The interaction of sulphur atoms with ethylene

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Abstract
A correlation diagram shows that 1D sulphur atoms may add to ethylene in a least-motion symmetry-allowed process. The computed potential surface for the interaction of a sulphur atom with an ethylene molecule reveals another local minimum in addition to the one leading to thiirane. This second minimum leads to the insertion product, vinyl thiol. We examine the potential surface in some detail to decide if both reactions branch from the same transition state or whether they are competing concerted processes. The latter view is favoured. Similar potential surfaces are calculated for a S(3P) configuration. A minimum leading to addition is found, but the one leading to insertion is lacking. The stereospecific addition of S(3P) is attributed to a correlation with an excited state of thiirane which retains CC bonding. A ring-opened thiirane intermediate is computed, with a planar geometry and a CSC angle of 114°. It closes by a conrotatory route with a calculated activation energy of 24 kcal/mole. We find no ground state intermediate in which a CS bond is broken. In the excited configuration of a thiirane we find two minima—one for a planar geometry with the CC bond cleaved, the other for a species with a CS bond broken, but retaining the original configuration of the CH2CH2 part.