Chemometric Analysis of Substituent Effects. II. Relation Between Hammett Substituent Constants σm and σp and a New Model for Quantitative Description of Substituent Effects

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Title:Chemometric Analysis of Substituent Effects. II. Relation Between Hammett Substituent Constants σm and σp and a New Model for Quantitative Description of Substituent Effects
Creators:
Pytela, Oldřich
Journal or Publication Title:
Collection of Czechoslovak Chemical Communications, 59, 2, pp. 381-390

Abstract

<p>The paper presents values of 25 substituent constants σ<sup>i</sup> obtained by optimizing 46 data series of dissociation constants of substituted benzoic acids in various media. The constants σ<sup>i</sup> fulfil the general relation between the substituent constants of the Hammett type in <i>meta</i> and <i>para</i> positions enabling the description of substituent effects from both positions at the same time by a single constant. The Hammett substituent constants are interpreted by means of the σ<sup>i</sup> constants with an accuracy better than 0.03 units. In addition to it, the validity of general relationship between σ<sub>p</sub> and σ<sub>m</sub> was verified on a set of 56 substituents with the prediction accuracy of 0.06 units for σ<sub>p</sub>, and after excluding the probably incorrectly parametrized substituents NHCOC<sub>6</sub>H<sub>5</sub>, CH<sub>3</sub>S, and F the accuracy has improved to 0.05 units (98% of interpreted variability). The given relationship has served as a basis for suggesting a new model of transfer of substituent effects to a reaction centre: the model involves both the Hammett equation and the Yukawa-Tsuno equation and explains their background. The suggested model uses generalized transmission coefficients to separately describe the transformation of a single primary substituent effect - depending on its structure - into one inductive and two resonance effects which are transmitted through two independent channels to the reaction centre and here transformed into the resulting observable effect. From the model it follows that the substituent constant σ<sub>p</sub> is not a substituent constant in the true sense of the word since it involves the characteristics of skeleton and of reaction centre.

Title:Chemometric Analysis of Substituent Effects. II. Relation Between Hammett Substituent Constants σm and σp and a New Model for Quantitative Description of Substituent Effects
Creators:
Pytela, Oldřich
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:59
Number:2
Page Range:pp. 381-390
ISSN:0010-0765
E-ISSN:1212-6950
Publisher:Institute of Organic Chemistry and Biochemistry
Related URLs:
URLURL Type
http://dx.doi.org/10.1135/cccc19940381UNSPECIFIED
ID Code:454
Item Type:Article
Deposited On:06 Feb 2009 17:01
Last Modified:06 Feb 2009 16:01

Citation

Pytela, Oldřich (1994) Chemometric Analysis of Substituent Effects. II. Relation Between Hammett Substituent Constants σm and σp and a New Model for Quantitative Description of Substituent Effects. Collection of Czechoslovak Chemical Communications, 59 (2). pp. 381-390. ISSN 0010-0765

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