Internal bond rotation in substituted methyl radicals, H2B-CH2, H3C-CH2, H2N--CH2, and HO-CH2: Hardness profiles

The energy profiles for the internal bond rotation of substituted methyl ra dicals, X-CH2 (X = BH2, CH3, NH2, and OH) were examined with B3LYP/6-31G(d) calculations. Energy evaluation of each point along the rotational coordin ate was also carried out with single-point calculation at the computational levels of B3LYP/6-311+G(2df,p) and QCISD(T)/6-311+G(2df,p). The computed r otational energy profiles, as well as the calculated values for the geometr ical parameters, the vibrational frequencies, and the ionization potential, were in reasonable agreement with previously reported experimental and the oretical results. Except for H3C-CH2 radical, the profiles of chemical pote ntial and hardness along the rotational coordinates present striking contra st to those expected from the corollary of the principle of maximum hardnes s. Thus, there seems to be no rigorous reason for hardness to be minimum in the transition state region, in general.