Results 121 to 130 of about 1,354 (166)

Plurilinear improvement of the Hammett equation

Journal of Physical Organic Chemistry, 1995
AbstractThe 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, Manuel A. P. Segurado, Jaime D. Gomes De Oliveira   +2 more
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THE APPLICATION OF THE HAMMETT EQUATION TO CYCLOPHOSPHAZENES

Phosphorus and Sulfur and the Related Elements, 1977
Abstract 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, 1994
Substituent 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., BARTOLINI S., GERMANI, Raimondo, SAVELLI, Gianfranco, BUNTON C. A.   +4 more
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Extension of the Hammett and Taft Equations

1981
Hammett 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, Boyd Dempsey, E. P. Serjeant   +2 more
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Use of the Hammett equation in substituted thiophenes

J. Chem. Soc., Perkin Trans. 2, 1985
The 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, CLEMENTI, S, EBERT, C, LINDA, P, MUSUMARRA, Giuseppe, SJOSTROM, M, WOLD, S.   +6 more
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Limitation of the hepler theory of the Hammett equation

Journal of the Chemical Society, Perkin Transactions 2, 1979
Deeper 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, Jean Guilleme, Bruno Wojtkowiak   +2 more
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Multiparameter Extensions of the Hammett Equation

1978
The Hammett equation (1937)2,3,4 takes forms (4.1), (4.2), where k or K is the rate or equilibrium constant for a side-chain reaction of a meta- or $$\log k^0 = \log k^0 + \rho \sigma $$ (4.1) $$\log K^0 = \log K^0 + \rho \sigma $$ (4.2) para-substituted benzene derivative.
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Applications of the Hammett Equation to Heterocyclic Compounds

1976
Publisher Summary This chapter describes the applicability of Hammett-type parameters that may be tested for heterocyclic compounds in a number of different ways. Work on specific heterocyclic systems may be grouped under two headings: The ring heteroatom as a substituent and reactivity of heteroatoms, as affected by other substituents.
P. Tomasik, C.D. Johnson
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Applications of the Hammett Equation to Heterocyclic Compounds

1964
Publisher Summary The Hammett equation is one of the most widely applied relations between the structure and reactivity of organic compounds. This equation relates the relative reactivities of the series of di- and poly-substituted benzene derivatives.
H.H. Jaffe, H. Lloyd Jones
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Further Applications of Hammett and Taft Equations

1981
The success of the method of prediction based on the additivity of increments of pK a values along chains in a molecule is not evidence of the correctness of the assumption that inductive effects are of overriding importance. Ring formation, by constraining the substituent in much closer proximity to the acidic or basic centre, leads to a stronger ...
D. D. Perrin, Boyd Dempsey, E. P. Serjeant   +2 more
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