Some Electronic Correlation Effects in the Topological Analysis of the Laplacian of the Electronic Charge Density in C-n-butonium Cations

LOBAYAN, R.; SOSA, G. L.; JUBERT, A. H.; NELIDA MARIA PERUCHENA

JOURNAL OF PHYSICAL CHEMISTRY A

American Chemical Society Publ

Año: 2005 vol. 109 p. 181 - 190

1089-5639

In this work we present a topological study of the Laplacian of the electronic density using a 6-311++G** basis set, at Hartree-Fock and second order Møller-Plesset (full-electron and frozen core) levels of theory, for the carbocations 2-C-n-Butonium generated upon the insertion of a proton into the secondary C-C bond during the protonation of n-butane. The charge concentration, CC, critical points of the Laplacian distribution at each valence shell, VS, of carbon atoms and the charge concentration closer to hydrogen atoms are studied. Also the bonding critical points of the electronic density are analyzed. We analyze some effects that Coulomb correlation has on topological features of the electronic distribution. It is shown that they are mainly reflected in a decreasing of the charge concentrations at the VS and in a contraction of the VS to the nuclei. They are more pronounced over C-C bonds than in C-H ones. The sensibility of some parameters derived of this topological analysis to the correlation effect of core electrons and of subtle effects related to hyperconjugative interactions are shown. Some consequences of different schemes -double and triple split- valence  basis set  with diffuse and polarization functions- in the definition of subtle VS charge concentrations at 3c-2e bond paths are presented. It is also demonstrated here how the facts that allows us to understand the stability order found in the carbocationic species: 2-C-n-butonium > 1-C-n-butonium > 2-H-n-butonium > 1-H-n-butonium are similarly depicted at correlated and uncorrelated levels of calculation. Keywords: Laplacian, Charge density, carbocations, electronic delocatization, three center-two electrons bond, electronic correlation effects, Coulomb correlation, delocalization indices.