1,5-Dithiacyclooctane is shown to chemically react more efficiently and to remove singlet oxygen from solution more rapidly than either thiane or 1,4-dithiane. These unusual characteristics of the 1,5-dithiacyclooctane reaction were explored using ab initio quantum chemical methods. A large number of persulfoxides, thiadioxiranes, and hydroperoxy sulfonium ylides were located and their structures analyzed. The unusual efficiency of the reaction was attributed to a conformational change that electrostatically stabilized the persulfoxide and increased the potential energy barrier for physical quenching.