Carbon13 chemical shift assignments are reported for Z- and E-doxepin hydrochloride [Z- and E-N,N,-dimethyl-dibenz[b,e]oxepin-delta-11(6H)], gamma-propylamine hydrochloride, and related model compounds. Doxepin hydrochloride, a mixture of approximately 85% E- and 15% Z-isomer is of clinical importance as an antidepressant drug. Previous proton NMR studies indicated that the dibenz(b,e,)oxepin ring exists in two conformations. This study indicates that one conformation may be favored for each isomer with alkylamino olefinic substituent orientation above the most adjacent aromatic ring. Homo- and heteronuclear shift-correlated 2D NMR, selective INEPT, selective and off-resonance decoupling, and inversion-recovery (T1) experiments as well as model compound comparisons were used in assignments.
Dorothy K. Wyatt, Nina M. Roscher, and Lee T. Grady, "Carbon13 NMR of Z- and E-Doxepin Hydrochloride," Appl. Spectrosc. 40, 538-542 (1986)