Proton NMR and IR study of self‐association in pyridylalkanols: open or cyclic dimers? higher polymers?

Abstract

1 H NMR measurements indicate that (X-pyridyl)alkanols of the general formula (C 5 H 4 N)(CH 2 ) n OH, where n ¼ 1, 2 or 3, self-associate as open dimers, cyclic dimers, trimers and tetramers, with considerable variations depending on the position of the alkyl chain and its length. 2-(X-Pyridyl)propan-2-ols behave like the corresponding pyridylmethanols with, however, somewhat lower association constants. The IR spectra of 3-(X-pyridyl)-2,2,4,4tetramethylpentan-3-ols (X ¼ 3 or 4) in carbon tetrachloride suggest weak association, while the 2-pyridyl derivative occurs mainly as the intramolecularly hydrogen-bonded rotamer. The OH NMR shifts for the 3-and 4-pyridyl derivatives in benzene are concentration-dependent, but neither the equilibrium constants nor the degree of association can be evaluated. Benzyl alcohol in benzene associates as an open dimer and a cyclic tetramer, as does 2phenylpropan-2-ol, only more weakly. Rotation barriers for 3-(X-pyridyl)-2,2,4,4-tetramethylpentan-3-ols (X ¼ 2, 3 or 4) in DMSO or nitrobenzene are 20-21 kcal mol À1 .

Interplay of thermochemistry and Structural Chemistry, the journal (volume 21, 2010) and the discipline

“…The solution phase complexation enthalpy of Cu(II) with the latter two alcohols has been directly determined [73]; we know of no such measurement for the first species. The sole enthalpy measurement we know of for this species is that involving its intra-and intermolecular hydrogen bonding, a study that involves the other two pyridine alcohols as well [74].…”