Conformation of Aromatic Carbonyl Derivatives: An Infrared Study

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Title:Conformation of Aromatic Carbonyl Derivatives: An Infrared Study
Creators:
Fiedler, Pavel
Exner, Otto
Journal or Publication Title:
Collection of Czechoslovak Chemical Communications, 69, 4, pp. 797-810
Uncontrolled Keywords:Conformation, Methyl benzoates, Inhibition of resonance, IR spectroscopy, Steric effects, Chemometrics, Acetophenones, Ketones, Substituent effects

Abstract

Infrared spectra of 14 methyl- and polymethyl-substituted acetophenones and of 14 equally substituted methyl benzoates were investigated in the carbonyl region in tetrachloromethane solution and correlated with their conformation. The ν(C=O) frequency depends moderately on the inductive effect of substituents and more sensitively on the steric effect of ortho substituents. Steric effects are not simply related to the torsion angle ϕ (calculated by the density functional theory) but are better described by dividing the methyl substituents into three classes: nonplanar derivatives with methyl groups in the two ortho positions, slightly nonplanar derivatives with two methyl groups in the positions 2 and 3 (buttressing effect), and the remaining derivatives existing in two equilibrium planar conformations. Eleven various physical properties of methyl-substituted acetophenones, measured or calculated previously, were now correlated by principal component analysis (PCA). Two components are necessary to explain 93% of variance; they relate roughly to the steric and inductive effects. Steric effect affects all properties while inductive effect is of importance mainly for the gas-phase basicities and wavelengths in the UV spectra. Both can be separated very effectively using the classic comparison of ortho and para derivatives; in this way, the steric effect is isolated and in a subsequent PCA only one component is sufficient to explain 94% of variance. <p>

Title:Conformation of Aromatic Carbonyl Derivatives: An Infrared Study
Creators:
Fiedler, Pavel
Exner, Otto
Uncontrolled Keywords:Conformation, Methyl benzoates, Inhibition of resonance, IR spectroscopy, Steric effects, Chemometrics, Acetophenones, Ketones, Substituent effects
Divisions:Life and Chemical Sciences > Institute of Organic Chemistry and Biochemistry > Collection of Czechoslovak Chemical Communications
Journal or Publication Title:Collection of Czechoslovak Chemical Communications
Volume:69
Number:4
Page Range:pp. 797-810
ISSN:0010-0765
E-ISSN:1212-6950
Publisher:Institute of Organic Chemistry and Biochemistry
Related URLs:
URLURL Type
http://dx.doi.org/10.1135/cccc20040797UNSPECIFIED
ID Code:2243
Item Type:Article
Deposited On:06 Feb 2009 17:16
Last Modified:06 Feb 2009 16:16

Citation

Fiedler, Pavel; Exner, Otto (2004) Conformation of Aromatic Carbonyl Derivatives: An Infrared Study. Collection of Czechoslovak Chemical Communications, 69 (4). pp. 797-810. ISSN 0010-0765

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