Structures, molecular orbitals and UV–vis spectra investigations on Br2C6H4: A computational study

Abstract

The dibromobenzenes (1,2-, 1,3- and 1,4-Br2C6H4) have been studied by theoretical methods. The structures of these species are optimized and the structural characteristics are determined by density functional theory (DFT) and the second order Møller–Plesset perturbation theory (MP2) levels. The geometrical structures of Br2C6H4 show a little distortion of benzene ring due to the substitution of highly electronegativity of bromine atoms. The electronegativity of bromine atoms in 1,4-Br2C6H4 is predicted to be more negative than 1,2- and 1,3-Br2C6H4. In addition, dipole moment and frontier molecular orbitals (FMOs) of these Br2C6H4 are performed as well. The 1,4-Br2C6H4 is slightly more reactive than 1,2- and 1,3-Br2C6H4 because of its small HOMO–LUMO energy gap. The simulated UV–vis spectra are investigated by time-dependent density functional theory (TD-DFT) approach, which are in excellent agreement with the available experimental value. Our calculations show that a few of absorption features are between 140nm and 250nm, which is in ultraviolet C range, and the red shift of 1,3- and 1,4-Br2C6H4 are predicted. Moreover, the UV absorption features of these Br2C6H4 in water or methanol are predicted to be more intense than in gas phase due to solvent effect.