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NMR study on trapping techniques to deduce the conformations of 1-alkyl-3- hydroxypiperidines

✍ Scribed by J. J. Van Luppen; J. A. Lepoivre; R. A. Dommisse; F. C. Alderweireldt

Publisher
John Wiley and Sons
Year
1982
Tongue
English
Weight
573 KB
Volume
18
Category
Article
ISSN
0749-1581

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✦ Synopsis

Abstract

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.

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