Peculiarities of the structure and intermolecular interactons in 4-n-ALKYL-4′-cyanobiphenyls studied by IR spectroscopy

Experimental and theoretical methods of IR spectroscopy have been used to study the peculiarities of the structure and of intermolecular interactions in the homologous series of 4-n-alkyl-4′-cyanobiphenyls (abbreviated to nCBs, where n is the number of carbon atoms in the alkyl radical). IR absorption spectra of nCBs (n = 4, 8, 9) were measured in the frequency range from 400 cm^?1 to 4000 cm^?1 and in the temperature range from 26° to 100°C, which corresponded to the crystalline, liquid crystalline and liquid states of the samples. The analysis of the measured spectra was performed with regard to available X-ray data on the structures of crystalline phases and to the theoretical modeling of IR spectra; a comparison with previously studied spectra of nCBs with n = 2 and 5 was made. Characteristic differences between the spectra of higher and lower homologues of nCBs were found. Changes in the conformation of nCB molecules with the change of temperature and the length of the alkyl radical are discussed.