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Hammett Equation and Generalized Pauling's Electronegativity Equation
Journal of Chemical Information and Computer Sciences, 2004Substituent interaction energy (SIE) was defined as the energy change of the isodesmic reaction X-spacer-Y + H-spacer-H --> X-spacer-H + H-spacer-Y. It was found that this SIE followed a simple equation, SIE(X,Y) = -ksigma(X)sigma(Y), where k was a constant dependent on the system and sigma was a certain scale of electronic substituent constant. It was
Lei Liu 0002 +4 more
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Application of Hammett equation to arylazopyrazoles
Proceedings of the Indian Academy of Sciences - Section A, 1976AE#= Pn,Fax where ux is substituent constant. In figure 1 is shown the dependence of the half wave potential of 3, 5-dimethyl-4-substituted arylazopyrazoles with Hammett constant at pH 4.0. Ortho substituted methoxy and ethoxy groups show deviation due to the steric hindrance and field effects.
Wahid U. Malik, R. N. Goyal
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Plurilinear improvement of the Hammett equation
Journal of Physical Organic Chemistry, 1995AbstractThe original Hammett equation, Δ = ρσ, is transformed in a constrained tetralinear relationship where each straight line with variable intercept term correlates one of the following four groups or subsets of dipolar substituents: normal and special substituents (depending on the absence or the presence of a lone electron pair in their atom next
João Carlos R. Reis +2 more
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THE APPLICATION OF THE HAMMETT EQUATION TO CYCLOPHOSPHAZENES
Phosphorus and Sulfur and the Related Elements, 1977Abstract The applicability of the extended Hammett equation to substituted cyclophosphazene pK a values taken from the literature is demonstrated. Steric effects were shown to be absent or constant by correlation with the LDS form of the extended Hammett equation.
Marvin Charton, Barbara I. Charton
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Hammett equation and micellar effects upon deacylation
Journal of the Chemical Society, Perkin Transactions 2, 1994Substituent effects upon second order rate constants of reaction of OH– with phenyl p-substituted benzoates at surfaces of micelles of cetyltrialkylammonium bromide (alkyl = Me, Et, Pr and Bu) and tetradecylquinuclidinium bromide fit the Hammett equation. Values of ρ increase with increasing bulk of the surfactant head group and are considerably larger
BARTOLETTI A. +4 more
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Extension of the Hammett and Taft Equations
1981Hammett and Taft-type equations can be written for the ionization of many types of acids and bases. Tables A.2 and A.3 list some of the published examples. It has been found empirically (Jaffe, 1953) that as a working approximation the hetero group (— O —, — S —, — NH —) in an unsaturated 5-membered ring carrying an acidic or basic group can be ...
D. D. Perrin +2 more
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Use of the Hammett equation in substituted thiophenes
J. Chem. Soc., Perkin Trans. 2, 1985The application of multivariate statistics to linear free-energy relationships in the thiophene series increases the understanding of the Hammett equation. Principal components analysis shows that α-substituted thiophenes require the σ constants used for para-substituted benzene derivatives, owing to a strict proportionality of the substituent effects ...
ALUNNI, S +6 more
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Limitation of the hepler theory of the Hammett equation
Journal of the Chemical Society, Perkin Transactions 2, 1979Deeper analysis of the assumptions of the Hepler theory leads to the conclusion that for most cases the entropy contributions to the substituent effect cannot be neglected. Hence a limitation of the Hepler theory is apparent.
Tadeusz M. Krygowski +2 more
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