Hybridization effects on the intrinsic basicities of phosphorus and nitrogen containing bases

Abstract

This paper discuss the influence of hybridization changes at the basic center on the intrinsic basicities of nitrogen and phosphorus containing bases by use of the topological analysis of their charge distributions. The proton affinities of the species investigated, namely HCN, H 2CNH. H 3CNH 2, HCP. H 2CPH and H 3CPH 2 were obtained in the framework of the G2 theory. We have found that within both series of compounds there is a good linear relationship between intrinsic basicities and charge densities at the basic center lone pair. This relationship can be easily rationalized by means of the hybridization model. We have also found that hybridization effects on intrinsic basicities although qualitatively similar for nitrogen and phosphorus are quantitatively larger for the latter. When the hybridization of the basic center changes without changing its coordination, a linear relationship between intrinsic basicities and lone pair charge densities can only be expected if the protonation process does not imply significant structural changes of the base.