| Abstract
| - The oxidation of thianthrene 5-oxide, i.e., a mechanistic probe for the assessment of the electroniccharacter of various oxidants, with peroxybenzoic acids in various oxygen bases as solvents wasinvestigated. The nucleophilicity (XSO) of peroxy acids was increasing with increasing basicity ofthe oxygen base. A good linear correlation was observed by plotting XSO values vs either the Kamlet−Taft β values or the OOH 1H NMR chemical shifts of m-chloroperoxybenzoic acid (m-CPBA) insolvents of various basicity. These observations, together with the results of IR and 1H NMRspectroscopic studies of peroxybenzoic acids, and DFT (B3LYP/6-311++G**) studies of theintramolecular hydrogen bonding in peroxyformic, peroxyacetic, and m-CPBA, as well as theintermolecular hydrogen bonding in the complexes of the these peroxy acids with dimethyl etheras a model oxygen base, support the involvement of the peroxy acid−oxygen base complexes in thetransition states of these reactions. The increased nucleophilicity (XSO) of peroxy acids in basicsolvents is most likely due to the increased negative charge on the terminal “electrophilic”peroxycarboxylic oxygen atom (OH), and/or the increased LUMO and HOMO energies of the peroxyacid in the complexes, as compared to those parameters in the intramolecularly hydrogen-bondedform of peroxy acids, believed to be operative in inert solvents.
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