Experimental electron density overlapping in hydrogen bonds: topology vs. energetics

We have investigated the relationship between the energetic properties of the hydrogen bond (HB) interaction and the topological overlapping of the electronic clouds at the H...O critical point r(CP). This study involves a total of 83 X-H...O (X = C, N, O) HBs, which have been described in terms of the topological properties of the electron density rho(r) at r(CP) for a large set of compounds. Kinetic G(r(CP)) and potential V(r(CP)) contributions to the local energy density of electrons exhibit linear functionalities against, respectively, the positive and negative curvatures of rho(r) at the critical point, showing an effective deconvolution in the local form of the Virial theorem. The topological variation of the curvatures at r(CP), and therefore changes in the H...O overlapping, are related to the onset of the repulsion between the electronic clouds of the basic and acid atoms. (C) 1999 Elsevier Science B.V. All rights reserved.