The strength of binding, as measured by the equilibrium
dissociation
energyDeof 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 thatDeis given by the expressionDe= {σmax(HX)σmin(B)} ИBΞHX. This is tested by comparingDecalculated 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 toDevalues in good agreement
in general with those calculated ab initio.