INTRAMOLECULAR INTERACTIONS BETWEEN SULFUR-ATOMS IN CYCLOTETRATHIOETHER RADICAL CATIONS

Radical cations generated by low temperature steady-state and pulse ra diolysis from 1,4,8,11-tetrathiacyclotetradecane (1) and derivatives b earing gem-dimethyl pairs at the 6- or at the 6- and 13-positions (2 a nd 3, respectively) are characterized by optical absorption spectrosco py. 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 cha racteristic absorptions for 2(.+) and 3(.+) indicates that geometries of radical cations differ substantially from geometries of neutral mol ecules. 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 ge ometries for radical cations involving multiple sulfur interactions we re calculated.