Crystal structures of two chiral piperidine derivatives: 1-[(1R)-2-hydroxy-1-phenylethyl]-piperidin-4-one and 8-[(1S)-1-phenylethyl]-1,4-dioxa-8-azaspiro[4.5]decane-7-thione

The crystal structures of the two title piperidine derivatives show different conformations for the six-membered heterocycle. The N-substituted 4-piperidinone 1-[(1R)-2-hydroxy-1-phenylethyl] piperidin-4-one, C13H17NO2, (I), has a chair conformation, while the piperidine substituted in position 2 with a thiocarbonyl group, 8-[(1S)-1-phenylethyl]-1,4-dioxa-8-azaspiro[4.5]-decane-7-thione, C15H19NO2S, (II), features a half-chair conformation. Comparison of the two structures, and data retrieved from the literature, suggests that the conformational flexibility is mainly related to the hybridization state of the C atom alpha to the piperidinic N atom: a Csp(3) atom favours the chair conformer, while a Csp(2) atom distorts the ring towards a half-chair conformer. In the crystal structure of (I), weak C-H center dot center dot center dot O hydrogen bonds link the molecules into supramolecular chains propagating along the b-axis direction. In the crystal of (II), the molecules are linked by weak C-H center dot center dot center dot S contacts into supramolecular chains propagating along the b-axis direction.