monnat, vogel, and sordo, in 2002, measured the kinetics of addition of sulfur dioxide to 1,2-dimethylidenecycloalkanes. they wrote that the reaction of 1,2-dimethylidenecyclohexane with sulfur dioxide can give two different products depending on reaction conditions. the reaction makes the corresponding sultine through a hetero-diels-alder reaction under kinetic control (≤ -60 °c), but, under thermodynamic control (≥ -40 °c), the reaction makes the corresponding sulfolene through a cheletropic reaction. the activation enthalpy for the hetero-diels-alder reaction is about 2 kcal/mol smaller than that for the corresponding cheletropic reaction. the sulfolene is about 10 kcal/mol more stable than the isometric sultine in ch2cl2/so2 solution.