Energy profile, spectroscopic (FT-IR, FT-Raman and FT-NMR) and DFT studies of 4-bromoisophthalic acid

The stable conformer of 4−bromoisophthalic acid (BIPA) has been identified by potential energy profile analysis. All the structural parameters of 4−bromoisophthalic acid are determined by B3LYP method with 6-311++G**, 6−31G** and cc−pVTZ basis sets. The fundamental vibrations are analysed with the use of FT−IR (4000-400 cm−1) and FT−Raman (4000−100 cm−1) spectra. The harmonic vibrational frequencies are theoretically calculated and compared with experimental FTIR and FT−Raman frequencies. The 1H and 13C NMR spectra have been analysed and compared with theoretical 1H and 13C NMR chemical shifts calculated by gauge independent atomic orbital (GIAO) method. The electronic properties, such as HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) energies are determined by B3LYP/cc−pVTZ method. The electron density distribution and site of chemical reactivity of BIPA molecule have been obtained by mapping electron density isosurface with molecular electrostatic potential (MEP). Stability of the molecules arising from hyperconjugative interactions, charge delocalizations have been analysed by using natural bond orbital (NBO) analysis. The thermodynamic properties and atomic natural charges of the compound are analysed and the reactive sites of the molecule are identified. The global and local reactivity descriptors are evaluated to analyse the chemical reactivity and site selectivity of molecule through Fukui functions.