Conformational, structural and vibrational studies of estragole

[Display omitted] •Estragole is found to have only three conformers.•Fermi resonance between modes [νs(CH2) and 2 βs(CH2)] and modes [νs(CH3) and 2 δs(CH3)] gives rise to the same frequency doublet in IR and Raman spectra.•The barrier heights for different tops are high enough to prevent conversion of one conformer into another.•Out of 63 modes, 30 modes were found to be conformer dependent.•The sites of the nucleophilic attack are near O atom in conformers II/III and C3 atom in conformer I. Structural and conformational investigations were carried out at the B3LYP/6-311++G** level using the Gaussian 09 software. Vibrational spectra along with other related parameters like molecular geometries; APT charges etc were computed to analyze the experimentally measured Raman and IR spectra. In order to interpret the experimental spectra the potential energy distributions were computed using the GAR2PED software. Barrier heights for the OCH3, CH2CHCH2 and CHCH2 tops were estimated using the DFT and single top rotor theories. Vibrational contributions to the thermodynamic functions, namely, specific heat, entropy and free energy were determined. MEP, ESP plots and HOMO-LUMO energies were calculated using the results of the optimized structures of the three conformers of the estragole molecule. UV-vis spectrum was also investigated and interpreted. Comparative structural, active sites and vibrational investigations were made for all the three conformers.