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## Abstract 2,2,4,4‐Tetramethyl‐3‐{2‐[3,4‐dialkoxy‐5‐(3‐pyridyl)]thienyl}pentan‐3‐ols self‐associate both in the solid state and in solution. The IR spectra of the solids display a broad OH absorption at 3320 cm^−1^, corresponding to an intermolecularly hydrogen‐bonded __syn__ rotamer, probably a dimer, as well as absorptions around 3500 cm^−1^ of the intramolecularly hydrogen‐bonded __anti__ form. Well‐crystallized samples of these derivatives go into solution in the __syn__ form but undergo rotation to the __anti__ rotamer at a rate which can be measured directly by proton Nuclear Magnetic Resonance (NMR) spectroscopy. The diethoxy derivative was studied in a wide variety of solvents. The activation energy for __syn__→__anti__ rotation is practically solvent‐independent, whereas that of the reverse reaction falls in hydrogen‐bonding solvents, by more than 2 kcal mol^−1^ on going from chloroform or benzene to dimethylsulfoxide (DMSO). By combining direct measurements at low temperature and Dynamic Nuclear Magnetic Resonance (DNMR) results at high temperature, rotation rates were evaluated over a range of more than 100 K, and significantly large negative activation entropies determ

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Author

John S. Lomas

Publisher

John Wiley and Sons; Wiley (John Wiley & Sons); John Wiley & Sons Inc.; Wiley (ISSN 0894-3230)

Published

2007

Language

EN

Field

Chemistry (Physical Sciences)