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NMR study on trapping techniques to deduce the conformations of 1‐alkyl‐3‐ hydroxypiperidines
Author(s) -
Van Luppen J. J.,
Lepoivre J. A.,
Dommisse R. A.,
Alderweireldt F. C.
Publication year - 1982
Publication title -
organic magnetic resonance
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0030-4921
DOI - 10.1002/mrc.1270180406
Subject(s) - chemistry , alkyl , aqueous solution , protonation , isopropyl , nuclear magnetic resonance spectroscopy , solvent , heptane , proton nmr , trapping , crystallography , nmr spectra database , stereochemistry , spectral line , medicinal chemistry , organic chemistry , ion , ecology , physics , astronomy , biology
The conformational equilibrium of 1‐alkyl‐3‐hydroxypiperidines in n ‐heptane and aqueous solution is investigated. Several methods, e.g. IR and NMR spectroscopy, are discussed. The conformation trapping in D 2 SO 4 ‐D 2 O mixtures, and subsequent analysis of the 1 H and 13 C NMR spectra, is proven to be the most reliable method. In an apolar solvent the conformation with an axial hydroxyl group is always dominant (69%). In aqueous solution the same conformation predominates in the protonated form (56%, pH<5), while only 43% of this conformation is present in the free base (pH∼11). A detailed 13 C NMR study is described of 1‐isopropyl‐3‐hydroxypiperidine in aqueous solution at pH between 2 and 11.