The Effect of Carbonyl Containing Terminal Chains on Mesomorphic Properties in 4,4′-Disubstituted Phenylbenzoates and Phenylthiobenzoates. 5. Phenylbenzoates Containing a (CH₂)_n0₂CR′ Group (n=1,2) on the Phenolic End

Abstract

A few homologs of the esters 2 (R′=C₈H₁₇, n=1 or 2) and 4 (R′=C₇H₁₅)

1 Y=(CH₂)_nCO₂R′, n=0-2

2 Y=(CH₂)_nOCOR′, n=0-2

3 Y=O(CH₂)_nCO₂R′, n=l,2

4 Y=O(CH₂)_nOCOR′, n=2

were synthesized and their mesomorphic properties determined using hot-stage polarizing microscopy. No mesophases were observed for series 2 (n=1) or 4. This was also true for the previously reported series 1 (n=1) and 3. Transition temperatures for series 2 with n=2 were lower than when n=1 but higher than for the reverse ester series 1 with n=2. In both series 1 and 2 with n=2, only short range monotropic phases were observed. Like its parent series 2 (n=0), the n=2 esters showed various combinations of nematic and smectics A, B and C, whereas the reverse esters 1 (n=2) have only nematic and smectic A phases.

The phenols required for synthesizing the esters 2 (n=2) and 4 were prepared from the analogous protected phenolic alcohols. No suitable protecting group which could be selectively removed from the phenol could be found for synthesizing the precursor alcohol for series 2 when n=1. Instead these esters were prepared by esterification of the appropriately 4-substituted benzoic acid with 4-hydroxy-benzaldehyde, reduction to the alcohol and esterification. NMR spectra were used to confirm the structures of all intermediates and esters.

Key Words:

• liquid crystals
• phenylbenzoates
• 4-substituted phenols
• NMR