FT-IR and FT-Raman spectroscopic investigation, computed vibrational frequency analysis and IR intensity and Raman activity peak resemblance analysis on 2-nitroanisole using HF and DFT (B3LYP and B3PW91) calculations

Fourier-transform Raman and infrared spectra of 2-nitroanisole are recorded (4000–100 cm−1) and interpreted by comparison with respective theoretical spectra calculated using HF and DFT method. The geometrical parameters with CS symmetry, harmonic vibrational frequencies, infrared and Raman scattering intensities are determined using HF/6-311++G (d, p), B3LYP/6-311+G (d, p), B3LYP/6-311++G (d, p) and B3PW91/6-311++G (d, p) level of theories. A detailed vibrational spectral analysis has been carried out and assignments of the observed fundamental bands have been proposed on the basis of peak positions and relative intensities. The results of the calculations have been used to simulate IR and Raman spectra for the molecule that showed good agreement with the observed spectra. The SQM method, which implies multiple scaling of the DFT force fields has been shown superior to the uniform scaling approach. The vibrational frequencies and the infrared intensities of the C–H modes involved in back-donation and conjugation are also investigated.

Graphical abstractFourier-transform Raman and infrared spectra of 2-nitroanisole are recorded (4000–100 cm−1) and interpreted by comparison with respective theoretical spectra calculated using HF and DFT method. The geometrical parameters with CS symmetry, harmonic vibrational frequencies, infrared and Raman scattering intensities are determined using HF/6-311++G (d, p), B3LYP/6-311+G (d, p), B3LYP/6-311++G (d, p) and B3PW91/6-311++G (d, p) level of theories. A detailed vibrational spectral analysis has been carried out and assignments of the observed fundamental bands have been proposed on the basis of literature. The results of the calculations have been used to simulate IR and Raman spectra for the molecule that showed good agreement with the observed spectra. The SQM method, which implies multiple scaling of the DFT force fields has been shown superior to the uniform scaling approach. The vibrational frequencies and the infrared intensities of the C–H modes involved in back-donation and conjugation are also investigated.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Owing to the wide application and properties of anisole, a complete vibrational study on 2-nitroanisole has been undertaken. ► The molecular structure of 2-NA in the ground state is computed by performing both ab initio HF and DFT/B3LYP/B3PW91 theory. ► Computed vibrational spectral IR intensities and Raman activities have been presented. ► The IR Intensity and Raman activity peak resemblance analysis have been made on the vibrational frequencies. ► The ideal estimation of frequencies by DFT (B3LYP/B3PW91) methods are presented in the paper.