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In this dissertation the photochemistry of sulfoxides, sulfilimines, and S,C-sulfonium ylides was explored both computationally and experimentally. Dibenzothiophene-S-oxide has been previously shown to undergo deoxygenation to form dibenzothiophene and a reactive intermediate believed to be O(3P). In this study, the photochemistry of S,Csulfonium ylides of thiophenes was explored and shown to result in unimolecular bond scission of the S-C ylidic bond to give the corresponding sulfide and a reactive intermediate, analogous to the chemistry of dibenzothiophene-S-oxide. Chemical trapping studies provide indirect evidence that the reactive intermediate produced upon photolysis is a carbene. The mechanism of unimolecular bond cleavage for sulfoxides was further explored computationally by generating the potential energy surfaces (PES) of thiophene-S-oxide and selenophene-Se-oxide as a function of S-O and Se-O bond length using the CASSCF [18,14] method. Energy corrections were obtained with a second-order perturbation theory (MRMP2). The results for thiophene-S-oxide and selenophene-Se-oxide indicate that the second triplet excited state of each provide nearly barrierless route toward S-O and Se-O bond dissociation. The potential energy diagrams offer a new explanation for the experimentally observed unimolecular bond cleavage of DBTO and DBSeO, in which intersystem crossing from an excited singlet state to a dissociative T2 state provides a pathway to deoxygenation products. This mechanism is consistent with the increased quantum yields of deoxygenation that were experimentally observed for heavy-atom substituted sulfoxides. The bond dissociation enthalpies (BDEs) of several sulfoxides, sulfilimines, S,Csulfonium ylides, and selenoxides were also estimated by applying MP2/6311++G(3df,2p)//MP2/6-31G(d,p), G3, and other computational methods. Selenoxides

Palladium(II) and platinum(II) synthetic peptidases: residue- and sequence-selective hydrolysis and the photochemistry of sulfoxides, S,C-sulfonium ylides, and sulfilimines: unimolecular bond cleavage