DFT study of pericyclic and pseudopericyclic thermal cheletropic decarbonylations. Evaluation of magnetic properties.

A comprehensive B3LYP/6-31G** study of various thermal cheletropic decarbonylations was conducted. The complete pathway for each reaction was determined, and changes in magnetic susceptibility and its anisotropy were monitored with a view to estimating the aromatization associated to each process. This information, together with the energy and structural results, allowed us to clarify cases that are not clearly pseudopericyclic or pericyclic from previous work. Also, our results reveal that pericyclic reactions involve no disconnection in the cyclic array of overlapping orbitals. Therefore, a pseudopericyclic reaction involves at least one such disconnection. In any case, pseudopericyclic reactions involving two disconnections exhibit much clearer features, which facilitates their classification.