RESUMEN
Photolysis of aromatic sulfoxides in the presence of alkoxides in alcoholic solvents provides a photochemical route to the corresponding sulfides. Other electron donors also give sulfide with various degrees of success. The reaction could also be carried out using carbazoles as sensitizers, and quantitative yields could be obtained using N-methylcarbazole in methanol. Evidence points toward a hydroxysulfuranyl radical as the key intermediate, and solvent effects point to heterolysis, rather than homolysis, as the step that breaks the S-O bond.
RESUMEN
Gas-phase activation data were obtained for model sulfoxide elimination reactions. The activation enthalpy for methyl 3-phenylpropyl sulfoxide is 32.9 +/- 0.9 kcal/mol. Elimination by methyl vinyl sulfoxide to form acetylene has an enthalpic barrier of 41.6 +/- 0.8 kcal/mol and that of 3-phenylpropyl methanesulfinate to form hydrocinnamaldehyde is 34.6 +/- 0.6 kcal/mol. Calculations at the MP2/6-311+G(3df,2p)//MP2/6-31G(d,p) level for simplified models of these reactions provide barriers of 32.3, 40.3, and 32.7 kcal/mol, respectively. A series of other compounds are examined computationally, and it is shown that the substituent effects on the sulfoxide elimination reaction are much more straightforward to interpret if DeltaH data are available in addition to the usually determined DeltaH++. The activation enthalpy of the reverse addition reaction is also subject to structural variation and can usually be rationalized on the basis of nucleophilicity of the sulfur or polarity matching between the sulfenic acid and olefin derivative.
RESUMEN
The effect of a methanesulfinyl group on the photophysics of several aromatic chromophores is reported. The spectroscopic singlet and triplet energies are affected only modestly, compared to that parent arenes, but the fluorescence yields fall by at least 1 order of magnitude. Fluorescence lifetimes are short. Fluorescence enhancements are observed on cooling the sulfoxides from room temperature to 77 K. High quantum yields of stereomutation are reduced as the temperature drops. There is not a consistent effect on triplet or phosphorescence yields. It is proposed that these results are consistent with a nonradiative pathway for deactivation of the singlet that results in stereomutation. A modest activation energy of a few kcal/mol is estimated for the photochemical racemization of 1-methanesulfinylpyrene.