Vibrational study, molecular properties and first-order molecular hyperpolarizability of Methyl 2-amino 5-bromobenzoate using DFT method

Abstract

The molecular structure of Methyl 2-amino 5-bromobenzoate (M2A5B) was investigated by density functional theory employing Becke’s three parameter hybrid exchange functional with Lee–Yang–Parr (B3LYP) co-relational functional involving 6-311++G(d,p) basis set. Harmonic vibrational wavenumber calculation along with the normal mode analysis has been carried out in order to obtain a complete description of molecular dynamics. A detailed interpretation of the Infrared and Raman spectra of M2A5B have been reported. Complete vibrational assignments of the vibrational modes have been done on the basis of the potential energy distribution (PED) in terms of internal coordinates. The scaled vibrational wavenumbers corrected by a recommended set of scaling factors were compared with the experimental results and a fairly good agreement was obtained. The molecular electrostatic potential mapped onto total density surface has been obtained. A study on the electronic properties, such as absorption wavelength, excitation energy and frontier molecular orbitals energy, was performed by time dependent DFT (TD-DFT) approach. Additionally, major contribution from molecular orbitals to the electronic transition was investigated theoretically. The stability of the molecule arising from hyper conjugative interactions and accompanying charge delocalization has been analyzed using natural bond orbital (NBO) analysis. The theoretical 1H and 13C NMR chemical shifts have been calculated by GIAO method and compared with experimentally measured ones. The polarizability and first order hyperpolarizability of the title molecule were calculated and interpreted. The energy gap between frontier orbitals has been used along with electric moments and first order hyperpolarizability, to understand the non linear optical (NLO) activity of the molecule. The prominent vibrational modes contributing to the NLO activity have been identified and examined from the concurrent IR and Raman activity. Thermodynamic properties (heat capacity, entropy and enthalpy) of the title compound at different temperatures have been calculated.