Hardness and Chemical Potential Profiles for Some Open-Shell HAB → HBA Type Reactions. Ab Initio and Density Functional Study

The electronic structure, hardness (η), and chemical potential (μ) for the 1A‘ and 3A‘‘ states of HNO−HON and the 2A‘‘ state of HSO−HOS have been calculated using HF/6-311++G** and B3LYP/6-311++G** methods. The η and μ profiles of the 1A‘ state of HNO−HON and those of HSO−HOS are obtained in agreement with the salient features of the maximum hardness principle (MHP). However, a quite erratic η profile is predicted for the 3A‘‘ state of HNO−HON. This can be attributed to the nature of the variation in the energy difference of the two states along the reaction path. The relative energies, ionization potentials (I), and electron affinities (A) are calculated at the stationary points of the B3LYP surface using B3LYP and MPn (Full) methods. Most of these values are obtained in very good agreement with the available experimental data. The η values based on these I and A identify the most stable species correctly but do not follow the expected trend with regard to the relative stability of the transition state. The reason for this anomaly is discussed.