Hydrogen bond energetics from topological analysis of experimental electron densities: Recognising the importance of the promolecule

In a recent paper [E. Espinosa, E. Molins, C. Lecomte, Chem. Phys. Lett. 285 (1998) 170] the kinetic energy density G(r(c)) and potential energy density V(r(c)) at the bond critical point r(c) in X-H ... O hydrogen bonds were deduced from topological analyses of experimental electron distributions extracted from accurate X-ray diffraction experiments. We show that the promolecule, a model of non-interacting overlapping spherical atomic electron densities, can explain many of the observed results as well as the exponential dependence on the H ... O distance. This raises the question of whether present experimental results differ from a simple reference model for weak interactions. (C) 1999 Elsevier Science B.V. All rights reserved.