lntramolecularly formed S : . N three-electron-bonded radical cations have been identified as transient intermediates in the 'OH radical-induced oxidation of 3-(methylthio)propylamine, methionine, and methionine ethyl ester. A similarly bonded radical is also indicated in the reduction of dehydromethionine by hydrated electrons. Intramolecular S : . 0-bonded intermediates are suggested to be formed in the'OHinduced oxidation of 4-(methylthio) butyric acid and S-methylcysteine. All these three-electron-bonded species exhibit optical absorptions with maxima in the 380-400 nm range. The observable S:.Obonded transient from S-methylcysteine is presumed to be protonated at oxygen. Favourable steric structures, particularly five-membered rings, significantly increase the probability of formation and the overall stability of a particular three-electron bond. Under comparable conditions, i.e. structure, substituents, consecutive chemistry, etc., the S : .
Acknowledgment. We thank the National Science Foundation (CHE-8510067) for support of this work and Donna Van Engen for a helpful discussion.Registry No. 1, 2, hexamethylbenzene, Supplementary Material Available: Bond lengths and bond angles, with standard deviations, for 2 (Tables IV and V), final anisotropic thermal parameters for chlorine (Table VI), and atomic parameters for hydrogen (Table VII) (3 pages). [The structure factor table is available from the author.] Ordering information is given on any current masthead page.
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