Theoretical investigations on molecular structure and IR frequencies of 4-n-nonyl-4′-cyanobiphenyl in light of experimental results

The molecular geometry and the vibrational frequencies of 4-n-nonyl-4′-cyanobiphenyl, C9H19-C6H4-C6H4-CN, (9CBP) in ground state have been calculated using density functional theory with B3LYP/6-31G** basis set. The optimized geometric bond lengths and bond angles are in good agreement with the X-ray data. The optimized geometry is closer to molecule-1 of the asymmetric unit in the crystal structure. The conformation of the molecule is somewhat different to that obtained from crystallography. The vibrational spectra of 9CBP, calculated by B3LYP/6-31G** method, reproduce vibrational wave numbers with an accuracy which allows reliable vibrational assignments. The molecule has been studied theoretically in the 400-3200 cm− 1 region and the assignments of all the observed bands have been made. The analysis of the IR spectra indicated some structure-spectra correlation.