The crystal structures of a pair of diastereomeric salts of (-)-(2R, 3R)-O, O′-di-p-toloyl tartaric acid and (-)- and (+)-3-N,N-dimethylamino-1,1-diphenyl-1-butanol have been determined. Crystal data: 3: (-)-(R)-C₁₈H₂₄NO⁺, (-)-(2R, 3R)-C₂₀H₁₇O^-₈, orthorhombic, P2₁2₁2₁, a = 7.873(2), b = 15.343(3), c = 28.76(1) Å, V = 3474(2) ų, Z = 4, and D_cale = 1.254 g cm^-3. 4: (+)-(S)-C₁₈H₂₄NO⁺, (-)-(2R, 3R)-C₂₀H₁₇O^-₈, orthorhombic, P2₁2₁2₁, a = 7.504(1), b = 17.215(2), c = 26.490(4) Å, V = 3422.0(8) ų, Z = 4, and D_calc = 1.273 g cm^-3. The geometries and the conformational energies of the solid state conformations of the cations have been compared with global and local energy minimum conformations determined by molecular mechanics calculations. In the solid state, one conformation with and one without an intramolecular hydrogen bond are observed. The calculated global energy minimum conformation in aqueous solution contains the intramolecular hydrogen bond.