Pattern of Intrinsic Reaction Coordinates and Separatrices for a Symmetry-Forbidden Reaction

The relative distribution of the basins of attraction of the chemical species and of the transi­ tion states is derived for the thermal isomerization of cyclobutene to butadiene. It is shown that the transition states for the symmetry-allowed and symmetry-forbidden path­ ways are lumomers of one another. Use is made of the structural stability principle of Ariel Fernandez and Oktay Sinanoglu to show that these transition states are respectively the conrotatory and disrotatory Jahn-Teller distortions of the 2-butene diradical. The results exhibit good agreement with J. A. Berson’s conclusions in the sense that even the forbidden pathway is concerted. K ey w o rd s : Directed graph of intrinsic reaction coordinates and separatrices, Jahn-Teller distortion of a diradical as a separatrix, symmetry-forbidden reaction pathway.