Radical anions of substituted thienothiophens

The e.s.r. spectra of the radical anions of carbonyl-, nitro-, and cyano-derivatives of thieno[3,2-b]thiophen and thieno[2,3-b]thiophen have been investigated in order to compare their properties with those of the corresponding substituted thiophens. From an examination of the hyperfine splitting constants it is concluded that in the case of thieno[3,2-b]thiophen the unpaired electron is delocalized over the whole molecule, while in thieno[2,3-b]thiophen the condensed thieno-group is scarcely involved. Nitrogen coupling constants for (II) and (III), as well as the proton splittings in the mixed terms of ketones (I) indicate that thieno[3,2-b]thiophen has a delocalization power greater than the thieno[2,3-b]thiophen which in its turn is slightly more efficient than thiophen.