Substituent effects in heterocyclic rings. An electron spin resonance study of some 5-substituted 2-thienyl nitroxides and nitro-anions

E.s.r. spectra of some 5-substituted 2-thienyl nitroxides, generated by scavenging triethylsilyl radicals with substituted nitrothiophens, and nitro-anions have been recorded in order to determine the effective substituent delocalising power with respect to an unpaired electron in the thiophen series. The results are discussed in connection with chemical data. Hyperfine splitting constants calculated for the substituted nitro-anions by the INDO method, using an s,p basis set for the sulphur atom, are in good agreement with the experimental values.