Results 111 to 120 of about 17,649 (161)

Replacement Substituent Constants for Simple Heterocycles

Tetrahedron, 1989
Abstract 13 C nmr absorptions are reported for the β-vinylic carbon atoms in 15 series of ethylenes bearing heterocyclic substituents. The data are used to establish the best single-parameter substituent constants, σ 13 , for the various heterocycles as replacements for para -substituted benzenes.
Charles N. Robinson, Leonard J. Wiseman, Carl D. Slater   +2 more
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Substituent effects on the ionization constants of phenylazobenzaldoximes

Canadian Journal of Chemistry, 1976
Ionization constants, pKa, for a set of 12 phenylazobenzaldoximes (1) have been determined in 50 vol% ethanol–water medium at 25 ± 0.1 °C and a μ of 0.1. Excellent linear correlations are obtained when pKa values are plotted against the substituent constant, σx, and the polar substituent constant, σ*XC6H4, for substituted phenyl groups. The regression
Ahmad S. Shawali, Baheega M. Altahou
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A Critical Compilation of Substituent Constants

1978
The practical usefulness of a correlation equation as well as its significance in theory strongly depend on its range of validity, not only as it is defined but also as its use is restricted in practice by the number of parameters actually known. Hence the tables of parameters are of primary importance and reflect the actual state of a given field.
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Substituent effects on tautomerisation constants of alkylaryltriazenes

Journal of the Chemical Society, Perkin Transactions 2, 1982
Both tautomers of propyl-p-nitrophenyl-, -p-cyanophenyl-, -3,5-dichlorophenyl-, -3,4-dichlorophenyl-, and -p-chlorophenyl-triazenes are directly observable by 1H n.m.r. at 200 MHz in CD3CN at 25 °C. In addition, lower temperature studies enable the two tautomers of propyl-p-methylphenyl- and-p-methoxyphenyl-triazenes to be quantitated.
Migel A. Kelly, Martin Murray, Michael L. Sinnott   +2 more
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Equatorial Contra Axial Polar Substituents. The Relation of a Chemical Reaction to Stereochemical Substituent Constants

The Journal of Organic Chemistry, 2002
The established rates of glycoside hydrolysis reactions were analyzed using free energy relationship plots based on substituent constants that depend on whether the substituent is axial or equatorial. In all cases good correlations were found when assuming either that the transition state had a charged ring-oxygen atom or that it had a charged anomeric
Bols, M., Liang, X., Jensen, Henrik Helligsø   +2 more
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Chemometric Analysis of Substituent Effects. VII. Inductive Effect as a Basic Substituent Effect. Isoeffect Substituent Constant

Collection of Czechoslovak Chemical Communications, 1995
The paper deals with chemometric analysis of the inductive effect. The notion of inductive effect is discussed, and unambiguous definitions are given for the notions of triad: reaction centre-basic skeleton-substituent, and the therewith connected definitions of inductive effect.
Oldřich Pytela, Aleš Halama
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Correlations of force constants for carbonyl out-of-plane deformations with substituent constants

Spectrochimica Acta, 1963
Abstract It is shown that the out-of-plane bending force constants of twenty-two molecules of the type satisfy an empirical relation, where σ I and σ R are respectively Taft's inductive and resonance substituent constants.
J.C. Evans, John Overend
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Substituent Correlations Characterized by Hammett Constants in the Spiropyran–Merocyanine Transition

The Journal of Physical Chemistry A, 2017
The modification of molecular properties by the use of substituents is a versatile route for molecular design. Here we show for the example of multiresponsive spiropyrans that substituent effects and their correlations can be accurately described by Hammett constants, which in turn can be obtained directly from density functional theory calculations ...
Oliver Brügner, Thomas Reichenbach, Michael Sommer, Michael Walter   +3 more
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Determination of Lipophilicity Constants of Sulfonamide Substituents

Journal of Chemical Education, 2001
This article describes a simple laboratory activity using reversed-phase thin-layer chromatography (a stationary nonpolar phase and a mobile polar phase). The Rf values determined for sulfonamides by means of reversed-phase thin-layer chromatography are used to calculate the chromatographic parameter Rm and the lipophilicity constants (π) of different ...
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The taft σI, constants of some phosphoryloxy substituents.

Tetrahedron Letters, 1986
Abstract The Taft's constants of some phosphoryloxy groups were measured by fluorine NMR spectroscopy.
M Julia, J.M Mallet
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