Intramolecular interactions between sulfur atoms in cyclotetrathioether radical cations

Abstract

Radical cations generated by low temperature steady-state and pulse radiolysis from 1,4,8,11-tetrathiocyclotetradecane (1) and derivatives bearing gem-dimethyl pairs at the 6- or at the 6- and 13-positions (2 and 3, respectively) are characterized by optical absorption spectroscopy. Despite very different conformations for the neutral compounds 1–3 their radical cations (1˙⁺–3˙⁺) possess similarly located σ→σ* transitions (about 450 nm) for structures characterized by the strongest interactions between sulfur atoms. Delayed formation of characteristic absorptions for 2˙⁺ and 3˙⁺ indicates that geometries of radical cations differ substantially from geometries of neutral molecules. In the case of 3˙⁺ an intermediate structure (λ_max= 600 nm) was intercepted which rearranged to the most stable structure (λ_max= 450 nm) both thermally or photochemically. Optimized geometries for radical cations involving multiple sulfur interactions were calculated.