Fig. 5.
Reaction coordinate diagram for a model reaction. Shown is the reaction coordinate diagram for the model reaction of methanesulfenic acid (2) with imidazole (3), which mimics the reaction of cysteine sulfenic acid with imidazole. A solid line shows a reaction path to the sulfurane derivative (hydroxy-imidazolyl-λ4-sulfanyl)methane (1), and a dotted line shows a possible path for the formation of imidazole-1-sulfenic acid (4) and H2O. For the reaction to the sulfurane derivative, the transition state was found at the B3LYP/6–31G* level of theory.