Spectroscopic (FT-IR, FT-Raman and NMR) and NBO analysis of 3, 4-dimethylanisole by density functional method

Abstract

Combined experimental and theoretical studies have been conducted on the molecular structure and vibrational, spectra of 3, 4-dimethyl anisole (DMA). The FT-IR and FT-Raman spectra of DMA have been recorded in the solid phase. The molecular geometry and vibrational frequencies of DMA in the ground state have been calculated by using the ab-initio Hartree-Fock (HF) and density functional methods (B3LYP) invoking 6-31+G (d,p) basis set. The optimized geometric bond lengths and bond angles obtained by HF method shows best agreement with the experimental values. Comparison of the observed fundamental vibrational frequencies of DMA with calculated results by HF and density functional methods indicates that B3LYP is superior to the scaled HF approach for molecular vibrational problems. The difference between the observed and scaled wave number values of most of the fundamental is very small. The thermodynamic functions and atomic change of the title compound has also been performed at HF/B3LYP/6-31+G(d,p) level of theories. A detailed interpretation of the FT-IR, FT-Raman, NMR spectra of DMA has also been reported. The theoretical spectrograms for infrared and Raman spectra of the title molecule have been constructed. The thermodynamic function of the title compound has also been performed at HF/6-31+G (d,p) and B3LYP/6-31+G (d,p) level of theories. Natural bond orbital analysis has been carried out to explain the change transfer or delocalization of change due to the intra-molecular interactions. Energy of the highest occupied molecular (HOMO) orbital and lowest unoccupied (LUMO) molecular orbital have been predicted.