Intra- and intermolecular interactions in mesogenic cyano compounds

In order to elucidate the intra- and intermolecular interactions, FTIR spec tra were measured on dilute solutions of CCl4 (0.01 mol l(-1)) and bulk sta tes from crystals to isotropic liquids for mesogenic 4-cyano-4'-alkylbiphen yls (nCB), 4-cyano-4'-alkoxybiphenyls (nOCB), 4-cyanophenyl 4-alkoxybenzoat es (CPnOB), and 4-alkoxyphenyl 4-cyanobenzoates (nOPCB) series. CN stretchi ng vibration frequencies in dilute solutions are slightly but definitely di fferent-0.5 cm(-1) higher for nCB than for nOCB and 0.8 cm(-1) higher for n OPCB than for CPnOB-giving a direct evidence of the different intramolecula r interaction of molecules. The frequency difference in mesophases is large r than that of molecules in solutions, 1.0 and 1.5 cm(-1) for cyanobiphenyl s and cyanoesters, respectively. The difference is related to the different extents of molecules overlapping, leading to the conclusion that the large r electron densities of CN groups in nOCB and CPnOB led to the larger overl apping of core moieties. A relationship between the wavenumbers and arrange ments of CN groups in crystals is pointed out.