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Aromatic solvent effect on the rotational isomerism in 2‐hydroxy‐5‐methyl‐3‐nitroacetophenone
Author(s) -
Konopacka Aleksandra,
Pawełka Zbigniew
Publication year - 2005
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.988
Subject(s) - chemistry , conformational isomerism , solvent , solvent effects , dielectric , dipole , polar , alkyl , computational chemistry , benzene , acetonitrile , relative permittivity , molecule , permittivity , organic chemistry , physics , optoelectronics , astronomy
The internal rotation of the hydroxyl group in 2‐hydroxy‐5‐methyl‐3‐nitroacetophenone ( I ) is associated with the transformation of the OH· · ·O 2 N bond (weakly polar Ib conformer) into the OH· · ·OC bond (strongly polar Ib conformer). The standard Gibbs energy, Δ G °, for the Ia ⇌ Ib conformational equilibrium was estimated in benzene and its 10 alkyl derivatives using dipole moment measurements and infrared spectroscopy. The parent Onsager–Böttcher model for the continuum–homogeneous dielectric medium completely fails to predict the dependence of Δ G ° on the relative permittivity, ε, of the solvent. The size of the solvent molecules seems to be the important factor qualifying the conformer–solvent interaction. The continuum–heterogeneous model of two concentric dielectric continua with local and bulk relative permittivities and the mean spherical approximation (MSA) approach allow consideration of this factor in the series of the aromatic solvents investigated. In addition to these two models, a satisfactory description of the solvents' influence is achieved in terms of the correlation of Δ G ° with the dipolarity/polarizabilty parameter π* of the solvents. Copyright © 2005 John Wiley & Sons, Ltd.