Structural, vibrational spectroscopic studies and quantum chemical calculations of 4-fluoro-3-methylphenol

The FTIR and FT-Raman vibrational spectra of 4-fluoro-3-methylphenol (FMP) have been recorded in the regions 4000-400 cm-1 and 4000-50 cm-1, respectively. The complete vibrational fundamental modes of the compound using the experimental FTIR and FT-Raman data have been analyzed on the basis of peak positions, relative intensities and quantum chemical studies. In the calculations performed to determine the optimum molecular geometry, harmonic vibrational frequencies, infrared intensities and Raman scattering activities, ab initio Hartree-Fock (HF) and Density functional theory (DFT/B3LYP) methods with 6-311++G(d,p) basis sets were used. The difference between the observed and scaled wavenumber values of most of the vibrational modes is very small. The normal modes are assigned with the help of total energy distribution (TED) analysis. Non-linear optical (NLO) behavior of FMP was investigated by determining of electric dipole moment, polarizability, and hyperpolarizability. The effects of frontier orbitals, HOMO and LUMO, transition of electron density transfer have been discussed. Decrease in HOMO and LUMO energy gap, explains the eventual charge transfer within the molecule which is responsible for the chemical reactivity of the molecule. Besides, Mulliken’s charges analysis, and several thermodynamic properties were performed.

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