Hydrogen-Bond Dissociation Energies from the Properties of Isolated Monomers.

The strength of binding, as measured by the equilibrium dissociation energy of 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 σ(HX) and σ(B) of the molecular electrostatic surface potentials on the 0.001 e/bohr iso-surfaces of HX and B, respectively, and two recently defined quantities: the reduced electrophilicity Ξ of HX and the reduced nucleophilicity И of B. It is shown that is given by the expression = {σ(HX)σ(B)} И Ξ. This is tested by comparing calculated 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 values in good agreement in general with those calculated ab initio.