Self‐association in {2‐[3,4‐alkylenedioxy‐5‐(3‐pyridyl)]‐thienyl}alkanols: an NMR,IR, and single‐crystal X‐ray study |
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Authors: | John S. Lomas Christine Cordier Alain Adenier François Maurel Jacqueline Vaissermann |
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Affiliation: | 1. Interfaces, Traitements, Organisation et Dynamique des Systèmes, Université de Paris 7, CNRS UMR 7086, 1 rue Guy de la Brosse, 75005 Paris, FranceInterfaces, Traitements, Organisation et Dynamique des Systèmes, Université de Paris 7, 1 rue Guy de la Brosse, 75005 Paris, France.===;2. Interfaces, Traitements, Organisation et Dynamique des Systèmes, Université de Paris 7, CNRS UMR 7086, 1 rue Guy de la Brosse, 75005 Paris, France;3. Laboratoire de Chimie Inorganique et Matériaux Moléculaires, Université de Paris 6, CNRS UMR 7071, Case 42, 4 place Jussieu, 75252 Paris Cedex 05, France |
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Abstract: | syn‐2,2,4,4‐Tetramethyl‐3‐{2‐[3,4‐alkylenedioxy‐5‐(3‐pyridyl)]thienyl}pentan‐3‐ols self‐associate both in the solid state and in solution. Single‐crystal X‐ray diffraction study of the 3,4‐ethylenedioxythiophene (EDOT) derivative shows that it exists as a centrosymmetric head‐to‐tail, syn dimer in the solid state. The IR spectra of the solids display only a broad OH absorption around 3300 cm?1, corresponding to a hydrogen‐bonded species. 1H Nuclear Overhauser Effect Spectroscopy (NOESY) NMR experiments in benzene reveal interactions between the tert‐butyl groups and the H2 and H6 protons of the pyridyl group. Two approaches have been used to determine association constants of the EDOT derivative by NMR titration, based on the concentration dependence of (i) the syn/anti ratio and (ii) the OH proton shift of the syn rotamer. Reasonably concordant results are obtained from 298 to 323 K (3.6 and 3.9 M?1, respectively, at 298 K). Similar values are obtained from the syn OH proton shift variation for the 3,4‐methylenedioxythiophene (MDOT) derivative. Concentration‐dependent variation of the anti OH proton shift in the latter suggests that the anti isomer associates in the form of an open, singly hydrogen‐bonded dimer, with a much smaller association constant than the syn rotamer. Self‐association constants for 3‐pyridyl‐EDOT‐alkanols with smaller substituents vary by a factor of 4 from (i‐Pr)2 up to (CD3)2, while the hetero‐association constants for the same compounds with pyridine vary slightly less. Copyright © 2007 John Wiley & Sons, Ltd. |
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Keywords: | hydrogen bonding rotamers self‐association hetero‐association |
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