Study of vibrational dephasing of CCl stretching mode of 2Cl‐pyridine and 3Cl‐pyridine in methanol environment by polarized Raman study and DFT calculations

Abstract

AbstractRaman spectra of [2Cl‐pyridine (2Cl‐p) + methanol] and [3Cl‐pyridine (3Cl‐p) + methanol] mixtures were recorded in the region 360–480 cm−1 and the concentration dependence of linewidths and peak positions of the isotropic part of the Raman scattered radiation for the CCl stretching mode were studied in the light of the existing models. The analysis of the results revealed that concentration fluctuation and diffusion simultaneously play a role in the dephasing of the CCl stretching mode. The optimized structures of the reference systems, 2Cl‐p and 3‐Cl‐p, and their various complexes with methanol were calculated by density functional theory (DFT) geometry optimization technique using B3LYP functional and 6–31 + G(d,p) basis set. On the basis of the results of geometry optimization and energy minimization calculation, we propose that the complex formed as a result of hydrogen bonding of one 3Cl‐p molecule with three methanol molecules is more stable than the one formed by one 3Cl‐p molecule and two methanol molecules. This study presents an explanation of changes in spectral features of ortho/meta Cl‐substituted pyridines supported by DFT derived optimized geometries. Equilibrium constants have been obtained from the spectral data for one of the systems (2Cl‐pyridine + methanol). Copyright © 2006 John Wiley & Sons, Ltd.