INTRAMOLECULAR INTERACTIONS BETWEEN SULFUR-ATOMS IN CYCLOTETRATHIOETHER RADICAL CATIONS

Radical cations generated by low temperature steady-state and pulse radiolysis from 1,4,8,11-tetrathiacyclotetradecane (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 sigma-->sigma* 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 (lambda(max) = 600 nm) was intercepted which rearranged to the most stable structure (lambda(max) = 450 nm) both thermally or photochemically. Optimized geometries for radical cations involving multiple sulfur interactions were calculated.