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Conformational equilibria of ephedrine and pseudoephedrine and hydrogen bonding
Author(s) -
Tsai Helen,
Roberts John D.
Publication year - 1992
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.1260300905
Subject(s) - chemistry , vicinal , hydrogen bond , conformational isomerism , deuterium , protonation , ephedrine , hydrogen–deuterium exchange , stereochemistry , crystallography , deuterium nmr , hydrogen , nuclear magnetic resonance spectroscopy , photochemistry , molecule , organic chemistry , physics , quantum mechanics , neuroscience , biology , ion
Proton NMR spectra suggest that the conformation with trans vicinal hydrogens is favored for ephedrine as the free base in deuterium oxide, although in non‐polar solvents, such as deuteriotrichloromethane, the gauche vicinal hydrogen conformations are favored, as has been reported previously. The conjugate acid has primarily gauche hydrogens. In contrast, the trans ‐hydrogen rotamers of pseudoephedrine dominate for both the non‐protonated and protonated forms in deuterium oxide. Hydrogen bonding is unlikely to be as important as usually assumed in determining the conformational preferences of these substances.