Effect of steric factors on mesomorphic stability I. 4‐(4‐Substituted phenylazo)‐1‐naphthyl 4‐alkoxybenzoates

Abstract

Four homologous series belonging to the family of 4‐(4‐substituted phenylazo)‐1‐naphthyl 4‐alkoxybenzoates (I _a–d) (C _n H_{2 n +1}O–C₆H₄–COO–C₁₀H₆–N = N–C₆H₄–X) were prepared in which the 4‐ substituent (X) was varied between CH₃O, CH₃, Cl and NO₂; while, within each homologous series, the number of carbon atoms, n, was varied between 8 and 14. The compounds were characterized by infrared spectroscopy, ¹H NMR spectroscopy and elemental analysis. Their mesophase behaviour was investigated by differential scanning calorimetry and polarizing‐optical microscopy. The results are discussed in terms of mesomeric, polarizability, and steric effects. In each group of compounds bearing the same alkoxy group, attempts were made to correlate the mesophase–isotropic transition temperatures (T _c) with the polarizability anisotropy, Δα _x , of bonds to the small compact substituent X.