Hydrogen-Bond Dissociation Energies from the Properties of Isolated Monomers

Abstract

The strength of binding, as measured by the equilibrium dissociation energy Deof an isolated hydrogen-bonded complex B···HX, where B is a simple Lewis base and X = F, Cl, Br, I, CN, CCH, or CP, can be determined from the properties of the infinitely separated components B and HX. The properties in question are the maximum and minimum values σmax(HX) and σmin(B) of the molecular electrostatic surface potentials on the 0.001 e/bohr3iso-surfaces of HX and B, respectively, and two recently defined quantities: the reduced electrophilicity ΞHXof HX and the reduced nucleophilicity ИBof B. It is shown that Deis given by the expression De= {σmax(HX)σmin(B)} ИBΞHX. This is tested by comparing Decalculated ab initio at the CCSD(T)(F12c)/cc-pVDZ-F12 level of theory with that obtained from the equation. A large number of complexes (203) falling into four categories involving different types of hydrogen-bonded complex B···HX are investigated: those in which the hydrogen-bond acceptor atom of B is either oxygen or nitrogen, or carbon or boron. The comparison reveals that the proposed equation leads to Devalues in good agreement in general with those calculated ab initio.