Conformational studies of 5-acetyl-10-cyano-10,11-dihydro-5H-dibenz[b,f]azepine

5 - Acetyl - 10 - cyano - 10,11 - dihydro - 5H - dibenz[b,f]azepine, 3, has been synthesized and its conformations in solution have been studied by variable temperature NMR. At ?55° in CDCl₃ solution, 3 shows the signals due to four different conformational isomers. At 55°, signals due to only two conformers can be seen. The ABX pattern of each of the four conformers was analyzed using double resonance experiments and the LAOCN3 computer program. The relative abundances of the isomers in the mixtures were estimated by computer additions of different proportions of the spectra calculated for the separate isomers. These spectral observations are discussed in detail and interpreted in terms of slow inversion of the seven-membered ring by torsion of the 4a55a bonds and restricted twisting of the C10C11 ethylene bridge.