Calculated CNO 2 bond dissociation energies

Abstract

The effect of substituents on CNO 2 bond energies was explored with high level calculations. Geometries for the compounds NO 2CXH 2; X = H, F, OH, NH 2, CH 3 and NO 2CHY; Y = O, CH 2 were optimized with the 3-21G basis set. Bond energies, calculated with full MP4/6-31G* energies, were corrected to 298 K by including scaled zero-point corrections and heat capacity corrections. In the series where X was varied, the bond dissociation energy (BDE) remained nearly constant (59.0–62.3 kcal/mol). In contrast, the NO 2CHO bond is much weaker (52.0 kcal/mol) and the NO 2CHCH 2 bond is much stronger (71.0 kcal/mol) compared to the CNO 2 bond in the NO 2CXH 2 series. Bond strengths were compared when H replaces NO 2. It was found that the constant CNO 2 bond energy in the NO 2CXH 2 series is due to two offsetting effects. Namely, substituents which increase the intrinsic bond energy (IBE) also increase the stability of the radical.