Conformational equilibria in N-alkyl-cis-decahydroquinolines

Analyses of low temperature 1H, 13C, and 19F n.m.r.spectra show that replacement of the nitrogen-attached hydrogen in cis-decahydroquinoline by the alkyl groups methyl, ethyl, and βββ-trifluoroethyl leads to a shift in the conformational equilibrium from a preference for type 2 conformation to preference for type 1. The activation energy Ea for the interconversion 1 → 2 of 1-(βββ-trifluoroethyl)-cis-decahydroquinoline was determined as 68 kJ mol–1 by a full line-shape analysis of the 19F spectra recorded between 245 and 312 K.