Relative partition coefficients between aqueous methanol and pentane of the two stereoisomers of a series of 4-tert-butylcyclohexylamines were measured by NMR. The cis isomer shows a larger partition coefficient, with a Delta Delta G(org-->aq)degrees up to 1.4 kcal/mol. A thermodynamic cycle relates these values to a solvent dependence of the A value for conformational equilibrium of an amino substituent. The variation with stereoisomer is attributed to a greater hydrophilicity of a cyclohexylamine with an equatorial amino group, or equivalently to a greater steric bulk of an amino group whose lone pair is hydrogen bonded to water. The strong dependence on solvent inferred for A(NMe2) was confirmed by direct measurement of conformer populations at low temperature.