Reaction series not obeying the Hammett equation: conformational equilibria of substituted thiobenzanilides

2002 ◽  
Vol 26 (7) ◽  
pp. 861-866 ◽  
Author(s):  
Karel Palát Jr. ◽  
Stanislav Böhm ◽  
Gabriela Braunerová ◽  
Karel Waisser ◽  
Otto Exner
Keyword(s):  
Hammett Equation ◽  
Reaction Series ◽  
Conformational Equilibria

Substituent effects on the thermodynamic functions of ionization of metasubstituted anilinium ions

1968 ◽  
Vol 21 (4) ◽  
pp. 939 ◽  
Author(s):  
PD Bolton ◽  
FM Hall
Keyword(s):  
Linear Function ◽  
Thermodynamic Functions ◽  
Substituent Effects ◽  
Negative Slope ◽  
Hammett Equation ◽  
Reaction Parameter ◽  
Reaction Series ◽  
Acidity Constants ◽  
Temperature Range ◽  
Relationship Of

Thermodynamic acidity constants of the meta-methoxyanilinium, meta- chloroanilinium, meta-bromoanilinium, and meta-iodoanilinium ions have been measured spectrophotometrically over the temperature range 5-50� and those of the meta-nitroanilinium ion over the temperature range 5-60�. The thermodynamic functions of ionization, ΔG25, ΔH25, ΔS25, and ΔCp,25, have also been calculated for each ion. For a series of seven meta-substituted anilinium ions the acidity constants show close obedience to the Hammett equation over the temperature range 10-50� with the reaction parameter p being a precise linear function of 1/T. The same reaction series also shows a well-defined isoequilibrium relationship of negative slope.

Field and Resonance Components of Substituent Effects in Relation to the Hammett Equation

1972 ◽  
Vol 50 (7) ◽  
pp. 1030-1035 ◽  
Author(s):  
L. D. Hansen ◽  
L. G. Hepler
Keyword(s):  
Substituent Effects ◽  
Similar Reaction ◽  
Hammett Equation ◽  
Reaction Series ◽  
Field Interaction ◽  
Isokinetic Relationship ◽  
Resonance Effects ◽  
Transmission Coefficients ◽  
Substituent Constants ◽  
Specific Reactions

Following Swain and Lupton's analysis of substituent effects, we have taken ΔG0 = aete + artr for a typical substituent effect reaction. In this equation ae and ar are substituent constants for electrostatic field and resonance effects while te and tr are corresponding transmission coefficients. Both substituent constants and tr are taken to be independent of solvent and temperature, while te is taken to depend on both solvent and temperature. General conclusions based on analysis of this model are the following. (i) A Hammett ρσ equation with constant σ values that are valid over a range of temperatures for a variety of reactions in several solvents can be obtained only when either the field or the resonance interaction is negligible compared with the other. (ii) A Hammett ρσ equation can be expected to hold for "similar" reaction series in a given solvent at one temperature even when both the field and resonance interactions are important, (iii) An isoequilibrium or isokinetic relationship can be expected only when the field interaction is dominant.The general equations leading to these and other conclusions are presented so that one can later insert appropriate mathematical descriptions of detailed models and thereby obtain information about specific reactions.

Substituent Effects on Conformational Equilibria: Substituted Thiobenzanilides

1999 ◽  
Vol 64 (8) ◽  
pp. 1295-1306 ◽  
Author(s):  
Karel Waisser ◽  
Karel Palát ◽  
Otto Exner
Keyword(s):  
Absorption Spectra ◽  
Infrared Absorption ◽  
Substituent Effects ◽  
Hammett Equation ◽  
Absorption Intensity ◽  
Conformational Equilibria ◽  
Benzene Rings ◽  
Infrared Absorption Spectra

Infrared absorption spectra of 38 thiobenzanilides in tetrachloromethane solutions were recorded in the ν(N-H) region. From the integrated absorption intensity of the computer-resolved N-H bands, the abundance of the Z and E conformations was calculated. The values of pertinent log KC depend on substitution in an unexpected way which cannot be described by the Hammett equation or by any other known type of modified constants σ. The only regularity observed is that the substituent effects from the two benzene rings of thioanilide are additive with a remarkable precision. The ν(N-H) frequencies are not much sensitive to substitution and the dependence is not simple: only ν(N-H) of the E conformer depend on substitution in a regular way.

