Vibrational, conformational and electronic structure investigations of α,α′-dibromo-o-xylene, α,α′-dibromo-m-xylene and α,α′-dibromo-p-xylene

The Fourier transform infrared (FTIR) and FT-Raman spectra of alpha,alpha'-dibromo-o-xylene (DBOX), alpha,alpha'-dibromo-m-xylene (DBMX) and alpha,alpha'-dibromo-p-xylene (DBPX) of the configuration BrCH2-C6H4-CH2Br have been recorded in the range 4000-400 and 4000-100 cm(-1), respectively. The conformational analysis of these compounds was performed. The complete vibrational assignment and analysis of the fundamental modes of the most stable conformer of the compounds were carried out using the experimental FTIR and FT-Raman data, and quantum mechanical studies. The observed vibrational frequencies were compared with the wavenumbers derived theoretically for the optimized geometry of the compounds from the DFT-B3LYP gradient calculations employing the standard 6-31G**, high level 6-311++G** and cc-pVTZ basis sets. The structural parameters and vibrational wavenumbers obtained from the OFT method are in good agreement with the experimental data. The potential energy distributions of the fundamental modes were also calculated with OFT force fields utilizing Wilson's FG matrix method. The effect of -CH2Br group on the skeletal vibrations has been discussed. (C) 2012 Elsevier B.V. All rights reserved.