The rhombohedral crystals of (+)-fl-l,2,5-trimethyl-4-phenylpiperidin-4-ol are in space group R~, with a= 29-754, c= 7"713/~, and Z= 18. The structure has been determined by the direct method and has been refined to R = 0.054 for 1410 observed reflexions. The molecular structure is the same as that found for the monoclinic form except for a substantial change in the direction of the O-H bond and small changes in some of the valence angles. The piperidine ring has a skewed chair form, the phenyl ring is axial, and the three methyl groups are equatorial. Each six molecules which are related by the 3 symmetry are linked together by O-H. • • N' bonds into a hexameric ring of alternating (+) and (-) molecules.

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