Density functional theory investigations on the conformational stability, molecular structure and vibrational spectra...

The Fourier-transform infrared and FT-Raman spectra of 6-methyl-2-chromenone (6M2C) was recorded in the region 4000-400 cm(-1) and 3500-50 cm(-1) respectively. Quantum chemical calculations of energies, geometrical structure and vibrational wavenumbers of 6M2C were carried out by density functional theory (DFT/B3LYP and LSDA) method with 6-311++G(d,p) basis set. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. The values of the total dipole moment (μ) and the first order hyperpolarizability (β) of the investigated compound were computed using B3LYP/6-311++G(d,p) calculations. The calculated results also show that 6M2C might have microscopic non-linear optical (NLO) behaviour with non-zero values. A detailed interpretation of infrared and Raman spectra of 6M2C is also reported. The calculated HOMO-LUMO energy gap shows that charge transfer occur within the molecule. The molecular electrostatic potential map shows that the negative potential sites are on the electronegative atoms as well as the positive potential sites are around the hydrogen atoms. The NMR spectrum is used in conjunction with other forms of spectroscopy and chemical analysis to determinate the structures of complicated organic molecules.