The extraordinary richness of the reaction between diazomethane and tetracyanoethylene: can computational calculations shed light on old papers?

Abstract

In the quest of the structure of the intermediate between Δ¹- and Δ²-pyrazolines, the reactivity of these molecules tetrasubstituted by cyano groups in adjacent positions (3,3,4,4 or 4,4,5,5) has been explored in their neutral and protonated forms. Many reactions reported in the literature for pyrazolines have been studied and quantified (energies and transition states). Thirty-three structures of pyrazolines, their open-ring counterparts and their complexes are described. Acid–base equilibria, rotations, electrocyclic reactions and sigmatropic transpositions are reported.