. Can. J. Chem. 53,167(1975).The influence of substituents on the conformational properties of N-substituted 5,6-dihydro-7H,12H-dibenz[c,fjazocines and their conjugate acids was studied by n.m.r. spectroscopy. The position of the equilibrium between a rigid boat-chair and a flexible twist-boat conformation has been measured. The twist-boat conformation in deuterochloroform increased as the size of the substituent increased. However, the effect was opposite for the series of conjugate acids in trifluoroacetic acid.A number of inversion barriers for the boat-chair twist-boat and the twist-boat* twistboat equilibria in CDCI3 and TFA were determined. It was found that all barriers to interconversion were raised on protonation. The barrier to racemization for the twist-boat form of the quaternary methiodide of 1 was found to be > 18 kcal/mol. Chem. 53,167(1975).On a CtudiC, par spectroscopie r.m.n., I'influence des substituants sur les proprittbs conformationnelles de dihydro-5,6 7H,12H-dibenz[cflazocines N-substitubs e t de leurs acides conjugues. On a mesure la position de l'dquilibre entre une conformation rigide bateau-chaise e t une conformation flexible bateau-croise. La conformation bateau-croisb dans le chloroforme deutbre augmente mesure que la grosseurdu substituant augmente. Toutefois I'effet est oppost pour la serie des acides conjugues dans I'acide trifluoroacCtique. On a determine, dans CDCI3 et dans TFA, un certain nombre de barrieres d'inversion pour les dquilibres bateau-chaise vs. bateau-croise et bateau-croise vs. bateau-croise. On a trouve que toutes les barrieres aux interconversions sont augmentees par protonation. La baniere a la racemisation, dans la forme bateau-croisd du sel d'ammonium quaternaire de 1, est plus grande que 18 kcal/mol.[Traduit par le journal]We have recently described a study of the conformational properties of N-methyl-5,6-dihydro-7H,12H-dibenz[c,f lazocine, 1, by means of proton n.m.r. spectroscopy (1). This compound is of inherent interest as an unexplored medium sized heterocycle, as well as serving as a model for 1,4-cyclooctadiene, for which no experimental evidence has been r e p~r t e d .~ The 'NRCC No. 14326. 'NRCC Postdoctoral Fellow 1972. 'In a recent paper Dunitz and Waser (2a) proposed two conformers, the rigid and flexible forms, for 1,4-cyclooctadiene. Subsequently Turner et al. (2b) suggested the rigi4 form as being energetically favored. This nomenclature, as pointed out to us by one of the referees, is based upon dynamic rather than static characteristics of each conformer. In spite of our use of the terms "rigid crown" and "flexible" conformers in our previous azocine was found to possess two stable conformations, the boat-chair (BC) and twist-boat (TB) forms, whose barrier for the TB -+ BC transformation amounted to 15.3 kcal/mol (1). We wish to report an extension of these studies to include azocines 2-6 in which the bulk of substituents at the nitrogen atom varies considerably. In this manner, the influence of the substituent on the conformational pr...