¹³C NMR spectra of benzo[b]thiophene and 1‐(X‐benzo[b]thienyl)ethyl acetate derivatives

Carbon‐13 chemical shift assignments are reported for benzo[ b ]thiophene and 1‐(X‐benzo[ b ]thienyl)ethyl acetate derivatives, where X=CH(OAc)CH 3 substituted at positions 2‐7. Substituent chemical shift (SCS) effects for the ethyl acetate group are additive at all positions. A substantial upfield shift was observed at C‐3, arising from the peri interaction of H‐3 and the 4‐ethyl acetate substituent. Carbon‐13 relaxation times ( T 1 ) and nuclear Overhauser enhancements (η) have been measured for benzo[ b ]thiophene and its derivatives, and the contributions of dipolar, T DD 1 , and spin rotation, T SR 1 , relaxation have been determined. Intramolecular dipole–dipole interactions are found to provide by far the most important spin‐lattice relaxation mechanism whenever protons are bound directly to the carbons under investigation. Nonprotonated ring carbons are relaxed by both DD and SR mechanisms. Anisotropic motion has an easily observable effect on the DD contribution to T 1 , and can form the basis for spectral assignments, as in 1‐phenylethyl acetate. Long‐range 13 C 1 H coupling constants were observed both between ring carbons and between ring carbons with ring side‐chain hydrogens. These results have been used for the structure determination of the title compounds.