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Dynamic NMR study of rotational isomerism in the carbanion of p ‐trifluoromethanesulfonylbenzyltriflone in aprotic solvents
Author(s) -
Gromova Marina,
Béguin Claude G.,
Goumont Régis,
Faucher Nicolas,
Tordeux Marc,
Terrier François
Publication year - 2000
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/1097-458x(200008)38:8<655::aid-mrc706>3.0.co;2-c
Subject(s) - chemistry , carbanion , acetonitrile , solvent effects , acetone , solvent , dimethyl sulfoxide , dilatometer , chemical shift , sulfoxide , carbon 13 nmr , computational chemistry , photochemistry , medicinal chemistry , organic chemistry , thermodynamics , physics , thermal expansion
Rotational isomerism in the conjugate carbanion of p ‐trifluoromethanesulfonylbenzyltriflone was studied by dynamic NMR spectroscopy ( 1 H, 13 C). Treatment of the experimental spectra affords the activation parameters of the processes. The activation enthalpies (∼48 kJ mol −1 ) for the rotational barrier around the C Ar —C α carbon– carbon bond are indicative of a relatively weak π‐order of this bond and are nearly identical in the three dipolar aprotic solvents studied, namely acetonitrile, dimethyl sulfoxide and acetone. Changes in the rates of the conformation exchange around the C Ar —C α bond are mainly a reflection of the solvent dependence of the entropy change (from almost 0 in acetonitrile, to −8 in DMSO and −13 J K −1 mol −1 in acetone). These data are discussed in relation to information on the electronic density distribution, as obtained from an analysis of the 13 C chemical shift of the anion of the benzyltriflone. Copyright © 2000 John Wiley & Sons, Ltd.