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

Abstract

Abstract1H NMR measurements indicate that (X‐pyridyl)alkanols of the general formula (C5H4N)(CH2)nOH, where n = 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)‐2,2,4,4‐tetramethylpentan‐3‐ols (X = 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 2‐phenylpropan‐2‐ol, only more weakly. Rotation barriers for 3‐(X‐pyridyl)‐2,2,4,4‐tetramethylpentan‐3‐ols (X = 2, 3 or 4) in DMSO or nitrobenzene are 20–21 kcal mol−1. Copyright © 2006 John Wiley & Sons, Ltd.