Electrostatic potential at nuclei as a reactivity index in hydrogen bond formation. Complexes of ammonia with C–H, N–H and O–H proton donor molecules

Abstract

In this study the use of molecular electrostatic potential at atomic sites as a reactivity descriptor for the process of hydrogen bonding is evaluated for a series of complexes involving different types of proton donor molecules and ammonia as a model proton acceptor. The compounds studied were: C 2H 4, CH 3CCH, CH 2CH–CCH, HCN, CH 3NH 2, (CH 3) 2NH, HNC, C 6H 5NH 2, cytosine, HCONHCH3, CH 3OH, C 2H 5OH, C 3H 7OH, C 6H 5OH, HCOOH and H 3CCOOH. Geometry optimisation and vibrational frequency calculations at the optimised geometry were performed for isolated monomers and hydrogen-bonded systems. Density functional theory computations at the B3LYP/6-31G(d,p) were employed. Linear dependence between the molecular electrostatic potential at the hydrogen atom in the isolated monomers and the energy of hydrogen bond formation is found. The results show that the electrostatic potential at atomic sites can be used as a reactivity descriptor for the ability different types of proton donor molecules to form hydrogen bonds.