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.