Conformation of syn- and anti-3-substituted cis-hexahydrocarbazoles from nuclear magnetic resonance coupling constants

Abstract

Double-irradiation experiments have been used to interpret the n.m.r. spectra of the methiodides of syn- and anti-3-substituted N-methyl-cis-hexahydrocarbazoles. The Karplus relation and conformational theory have been used qualitatively to rationalise the characteristic splitting patterns and coupling involving the ring junction protons, thus distinguishing between alternative conformations.For the syn-series and the 3,3-dimethyl compound it is suggested that the alicyclic ring adopts a rigid shallow boat conformation. The anti-compounds are probably conformationally mobile at probe temperature.