The first conformer-specific partition coefficients are presented. Relationships between the macroscopic and the rotamer-specific partition coefficients are deduced. Constituents of the determination are shown to be the conformer (rotamer) mole fractions in both solvents and the macroscopic partition coefficient. Feasibility of the method is exemplified on amphetamine, a flexible molecule of psychostimulant activity. Partition coefficients of the most hydrophilic and most lipophilic amphetamine rotamers differ by a factor of 1.4. The conformer-specific partition coefficients are interpreted in terms of intramolecular interactions of the moieties, which are modulated by solvation effects on the rotamer-specific group settings.