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An NMR investigation of the conformational equilibria of 2‐(2′‐pyridyl)ethylphosphonic acid in several solvents
Author(s) -
Petterson Krag A.,
Fort Diana,
Wei Peter D.,
Roberts John D.
Publication year - 2002
Publication title -
chirality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.43
H-Index - 77
eISSN - 1520-636X
pISSN - 0899-0042
DOI - 10.1002/chir.10064
Subject(s) - chemistry , steric effects , hydrogen bond , vicinal , pyridine , intramolecular force , conjugate acid , dimethyl sulfoxide , solvent , methanol , lone pair , proton nmr , proton , solvent effects , crystallography , medicinal chemistry , stereochemistry , organic chemistry , molecule , ion , physics , quantum mechanics
Vicinal proton–proton NMR couplings have been used to investigate whether the position of conformational equilibria is determined by intramolecular N‐H hydrogen bonding for 2‐(2′‐pyridyl)ethylphosphonic acid 1 in its various possible ionization states in water, methanol, ethanol, and dimethyl sulfoxide (DMSO). With 1 in the form of its monoanion and dianion, the trans is favored, with the dianion being more trans than the monoanion for a given solvent, probably as the result of steric effects, possibly enhanced by repulsive electrostatic effects between the negatively charged phosphonic group and the lone pair on the pyridine nitrogen. For 1 and its conjugate acid, the gauche amounts, respectively, to 43% and 45% in water, 66% and 51% in methanol, 66% and 64% in ethanol, and 29% and 49% in DMSO. For these latter two species, electrostatic, steric, and hydrogen bonding‐effects are all likely to play a role in determining the conformational equilibria. Chirality 14:204–208, 2002. © 2002 Wiley‐Liss, Inc.