Pericyclic versus pseudopericyclic reactions.: What the Laplacian of the charge density, del2ρ(r), has to say about it?: The case of cycloaddition reactions

The pseudopericyclic character of a group of cycloaddition reactions is theoretically investigated with the quantum theory of atoms in molecules of Bader at B3LYP/6-311++G(d,p) and MP2/6-311++G(d,p) levels of theory. The analysis of the topology of the Laplacian of the charge density, del(2)rho(r), along the reaction coordinate sets out a clear cut between pericyclic and pseudopericyclic processes and also allows one to account for intermediate cases.