Spectroscopic, structural and conformational investigations of the major constituent of the clove oil: Eugenol

Abstract

Molecular structures of the 12 possible conformers of eugenol were optimized at the B3LYP/6–311++G** level available with the Gaussian 09 software. IR and Raman spectra of eugenol were measured and analysed in light of the computed quantities. The interpretation of the IR spectrum in the OH stretching region suggested the existence of eugenol in the dimeric form. Five dimeric structures of the lowest energy monomeric conformer (C-I) were found to have energy difference below 300K. The complete observed IR and Raman spectra could be explained in terms of the computed spectra of the five lowest energy dimers of C-I. UV–vis absorption spectrum was measured in the range 200–600 nm and analysed with the help of computed parameters. Moreover, MEP plots and HOMO-LUMO analysis were carried out. Different computed quantities/ parameters for C-I and its 5 dimers are compared. In addition, barrier heights for different tops, thermodynamic functions and bioactive scores of the eugenol molecule were determined.