Influence of alkyl chain length on the FTIR spectra of alkyl-cyanobiphenyls compounds

Fourier transform IR spectra of flexible biphenyl molecules as well as their 4-n-alkyl-4'-cyanobiphenyl derivatives with 2, 3, 4, 5, 6 and 7 carbon in alkyl chain, all in solid crystalline state in KBr pellet, were investigated. In order to determine and characterize all vibrations in the range of 400-4000 cm-1, Fourier transform IR spectrosocpy were applied. The different number of bands, their shapes and frequencies for alkyl-cyano-derivatives of biphenyl has been found. But the most essential changes were observed in the range 800-900 cm-1 and 2700-3000 cm-1. Few bands have been found in these regino while biphenyl does not display any bands in these two regions. It is shown that the changes observed in the spectra are not directly dependant on the relation of aromatic cyano core and length of the alkyl tail of the molecule.