Complexes of ammonia with propane and cyclopropane: electrostatic guidelines for ab initio treatment

Abstract

A model based on the molecular electrostatic potential (MESP) is employed for the investigation of structures and energies of complexes of ammonia with propane and cyclopropane. The electrostatic model geometries are employed as starting points for an ab initio investigation at the self-consistent field and second-order Moller-Plesset (MP2) levels. The most stable structures of C₃H₆..NH₃ and C₃H₈..NH3 complexes have the interaction energies of 10.07kJ/mol and 8.15kJ/mol, respectively, at the MP2/6-31G(d,p) level. The energy rank order of the structures is not altered with the use of the 6-31++G(d,p) basis set, and the basisset superposition error has little effect. The interaction energy decomposition analysis shows that the electrostatic component is dominant over the other ones. MESP topography thus seems to offer valuable hints for predicting the structures of weakly bonded complexes.