Analysis of the Ortho Effect: Basicity of 2-Substituted Benzonitriles

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Title:Analysis of the Ortho Effect: Basicity of 2-Substituted Benzonitriles
Creators:
Exner, Otto
Böhm, Stanislav
Journal or Publication Title:
Collection of Czechoslovak Chemical Communications, 71, 8, pp. 1239-1255
Uncontrolled Keywords:<i>Ab initio</i> calculations, Conformation analysis, Isodesmic reactions, Steric effects, Benzenes, Nitriles, Basicity, Hydrogen bonds, Substituent effects

Abstract

Energies of 18 <i>ortho</i>-substituted benzonitriles and their protonated forms were calculated within the framework of the density functional theory at the level B3LYP/6-311+G(d,p). The substituent effects were evaluated in terms of isodesmic reactions as the effects on the basicity on the one hand and separately in the nitrile molecules and in the cations on the other. The ortho effect was defined as the difference when compared to the 4-substituted isomers. It is smaller than in the case of <i>ortho</i>-substituted benzoic acids but not negligible (up to 25 kJ mol<sup>-1</sup>). In unprotonated molecules it may be classified as purely steric effect, in spite of the small dimension of the CN group and estimates made with the calotte models. In the protonated forms, polar properties of the substituent are decisive. In addition, a new, quite important substituent effect was discovered with the substituents OH, SH, CHO and COOCH<sub>3</sub>, which is controlled by different conformation of protonated and unprotonated molecules. Substituents OH, SH and NH<sub>2</sub> form also weak hydrogen bonds in unprotonated nitriles. In summary, 2-substituted benzonitriles allowed evaluating of several, partly new substituent effects but cannot serve as model molecules without an ortho effect, although the constant functional group CN is sterically little pretentious. <p>

Title:Analysis of the Ortho Effect: Basicity of 2-Substituted Benzonitriles
Creators:
Exner, Otto
Böhm, Stanislav
Uncontrolled Keywords:<i>Ab initio</i> calculations, Conformation analysis, Isodesmic reactions, Steric effects, Benzenes, Nitriles, Basicity, Hydrogen bonds, 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:71
Number:8
Page Range:pp. 1239-1255
ISSN:0010-0765
E-ISSN:1212-6950
Publisher:Institute of Organic Chemistry and Biochemistry
Related URLs:
URLURL Type
http://dx.doi.org/10.1135/cccc20061239UNSPECIFIED
ID Code:2538
Item Type:Article
Deposited On:06 Feb 2009 17:19
Last Modified:06 Feb 2009 16:19

Citation

Exner, Otto; Böhm, Stanislav (2006) Analysis of the Ortho Effect: Basicity of 2-Substituted Benzonitriles. Collection of Czechoslovak Chemical Communications, 71 (8). pp. 1239-1255. ISSN 0010-0765

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