Chemometrical Analysis of Substituent Effects. XIII. Comparison of Substituent Effects on Dissociation and Chemical Shift in 13C NMR Spectra of Mono- and Disubstituted Benzoic Acids

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Title:Chemometrical Analysis of Substituent Effects. XIII. Comparison of Substituent Effects on Dissociation and Chemical Shift in 13C NMR Spectra of Mono- and Disubstituted Benzoic Acids
Creators:
Kulhánek, Jiří
Pytela, Oldřich
Lyčka, Antonín
Journal or Publication Title:
Collection of Czechoslovak Chemical Communications, 65, 1, pp. 106-116
Uncontrolled Keywords:Dissociation of benzoic acids, <i>ortho</i> Effect, Disubstitution, <sup>13</sup>C substituent-induced chemical shifts

Abstract

The <sup>13</sup>C chemical shifts have been measured of the carboxyl carbon atoms for all the 2-, 3-, and 4-substituted benzoic acids with H, CH<sub>3</sub>, CH<sub>3</sub>O, F, Cl, Br, I, and NO<sub>2</sub> substituents, as well as for all 3,4-, 3,5-, and 2,6-disubstituted benzoic acids with combinations of CH<sub>3</sub>, CH<sub>3</sub>O, Cl (or Br), NO<sub>2</sub> substituents and for symmetrically 2,6-disubstituted derivatives with Et, EtO, PrO, <i>i</i>-PrO, and BuO substituents. The chemical shifts of carboxylic group carbon atoms of the 3- and 4-substituted derivatives show correlation only with the substituent constants σ<sub>I</sub>. For the 2-substituted derivatives was found the dependence only on σ<sub>I</sub> and on the υ constant describing steric effects (<i>s</i> = 0.122, <i>R</i> = 0.996, without the CH<sub>3</sub> derivative which has a distinct anisotropic effect). The substituent effects on the carboxylic carbon chemical shift show additivity with 3,4-, 3,5-, and 2,6-substituents, and the 2,6-disubstituted derivatives show a linear synergic effect of substituents due obviously to the steric hindrance to resonance. Application of the principal component analysis to the data matrix involving all the combinations of mono- and disubstitution involving the above-mentioned substituents has proved an identical substituent effect from all the positions on the chemical shift described by one latent variable, steric effects and anisotropic behaviour of methyl at the 2 and 2,6 positions being predominantly described by the second latent variable (with the total explained variability of 99.5%). Comparison of substituent effects on the chemical shift of carboxylic carbon with that on the dissociation constant measured in the same solvent has confirmed the anisotropy due to <i>ortho</i> methyl group, the <i>ortho</i> halogen substituents in monosubstituted derivatives also having a different effect. The dependence of chemical shift on p<i>K</i><sub>a</sub> was not very close for the derivatives studied (<i>s</i> = 1.005, <i>R</i> = 0.690). The inclusion of anisotropy of <i>ortho</i> alkyl group by means of an indicator variable improved the correlation (<i>s</i> = 0.533, <i>R</i> = 0.925), and omitting of 2-F, 2-Cl, 2-Br, and 2-I substituents gave a regression without deviating points (<i>s</i> = 0.352, <i>R</i> = 0.968). <p>

Title:Chemometrical Analysis of Substituent Effects. XIII. Comparison of Substituent Effects on Dissociation and Chemical Shift in 13C NMR Spectra of Mono- and Disubstituted Benzoic Acids
Creators:
Kulhánek, Jiří
Pytela, Oldřich
Lyčka, Antonín
Uncontrolled Keywords:Dissociation of benzoic acids, <i>ortho</i> Effect, Disubstitution, <sup>13</sup>C substituent-induced chemical shifts
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:65
Number:1
Page Range:pp. 106-116
ISSN:0010-0765
E-ISSN:1212-6950
Publisher:Institute of Organic Chemistry and Biochemistry
Related URLs:
URLURL Type
http://dx.doi.org/10.1135/cccc20000106UNSPECIFIED
ID Code:1627
Item Type:Article
Deposited On:06 Feb 2009 17:11
Last Modified:06 Feb 2009 16:11

Citation

Kulhánek, Jiří; Pytela, Oldřich; Lyčka, Antonín (2000) Chemometrical Analysis of Substituent Effects. XIII. Comparison of Substituent Effects on Dissociation and Chemical Shift in 13C NMR Spectra of Mono- and Disubstituted Benzoic Acids. Collection of Czechoslovak Chemical Communications, 65 (1). pp. 106-116. ISSN 0010-0765

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