Three center-two electron and four center-four electron bonds. A study by electron Charge density over the structure of methonium cations.

OKULIK, N. B.; NELIDA MARIA PERUCHENA; JUBERT, A. H.

JOURNAL OF PHYSICAL CHEMISTRY A

American Chemical Society

Lugar: American Chemical Society; Año: 2006 vol. 110 p. 9974 - 9982

1089-5639

We study  the electronic density charge topology of CH5+ species, 1 (Cs), 2 (Cs), and 3 (C2v) at ab initio level using the Theory of Atoms in Molecules (AIM) developed by Bader. In spite of the reports of previous studies concerning carbocationic species, the methane molecule is protonated at the carbon atom, which clearly shows its pentacoordination. In addition to the fact that hydrogen atoms in the methonium molecule behave in a very fluxional fashion and that the energy difference among the species 1, 2 and 3 are very low, is important to point out that two different topological situations can be defined on the basis of our study of the topology of the electronic charge density.  Then, the species 1 and 2 present a 3c-2e bond of singular characteristics as compared with other carbocationic species but in the species 3 the absence of a 3c-2e bond is noteworthy. This structure can be characterized through the three bond critical points (BCP) found, corresponding to saddle points on the path bonds between the C-H(2,3,5) that lie in the same plane. These nuclei define a four centers interaction where the electronic delocalization produced among the s (C-H) bonds provide a stabilization of the three C-H bonds involved in this interaction (the remaining two C-H bonds are similar to those belonging to the non protonated species). Our results show that bonding situations with a higher number of atom arrays are possible in protonated hydrocarbons.