Use of vibrational spectroscopy to study 1,3-dimethyl-5-nitrobenzene: A combined theoretical and experimental approach

Abstract

The FTIR and FT-Raman spectra of 1,3-dimethyl-5-nitrobenzene (DMNB) have been recorded in the range 4000‒400 cm⁻¹ and 3500‒100 cm⁻¹, respectively. The molecular structures, fundamental vibrational frequencies and intensity of the vibrational bands have been investigated and interpreted theoretically with the use of structural optimizations and normal coordinate force field calculations based on density functional theory (DFT) with 6-31G(d,p) basis set. The vibrational assignments have been made from potential energy distribution (PED). The theoretically simulated vibrational spectra of the molecule show excellent agreement with the experimental spectra. The hyper conjugative interaction energy (E⁽²⁾) and electron densities of donor (i) and acceptor (j) bonds have been calculated using NBO analysis. The electronic transition has been studied using UV-Visible analysis of the title molecule with B3LYP/6-31G(d,p) level of theory. The microscopic non-linear optical (NLO) behaviour of the title compound has also been calculated. In addition, the ¹H and ¹³C NMR chemical shifts values of DMNB in the ground state for B3LYP/6-31G(d,p) method have also been calculated using gauge independent atomic orbital (GIAO) method.