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Keywords:

  • vibrational dephasing;
  • polarized Raman study;
  • DFT calculation;
  • 2Cl-pyridine;
  • 3Cl-pyridine

Abstract

Raman 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[BOND]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[BOND]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.