Study of Intermolecular Hydrogen Bonding in p-n-Alkoxybenzoic Acids and Alkyl Aniline Homologous Series – Part I

Abstract

A homologous series of interhydrogen bonded complexes between p-n-alkoxybenzoic acids (nABA) and alkyl anilines were isolated. The mesogenic nABA (where n represents the alkoxy carbon number from 5 to 12 except 6) formed a hydrogen bond with liquid crystal intermediate 4-hexyl aniline. The homologous series mesogens are analyzed by polarizing optical microscope, differential scanning calorimetry (DSC), and FTIR studies. An interesting feature of these homologous series is the drastic reduction of the mesogenic temperatures and the occurrence of smectic ordering just above ambient temperature. The phase diagrams of the nABA and the homologous series were computed and compared, respectively. A critical observation in all the binary compounds of the present homologous series reveals that there exists a correlation between the alkyl chain length and mesogenic phases induced. Further some of the mesogens exhibit monotropic Smectic F and Smectic G transition. The hydrogen bond formation was evinced through FTIR spectral studies. Results of free nABA and the hydrogen bonded homologous series were discussed in the light of increment in alkoxy carbon number, mesogenic phases exhibited, and mesogenic thermal span.