The Hammett substituent constants and effects of medium

Pytela, Oldřich; Ludwig, Miroslav; Večeřa, M.

doi:10.1135/cccc19862143

Cited by 11 publications

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“…pK = pK 0 -ρ X σ p -ρ Y σ p , Hammett model with substituent constants σ p for both nuclei 2. pK = pK 0 -ρ X σ p -ρ Y σ p -, Hammett model with substituent constants σ p for X substituents and substituent constants 17 σ p -for Y substituents 3. pK = pK 0 -ρ X σ P6 -ρ Y σ P6 , Hammett model with substituent constants σ P6 adjusted from processes in non-aqueous media 18 4. pK = pK 0 -ρ IX σ I -ρ RX σ R -ρ IY σ I -ρ RY σ R , Taft model with separated inductive (I) and mesomeric (R) effects of substituents 17 5. pK = pK 0 -ρ X σ p -ρ Y [σ p + r(σ p --σ p )], additive model presuming X substituents to act according to the Hammett relationship with substituent constant σ p and Y substituent to act according to the Yukawa-Tsuno relationship, where r describes the extent of mesomeric effects 19 .…”

Section: Resultsmentioning

confidence: 99%

Effect of para Substitution on Dissociation of N-Phenylbenzenesulfonamides

Mansfeld

Pařík

Ludwig

2004

Collect. Czech. Chem. Commun.

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The reaction of substituted anilines and benzenesulfonyl chlorides has been used to prepare 49 substituted N-phenylbenzenesulfonamides of general formula 4-X-C 6 H 4 SO 2 NHC 6 H 4 -Y-4′. Their purity was checked by elemental analysis. The substituents X and Y include H, CH 3 , CH 3 O, Cl, Br, CN, and NO 2 . The dissociation constants of all compounds were determined by potentiometric titration in methanol, acetonitrile, N,N-dimethylformamide, and pyridine. The obtained dissociation constants, pK HA , were correlated with various sets of substituent constants. It was found that the effects of substituents X and Y on the dissociation are best described by using the Hammett equation with σ p constants and the Yukawa-Tsuno equation with σ p -and σ p constants, respectively. This result confirms the direct conjugation of Y substituent with the reaction centre. The explained variability using the additive model was above 96% in all the solvents used. The data also provided information about the transmission effect of the SO 2 group. The average dissociation constants were further processed by the latent variables methods, principal components and conjugated deviations analyses.

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Section: Resultsmentioning

confidence: 99%

Effect of para Substitution on Dissociation of N-Phenylbenzenesulfonamides

Mansfeld

Pařík

Ludwig

2004

Collect. Czech. Chem. Commun.

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“…The medium-induced changes in substituent constants are considerable for some substituents [23][24][25] . This is not surprising with polar substituents having localized charges 23 (NO 2 , SO 2 CH 3 , COCH 3 , NHCOCH 3 ) or readily ionized substituents 23 (OH, SH, COOH), but the behaviour of bulky alkyl groups 20,24 (i-Pr, t-Bu) is surprising.…”

Section: Chemometric Analysis Of Substituent Effectsmentioning

confidence: 99%

Chemometric Analysis of Substituent Effects. X. Unification and Reparametrization of Substituent Constants in Hammett-Type Equations by Means of Alternative Interpretation of Substituent Effects (AISE)

Pytela

1996

Collect. Czech. Chem. Commun.

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The paper deals with evaluation of validity of substituent scales σ m , σ p , σ p 0 , σ p + , and σ p − in Hammetttype equations. Possible reasons of unreliability of these scales and conceivable ways of verification of individual substituent constants are discussed. On the basis of Alternative Interpretation of Substituent Effects (AISE) and four additional conditions, a regression nonlinear model has been suggested which includes the dependence of all above-mentioned substituent scales upon a single interpreting variable -the σ i substituent constant. This model has been applied to the 32 most frequent substituents from each scale, i.e. altogether 160 substituent constants taken from literature. The optimization of 17 unknown regression parameters gave the residual standard deviation s = 0.180 and, after excluding 12 remote values, s = 0.061. The analysis of residua proved their standard and statistical appropriateness of the model. The agreement between literature values and predicted values of substituent constants was the best with the σ m scale; on the other hand, the largest differences were encountered with the σ p + scale. The found differences above a current reliability limit of substituent constants were due first to unreliability of some literature data and next to solvent effects and (in some cases) specific properties of substituents.For chemists the substituent effects represent one of the means used in studies of electron density in a chemical system. It is a long time since the first formulation of the Hammett equation 1 which transformed the then more or less qualitative approach into a quantitative tool. Although other approaches have appeared (for reviews see refs 2-8 ) since that time, the Hammett equation still belongs among the most significant correlation relations. In the field of quantitative relations between chemical structure and physico-chemical or biological properties as well as in studies of reaction mechanisms there exist a number of good reasons for preference of a simple correlation model of this sort irrespective of the relatively limited validity range and/or the worse fit of correlation. More complex and more sophisticated correlation equations can provide a greater number of relevant pieces of information which, however, require a greater number of experiments of higher precision.Chemometric Analysis of Substituent Effects

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“…In recent years Pytela and coworkers 120 have obtained indications of a solvent effect on m and/or p for NO 2 . This research group determined the apparent pK a values for a large number of substituted benzoic acids in one-component organic solvents 121 .…”

Section: B Aromatic Systemsmentioning

confidence: 99%

“…As an example of this kind of work, the recent contributions of the group of Ludwig and Pytela will be mentioned briefly. Reference has already been made to the earlier work of these authors in determining the dissociation constants of a large number of substituted benzoic acids in different solvents (Section III.B) 120,121 . The results were treated as a data matrix by the chemometric methods referred to above, and various sets of Hammett values were derived for the 35 substituents involved.…”

Section: B Theoretical Techniquesmentioning

confidence: 99%

Electronic Effects of Nitro, Nitroso, Amino and Related Groups

Shorter¹

2009

Patai's Chemistry of Functional Groups

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The Hammett substituent constants and effects of medium

Cited by 11 publications

References 0 publications

Effect of para Substitution on Dissociation of N-Phenylbenzenesulfonamides

Effect of para Substitution on Dissociation of N-Phenylbenzenesulfonamides

Chemometric Analysis of Substituent Effects. X. Unification and Reparametrization of Substituent Constants in Hammett-Type Equations by Means of Alternative Interpretation of Substituent Effects (AISE)

Electronic Effects of Nitro, Nitroso, Amino and Related Groups

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