Conformational analysis, spectroscopic and quantum chemical investigations of 2-bromo-3-nitroacetophenone

The stable geometry of the compound has been determined by conformational analysis. The relative stabilities of the different conformations were discussed. The complete vibrational assignment and analysis of the fundamental modes of the compound 2-bromo-3-nitroacetophenone (2B3NAP) were carried out using the experimental FTIR and FT-Raman data and quantum mechanical studies. The experimental vibrational frequencies were compared with the wavenumbers obtained theoretically from the DFT-B3LYP and B3PW91 calculations employing the standard 6-31G∗∗, high level 6-311++G∗∗, cc-pVTZ basis sets for optimised geometry of the compound. The potential energy distribution of the fundamental modes was also calculated by utilising Wilson’s FG matrix method. The electronic properties, HOMO and LUMO energies were measured by time-dependent TD-DFT approach. The charges of the atoms by natural bond orbital (NBO) analysis were determined by B3LYP/6-311++G∗∗ method. The effect of NO2 and Br groups on the configuration of keto group and the skeletal vibrations have been discussed.

► FTIR, FT-Raman and NMR investigations of 2-bromo-3-nitroacetophenone were carried out.
► The stable conformer is non-planar and >CO group (O11) is 29.8° out of plane of the benzene ring.
► The limits of the molecular electrostatic potential observed is ±9.938e × 10−3.
► The nO→πNO∗ interaction having stabilisation energy of 167.08 kJ mol−1.
► 1H and 13C NMR chemical shifts of the molecule were discussed.