Results 151 to 160 of about 10,545 (194)

Theoretical considerations concerning the hammett equation — VIII

Tetrahedron, 1963
Abstract The resonance contribution, PR, to Hammett p values, and the Taft-Lewis parameter α have been calculated for five aromatic oxygen acids. The method of calculation consisted of a crude calculation by the LCAO MO method of the changes of charge distribution in an acid molecule effected by a substituent, and an assessment of the effect of this ...
J.L. Roberts, H.H. Jaffé
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Application of the Hammett Equation to Fused Ring Systems

Journal of the American Chemical Society, 1954
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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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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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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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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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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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The Hammett Equation—the Present Position

1972
This chapter represents—in a certain sense—the introduction to the whole book, since the Hammett equation is the oldest and most developed empirical relationship, and many general features can be demonstrated by using it as the only available example. For this reason this chapter will deal with the Hammett equation in a broad sense and many statements ...
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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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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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