Sulfenium radical

Such a unified correlation strongly indicates that the reduction of HRP compound I by thioanisoles proceeds via electron transfer rather than direct oxygen transfer. Electron transfer from the sulfide to HRP compound I in the protein cage might be followed by two competitive processes (i) oxygen rebound to afford the sulfoxide and (ii) diffusion of a sulfenium radical from the protein cage to enable the observation of HRP compound II as shown in Scheme 6 [108]. 

This approach to the thiophene ring seems most direct and involves (1) intramolecular nucleophilic addition of thiol, thiolate, and dithiocarboxylate sulfurs and, in a rare case, sulfide sulfur to sp and sp carbons (2) electrophilic attack of sulfenium and sulfonium ions and their equivalents on unsaturated carbon-carbon bonds (3) addition of thiyl radicals to unsaturated carbon-carbon bonds (4) addition of vinyl and aryl radicals to the sulfur atom of sulfides and (5) electrophilic attack of a carbocation on the sulfur atom of sulfides. 

The second is a complex of sulfenium cation and superoxide and explains the near equivalence of the spin density on the two peroxyl oxygens in thiyl peroxyls. Both valence structures display an exposed electron-deficient sulfur that makes it susceptible to nucleophilic solvents. Complexing with a lone pair donor is expected to stabilize the charge-separated state increasing its contribution to the ground state. A partial radical-cationic character of the sulfur could also make three-electron bonding with some solvents contribute to the charge separation. 

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