Molecules of cyanobiphenyl CB5, CB8 widely used as liquid crystals. In the study of the mesotropic liquid crystalline phase of cyanobiphenyl TSB5 observed by infrared spectroscopy complex there is a compound contour strip stretching vibration of the cyanogroup. In this regard, it can be assumed that the band consists of several normal vibration frequencies with different maxima and intensities of the absorption bands. In this paper we calculate the values ​​of oscillation frequencies for individual molecules CB5, dimers and trimers CB5. The calculation results show the dependence of the frequencies of the stretching vibrations of the cyanogroup on the structure of dimers and trimers. In this regard, it can be assumed that the band consists of several normal vibration frequencies with different maxima and intensities of the absorption bands. This result is verified by computer simulations conducted in this work.