ACIDITY OF FIRST-ROW AND SECOND-ROW HYDRIDES - EFFECTS OF ELECTRONEGATIVITY AND HARDNESS

A study is made on the influence of the electronegativity and hardness of a group X on the gas-phase acidities of the first- and second-row hydrides HX. It is shown that these two density functional theory (DFT)-based global properties are sufficient for the correct description of the gas-phase acidity sequences, the group hardness being the more important factor and describing the influence of polarizability effects in the charged forms of the acid-base equilibrium. Various calculated properties of the traditional quantum chemical type (Mulliken charges and the MEP) and DFT-based (local softness), associated with the neutral form of the acid, were found to contain a certain periodicity in their description of the gas-phases acidities. The gas-phase acidities (Delta H-acid and Delta G(acid) values) were also obtained theoretically via quantum statistical thermodynamical calculations at the Hartree-Fock level with the 6-31 + G(*) basis set; these calculated acidities were in fair agreement with the experimental ones. (C) 1995 John Wiley & Sons, Inc.