Comparative studies of the infrared spectra of Ethyl benzoate (C9H10O2) and Ethyl m-chloro benzoate (C9H9ClO2 or 4-Chlorobenzoic acid) have been made. The spectra are interpreted with the aid of normal mode analysis following full structure optimization based on the DFT and HF method using 6-31G(d,p) basis sets combination. While making complete assignments of vibrational wave numbers some interesting observations in the vibrational spectra of these two molecules have been noticed. Following the quantum chemical calculation optimized geometries of the both molecules are predicted. The theoretical global minimum energy calculation helps to find the structural symmetries of the molecules.
