Rate constants have been determined for hydrogen atom reactions with six sulfhydryl compounds which have structures related to known radiation protectors and sensitizers. A competition technique was utilized to evaluate contributions from the two mechanisms: (a)${\rm H}+{\rm RSH}\overset k_{4}\to{\rightarrow}{\rm H}_{2}+{\rm RS}$, and b)${\rm H}+{\rm RSH}\overset k_{5}\to{\rightarrow}{\rm H}_{2}{\rm S}+{\rm R}$. The rate constant for reaction 4 is influenced by the presence of functional groups within the molecule. It is also found that reaction 4 is the predominant mechanism for hydrogen atom reaction with primary sulfhydryl compounds while reaction 5 is most important for secondary and tertiary SH groups. The relationship of these results to observed radiation protection and sensitizing properties of sulfhydryl compounds is discussed.

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