A theoretical approach to substituent effects. Interactions between directly bonded groups in the neutrals X?NH2, X?OH,and X?F and the anions X?NH− and X?O−

Ab initio molecular orbital calculations have been carried out for the neutrals X? NH₂, X? OH, and X? F and the anions X? NH^? and X? O^? with substituents X = Li, BeH, BH₂, CH₃, NH₂, OH, and F. All structures have been fully optimized with the 4-31G basis set which is found to perform considerably better than the minimal STO-3G basis in predicting the lengths of strongly polar bonds. A quantitative analysis of interactions between the directly bonded groups, utilizing energy changes in hydrogenation reactions, is presented and rationalized with the aid of perturbation molecular orbital theory. Favorable interactions occur when electron-donor groups bond to electron-acceptor groups. This applies to both σ and π interactions, the relative importance of which depends on the particular substituents.