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Unexpected shielding of methyl group protons in some piperidines
Author(s) -
Manimekalai A.,
Maruthavanan T.,
Selvaraju K.
Publication year - 2008
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.2177
Subject(s) - chemistry , group (periodic table) , chemical shift , proton nmr , methyl group , ethyl ester , medicinal chemistry , stereochemistry , crystallography , organic chemistry
High resolution 1 H and 13 C NMR spectra of four 3‐ethyl‐4‐hydroxy‐ 4‐phenylpiperidines 1–4 have been recorded in CDCl 3 and analysed. The conformations of phenyl and hydroxyl groups at C(4) and ethyl group at C(3) were analysed in detail. The chemical shift of the methyl protons in the ethyl group are quite surprising; they are close to TMS in CDCl 3 and even negative in DMSO– d 6 . These results are interpreted in terms of the magnetic anisotropy of the phenyl rings at C(2) and C(4) which, in turn, depend on the conformations of the ethyl group at C(3) and the hydroxyl group at C(4). Favoured conformations of ethyl group at C(3) and hydroxyl group at C(4) were calculated by AM1 methods. Copyright © 2008 John Wiley & Sons, Ltd.