Conformational Study by ESR. of Some Alkyl Substituted 6a-Thiathiophthene Radical Anions

ESR. data are reported for the radical anions (II^? to VI^?) of five alkyl substituted 6a-thiathiophthenes. Rates and activation parameters for the inversion of the 3,4-trimethylene chain in IV^?, V^? and VI^? have been obtained by means of an iterative least squares computer program ESRCEX. Preferential conformations of the alkyl substituents are discussed in terms of the 〈cos²θ〉 dependence of the β-proton coupling constants and with the aid of molecular models. Experimental evidence strongly suggests that the partial rotation of the ethyl and isopropyl groups in V^? and VI^? is correlated with the inversion of the 3,4-trimethylene chain.