Density functional theory, comparative vibrational spectroscopic studies, HOMO–LUMO, first hyperpolarizability analyses of 2-fluoro 5-nitrotoluene and 2-bromo 5-nitrotoluene

This work deals with the vibrational spectra of 2-fluoro 5-nitrotoluene and 2-bromo 5-nitrotoluene by quantum chemical calculations. The solid phase FTIR and FT-Raman spectra of the title compounds were recorded in the regions 4000–400 cm−1 and 4000–50 cm−1 respectively. The spectra were interpreted with the aid of normal co-ordinate analysis based on density functional theory (DFT) using standard B3LYP/6-31G* basis set for the most optimized geometry. The vibrational frequencies are calculated and scaled values are compared with experimental FTIR and FT-Raman spectra. The scaled theoretical wave numbers showed very good agreement with the experimental ones. The complete vibrational assignments are performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanical (SQM) method. 13C and 1H NMR chemical shifts results are compared with the experimental values.

Graphical abstractIn this work, we reported a combined experimental and theoretical study on molecular structure, vibrational spectra, hyperpolarizability, HOMO, LUMO, NMR analysis of 2-fluoro 5-nitro toluene and 2-bromo 5-nitro toluene.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Simulated and observed vibrational spectra are agreed well. ► 1H and 13C NMR chemical shifts have been compared with experimental values. ► Polarizability, hyperpolarizability and total dipole moment have been calculated. ► The HOMO–LUMO energy gap of FNT and BNT are 0.182 a.u and 0.172 a.u.