Group dipole moments, nematics

The crystal structure of 4-butylphenyl-4 -butylbenzoyloxybenzoate was determined by Haase et al. [101]. The compound forms a nematic phase. The neighbouring phenyl rings of the molecule are twisted by 49 and 62°. The dipole moments of the carbonyloxy groups perpendicular to the long molecular axis are compensated to each other as much as possible. 

The combined effect of a dipole moment and a flexible tail, usually present in mesogens, has been addressed in a MC study of hard spherocyUnders with a terminal dipole moment and an ideal (no voliune) flexible end-group [240]. Adding a flexible tail to a hard core SC acts on the range of stability of the nematic phase in an antagonistic way to the terminal dipole... 

Polymer XXVI only forms the nematic phase, while polymer XXVII forms the smectic type of mesophase. The reasons for this difference should be looked for in the character of the conformational state of the mesogenic fragments, which results in different anisotropy of the polarizability of the side groups of the polymer. This is confirmed by the difference in the dipole moments x, found, for example, in polymers XXIV (p. = 3.7 D) and XXV (p. = 3.3 D). 

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