X-ray diffraction structural analysis of N-phenylpiperidine having two isopropyl groups in the ortho (1) and a nitro group in the meta (2) positions, has allowed the confirmation of the findings from molecular mechanics calculations on the simple derivative N-(2,6-diisopropylphenyl)piperidine (1) not bearing the nitro group, that the amino function is heavily twisted about the ipso-CN bond. In addition, there are a number of surprising features like the quasi-planarity of the location of the nitrogen atom and the three carbons attached to it, and the flattened nature of the isopropyl group. The hydrochloride (3) of 1 exhibits a peculiar stoichiometry: a hydronium ion coordinates three chloride ions; two of them also establish polar interactions with two NH groups. A great flattening about the N atoms is observed even in this case. The picrate (4) of 1 has the structure of an ammonium salt. Observed CN bond lengths both for the amino and nitro groups, which are to be found in planar and twisted arrangements, raise basic questions about the accepted and simplified views and correlations of substituent-ring interactions.
