Configurational assignments in some dihydrobenzo[c]thiophenes by NMR solvent effects. Correlation of the relative chemical shifts of α-methyl groups with sulphoxide stereochemistry

The configuration of isomeric 3,3-dimethyl-1-phenyl-1,3-dihydrobenzo[c]thiophene 2-oxides was assigned on the basis of selective benzene- and TFA-induced NMR shifts. The same method was employed for assigning the α-methyl resonances of these sulphoxides. Examination of NMR data for a variety of cyclic sulphoxides revealed that in CCl₄ or CDCl₃ solution, α-hydrogen cis to S? O often resonates at higher magnetic field, while α-methyl group cis to S? O characteristically resonates at lower field, than the same hydrogen or methyl group trans to S? O, respectively.