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13C n.m.r. spectra of dimethyl l-isopropyldibenzo[ b,e]bicyclo[2.2.2]octatriene-7,8-dicarboxylate disclose the existence of both dl and meso isomers, whereas 'H n.m.r. spectra were interpreted by the sole existence of the former. Characteristic chemical shifts for the rotamers were found, among others, for carbons along the rotational axis. The non-equivalence is most probably attributed to the difference in geometry about the carbons in question. An unusual fact was also that the more compressed methyl carbon of the isopropyl group gives a signal at higher field.