J. Luppen, J. Lepoivre, R. Dommisse
Apr 1, 1982
Citations
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Influential Citations
5
Citations
Journal
Magnetic Resonance in Chemistry
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 D2SO4-D2O mixtures, and subsequent analysis of the 1H and 13C 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 13C NMR study is described of 1-isopropyl-3-hydroxypiperidine in aqueous solution at pH between 2 and 11.