Density functional theory study of vibrational spectra: 9. Structures and vibrational assignments of dicyanobenzenes

摘要

Density functional theory BLYP and ab initio HF calculations have been carried out to investigate the structures and vibrationa! spectra of dicyanobenzenes. The calculated results are in good agreement with reliable experimental data and indicate thatthe benzene rings of all three isomers are only slightly distorted by the two cyano groups. Vibrational frequencies calculated by BLYP/6-31G force fields agree very well with experimental results, with a mean deviation of about 14 cm~(-1) for non-CH stretching modes. On the basis' of agreement between the calculated and observed results, assignments of the fundamental vibrational modes were examined and some reassignments were proposed. This study demonstrates that the density functional theory BLYP calculation is a powerful approach to understanding the vibrational spectra of organic compounds.