Correspondence between the one-electron potential and the Laplacian of the electron density as indicators of proton affinity

Proton affinities for a series of alkyl amines and phosphines formed from successive alkylation of NH3 and PH3 are known to exhibit linear correlation with (3,3) critical points of N and P in the distribution of the Laplacian of the electron density, ∇2ρ. We show that these proton affinities also exhibit linear correlation with valence minima of N and P in the distribution of the one-electron potential (OEP), ∇2ρ(r)/2ρ(r). These results provide evidence of the correspondence between OEP and ∇2ρ as quantitative indicators of proton affinity.