Redox and EPR spectral behaviour of radical cations of dibenzothiophene and some of its derivatives

The radical cations of dibenzothiophene 1 and its 2,8-[H-2(2)]-isotopomer (2), a series of methylated dibenzothiophenes, viz. 2,8- (3), 3,7- (4) and 4,6-dimethyldibenzothiophene (5), and 2,4,6,8-tetramethyldibenzothiophene (6), as well as 2,2'-(7) and 4,4'-bidibenzothiophene (8) have been generated in 1,1,1,3,3,3-hexafluoropropan-2-ol, mostly by Tl-III trifluoroacetate or 4-tolyl-Tl-III trifluoroacetate oxidation. From the hyperfine coupling constants obtained, it is concluded that the 2- and 4-positions of 1(.+) are the carbon atoms possessing the highest spin density. This assignment agrees with results of high-level quantum-chemical calculations, placing the B-2(1) state as the lowest energy level of 1(.+).