Effect of Ring Strain on the Thiolate-Disulfide Exchange. A Computational Study.

B3LYP/aug-cc-pVDZ and MP2/6-31+G[sup *] calculations of the reactions of HS with small cyclic disulfides (dithiirane, 1,2-dithietane, 1,2-dithiolane, and 1,2-dithiane) were performed to determine the reaction mechanismo For the five- and six-membered rings, the reaction proceeds via the addition-elimination pathway, consistent with acyclic analogues. The smaller, more strained threeand four-membered rings react by the S[sub N]2 mechanism. Addition of the nucleophile cannot be accommodated by the small rings without concomitant ring cleavage. [ABSTRACT FROM AUTHOR]