Theoretical exploratory study of the strong conformational and diastereotopic effects found in the vertical anion of α-halogen-substituted open-chain and three-membered ring compounds bearing a heteroatom (N, O, P)

Abstract

A theoretical exploratory comparison of steric effects in the ground state and unstable temporary anion species formed by electron attachment has been achieved for open-chain and three-membered ring compounds bearing O, N, and P atoms. The quantum calculations have been carried out at the MP2/6–311G ∗∗ level. When dealing with open-chain compounds, it is found that a very important enhancement of rotation barriers is found in the anion states. This effect mostly arises from through-space interaction of the odd electron which is predominantly located in σ ∗ CH and σ ∗ XH MOs, concentrated around the H atoms, and the O and N-lone pair electrons. The role of F and Cl substituents is analyzed with respect to unsubstituted compounds. The same type of effect is observed in cyclic compounds. No such strong interactions are present in P-substituted compounds. It is thus emphasized that very strong diastereotopic effects would exist in temporary anionic moieties having high negative EAs. in O and N-substituted series.