z O r t h o p l a n m i c r o s c o p e u s i n g a M e t t l e r F P 52 h o t - s t a g e . T h e t r a n s i t i o n t e m p e r a t u r e s w e r e d e t e r m i n e d w i t h a n a c c u r a c y o f ± 0.1 °C. T h e p u r i t y o f t h e p r o d u c t s w a s > 9 9 . 7 % as d e t e r m i n e d b y G L C .

T h e a u t h o r is g r a t e f u l t o D r . J . N e h r i n g f o r m e a s u r i n g t h e d i e l e c t r i c a n i s o t r o p y .

[11] R. Eidenschink, D. Erdmann, T. Krause, and L. Pohl, Angew. Chem. 89, 103 (1977).

[12] L. Pohl, R. Eidenschink, G. Krause, and D. Erd-mann, Phys. Lett. 60 A, 421 (1977).

[13] A. Boller, M. Cereghetti, M. Schadt, and H. Scherrer, Mol. Cryst. Liq. Cryst. 42, 215 (1977).

[14] P. G. Cummins, D. A. Dunmur, and D. A. Laidler, Mol. Cryst. Liq. Cryst. 30, 109 (1975).

[15] J. A. Castellano, J. E. Goldmacher, L. A. Barton, and J. S. Kane, J. Org. Chem. 33, 3501 (1968).

[16] M. A. Osman, German patent disclosure 2443618 (1976).

[17] Houben-Weyl VII/1, 30 (1954). [18] R. Le Fevre and E. Turner, J. Chem. Soc. 1926,

2041. [19] G. W. Gray and A. Mosley, J. Chem. Soc. Perkin

Trans. 2, 97 (1976). [20] A. J. Hill and M. V. Cox, J. Am. Chem. Soc. 48,

3218 (1926). [21] A. R. Surrey and H. F. Hammer, J. Am. Chem.

Soc. 66, 2127 (1944).

• - A / - -i i i i i f

n + 1 o

CnH2n+1-O-C-0Hn)-CN

-

J I I I I I I I