Journal of the American Chemical Society p. 3057 - 3062 (1987)
Update date:2022-08-02
Topics:
Wagner, Peter J.
Lindstrom, Michael J.
The photochemistry of β-,γ-and δ-phenacyl sulfides, sulfoxides, and sulfones has been studied.The first group undergoes no irreversible reaction.The other two undergo type II photoelimination but in low quantum efficiency.Analysis of triplet lifetimes and product quantum yields indicates that all undergo rapid internal quenching, which is ascribed to a charge-transfer (CT) process.The positional dependence of rate constants for this CT reaction is β > γ > α >> δ > ε .Some rate constants (units of 1E8 s-1) for PhCO(CH2)nSBu are as follows: n = 1, 16; n = 2, 55; n = 3, 29; n = 4 ,1.7; n = 5, = 0.2.These values are interpreted as representing relative equilibrum constants for achieving cyclic orientations in which the sulfur lone pair and the half-empty oxygen n-orbital overlap substantially.The rate constants are very sensitive to the oxidation state of sulfur; for the n = 3 sulfoxide, k = 35 * 1E8; for the n =3 sulfoxide k = 0.35 * 1E8.The δ-substituted ketones undergo elimination to form 4-benzoyl-1-butene, by β-elimination of sulfur-centered radicals from the biradicals that intervene in the type II elimination.Actual radical cleveage rate constants lie in the order SCN > PhS <*> BuS(O) >> BuS, BuSO2, CH3CO-S and range from 1E9-3*1E5 s-1.Rate constants for triplet state γ-hydrogen abstraction were found to correlate well with the ?1 values of the various sulfur groups, except for δ-sulfinyl, which apparently participates in the reaction.
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