Conformational equilibria in cis-decahydroisoquinoline and C-methyl derivatives: studies using 13C and 1H magnetic resonance spectroscopy

Abstract

¹³ C N.m.r. spectroscopy at 215 K has demonstrated that the conformational equilibrium in cis-decahydroisoquinoline favours the type 1 conformation (70%ΔG° 0.37 kcal mol^–1) in which the nitrogen lone pair is able to occupy the ‘inside’ position. The type 1 and type 2 conformations become degenerate for both cis-decahydroquinoline and cis-decahydroisoquinoline when the nitrogen atom is protonated. The two isomers of cis(4aH,8aH)-3-methyldecahydroisoquinoline are conformationally homogeneous with the 3-methyl substituent equatorial.