Steric Effects and Steric Inhibition of Resonance in Isopropylbenzoic Acids in the Gas Phase and in Solution

[img]PDF - Authorized users only
Language: English
141Kb
Title:Steric Effects and Steric Inhibition of Resonance in Isopropylbenzoic Acids in the Gas Phase and in Solution
Creators:
Fiedler, Pavel
Kulhánek, Jiří
Decouzon, Michèle
Gal, Jean-François
Maria, Pierre-Charles
Exner, Otto
Journal or Publication Title:
Collection of Czechoslovak Chemical Communications, 64, 9, pp. 1433-1447
Uncontrolled Keywords:Conformation analysis, Inhibition of resonance, Induced dipole, Acidity, IR spectroscopy, Steric effects, Benzoic acids, Substituent effects

Abstract

The substituent effects of the isopropyl group in 2-, 3- and 4-isopropylbenzoic acids were investigated on the enthalpies of formation, gas-phase acidities, acidities in methanol and in dimethyl sulfoxide, and on the IR spectra in tetrachloromethane. Particular attention was given to the influence of variable conformation on the observed steric effect. In contrast to 2-<i>tert</i>-butylbenzoic acid and similarly to 2-methylbenzoic acid, 2-isopropylbenzoic acid exists in two planar conformations in equilibrium. Due to this conformational freedom, the steric effects of the isopropyl group on the conformation of the carboxyl group or on the gas-phase acidity are relatively small, rather close to that of a methyl group. The gas-phase acidity can be qualitatively described in terms of pole/induced dipole interaction in the anion. The latter effect is observable with a lower intensity even in 3-isopropylbenzoic acid: in this action from a more remote position, the isopropyl group resembles more the <i>tert</i>-butyl than the methyl group. In methanol and dimethyl sulfoxide solutions, the steric effects and particularly the pole/induced dipole interaction are attenuated and effect of isopropyl acquires intermediate values between methyl and <i>tert</i>-butyl. Solvent effects are thus deciding for the position of the isopropyl substituent on the scale of steric substituent constants. <p>

Title:Steric Effects and Steric Inhibition of Resonance in Isopropylbenzoic Acids in the Gas Phase and in Solution
Creators:
Fiedler, Pavel
Kulhánek, Jiří
Decouzon, Michèle
Gal, Jean-François
Maria, Pierre-Charles
Exner, Otto
Uncontrolled Keywords:Conformation analysis, Inhibition of resonance, Induced dipole, Acidity, IR spectroscopy, Steric effects, Benzoic acids, 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:64
Number:9
Page Range:pp. 1433-1447
ISSN:0010-0765
E-ISSN:1212-6950
Publisher:Institute of Organic Chemistry and Biochemistry
Related URLs:
URLURL Type
http://dx.doi.org/10.1135/cccc19991433UNSPECIFIED
ID Code:1568
Item Type:Article
Deposited On:06 Feb 2009 17:10
Last Modified:06 Feb 2009 16:10

Citation

Fiedler, Pavel; Kulhánek, Jiří; Decouzon, Michèle; Gal, Jean-François; Maria, Pierre-Charles; Exner, Otto (1999) Steric Effects and Steric Inhibition of Resonance in Isopropylbenzoic Acids in the Gas Phase and in Solution. Collection of Czechoslovak Chemical Communications, 64 (9). pp. 1433-1447. ISSN 0010-0765

Repository Staff Only: item control page