Abinitio study on radical anions of nitro compounds

Abstract

The results of abinitio molecular orbital calculations on some nitro compounds, RNO2 (R = CH3, CF3, CH2F, BH2, BF2, BHF, C6H5) and on the corresponding radical anions are reported. The geometries of the neutral and charged species were optimized at the SCF and MP2 levels of theory employing the 6-31G* and the 6-31 + G* basis sets. The rotation about the CN and BN bonds reveals distinct conformations for each molecule and vibrational frequencies were determined for such structures. All the employed levels of theory predict structural differences between neutral and charged molecules. The major geometrical changes occurring by electron adding to RNO2 consist in the lengthening of the NO bonds and in the shortening of the CN and BN bonds. The radical anions are calculated to be pyramidal at nitrogen in the stable conformers of CH3NO2−, CF3NO2−, CH2FNO2−, while, for the π-electron-accepting substituents (BH2, BHF, BF2, C6H5), the anion is planar. Electron correlation energy corrections in the framework of Møller–Plesset perturbation theory were included to determine relative stabilities between different conformations. At the MP4/6-31G*//MP2/6-31G* level, an easy rotation of the NO2 group is predicted for all the radical anions and neutral molecules with the exception of BH2NO2−, BF2NO2−, and BHFNO2−, which show high torsional barriers about the BN bond. Keywords: nitro compounds, radical anions, abinitio calculations, molecular structure.