Vibrational Assignments and Electronic Structure Calculations for 3-Chloro-4-Hydroxybenzaldehyde

Abstract

Fourier‐Transform Laser Raman (3500‐50 cm−1) and Infrared (4000‐400 cm−1) spectral measurements have been made for the solid 3‐Chloro‐4‐hydroxybenzaldehyde. Electronic ground state energy, equilibrium structure, harmonic vibrational frequencies, depolarization ratios, force constants and normal modes have been computed at two levels of theory, namely, Restricted Hartree‐Fock (RHF) and Becke’s three parameter‐hybrid functional combined with Lee‐Yang‐Parr correlation (B3LYP) combined with 6‐31G* basis set. Potential energy distributions (PEDs) and normal mode analysis have been performed. The orientation of C=O of aldehydic group with respect to the hydroxyl group and chlorine in the Cis form is found to be the most stable. Of the aldehydic frequencies, the C=O stretching vibration observed at 1670 cm−1 is predicted at 1727 cm−1; the C–H vibration observed at 2751 cm−1 is predicted at 2798 cm−1. A broad IR band near 3180 cm−1 shows the evidence of hydrogen bonding, O–H…O. A good agreement between theoretical and experimental spectra is observed. A complete assignment of the observed spectra, aided by the theoretical results and normal modes has been proposed.