Preparation and Thermodynamics of Some Homologous Nitrones, a New Group of Liquid Crystals

To investigate the mesomorphic behavior of aldonitrones, a series of 13 homologs of N-(p-alkoxyphenyl)-α-anisylnitrones was prepared and characterized. Although most of these substances exhibit normal nematic or smectic mesophases, the trend in nematic-isotropic transition temperatures to increase as a function of alkoxy chain length is an exceptional occurrence. Comparison of our data with that of analogous compounds previously reported indicates that thermal persistence of the nematic phase of these compounds increases in the following order: 4,4′-dialkoxybenzylideneaniline, 4,4′-dialkoxyazobenzene, N,α-di-(4-alkoxyphenyl)-nitrone, 4,4′-dialkoxyazoxybenzene. In addition, the phase transitions were investigated by means of differential scanning calorimetry. The entropies of the mesophase-isotropic transitions of the nitrones imply that the long alkoxy chains, in contrast to a widely held belief, are not restricted to a single conformation in the mesophase.