THE APPLICATION OF THE HAMMETT EQUATION TO ORTHO-SUBSTITUTED BENZENE REACTION SERIES

1960 ◽  
Vol 38 (12) ◽  
pp. 2493-2499 ◽  
Author(s):  
Marvin Charton
Keyword(s):  
Benzene Ring ◽  
Substituent Effects ◽  
Para Position ◽  
Steric Effects ◽  
Side Chain ◽  
Ortho Position ◽  
Reaction Site ◽  
Hammett Equation ◽  
Reaction Series ◽  
Electrical Effect

The Hammett equation is directly applicable to ortho-substituted benzene reaction series in which reaction site and benzene ring are separated by some group Z, apparently due to the absence of steric effects in these series. The σp values are used in the correlations. Fourteen ortho-substituted benzene reaction series have been correlated. The electrical effect of a substituent in the ortho position is found to be about 0.75 times its effect in the para position. The effect of the side-chain Z in the transmission of substituent effects is OCH2 > SCH2 > CH = CH > SeCH2 > CH2CH2.

Concerning the Problem of the Isokinetic Relationship. III. The Temperature-Dependance of the hammett Equation

1985 ◽  
Vol 38 (5) ◽  
pp. 677 ◽  
Author(s):  
W Linert ◽  
R Schmid ◽  
AB Kudrjawtsev
Keyword(s):  
Benzoic Acid ◽  
Hammett Equation ◽  
Reaction Series ◽  
Temperature Dependent ◽  
Isokinetic Relationship ◽  
A Value ◽  
The Common ◽  
Point Of Intersection ◽  
Temperature Dependance ◽  
The Relationship

It is shown that the temperature-dependence of the Hammett equation is, in contrast to tradition, both physically and experimentally better described by means of temperature-dependent σ and temperature- independent ρ (termed ρo). The relationship between ρo and the customary (temperature dependent) ρ is ρT = ρo(1/T-1/Tbiso)/(1/T-1/Tbiso) where Tbiso , is the isoequilibrium temperature of the benzoic acid ionization, for which the present analysis suggests a value of -255 K, and T is 298 K. In these terms, the temperature variation of the Hammett equation can be evaluated by supplying merely E(u)a (the activation energy for the reaction of the unsubstituted reactant) and ρo, in that the σ value for the isokinetic substituent , i.e., the abscissa of the common point of intersection in the Hammett plot, is σiso = (1/T-1/Tbiso)E(u)a/(2.303Rρo) = E(u)a/(2630po) Further, ρo I related to energies ρo = E(u)a/(ΔH°u-ΔH°s(iso))where ΔH°u and ΔH°s(iso) are the ionization enthalpies of the parent benzoic acid and that bearing the isokinetic substituent , respectively. Analogous equations apply to thermodynamic reaction series when substituting E(u)a for ΔH°u(series). Along these lines the interpretation of the customary Hammett plot is advanced.

HANDS ON BOWENS REACTION SERIES

2019 ◽  
Author(s):  
Steve Carlson ◽  
Keyword(s):  
Reaction Series ◽  
Hands On

Solvolysis kinetics and mechanism of substituted 3-acetyl-1,3-diphenyltriazenes in acid medium; Kinetic acidity function

1987 ◽  
Vol 52 (9) ◽  
pp. 2212-2216
Author(s):  
Oldřich Pytela ◽  
Martin Kaska ◽  
Miroslav Ludwig ◽  
Miroslav Večeřa
Keyword(s):  
Acid Medium ◽  
Sulphuric Acid ◽  
Rate Constants ◽  
Decomposition Kinetics ◽  
Acidity Function ◽  
Hammett Equation ◽  
Kinetic Acidity ◽  
Reaction Constant ◽  
Acid Catalyzed ◽  
Catalytic Rate

The decomposition kinetics has been measured of fourteen 3-acetyl-1,3-bis(subst. phenyl)triazenes in 40% (v/v) ethanol and sulphuric acid. The kinetic acidity function and catalytic rate constants have been determined from the rate constants observed. Mechanism has been suggested for the general acid-catalyzed solvolysis from comparison of the course of the kinetic acidity function and H0 function and from the reaction constant of the Hammett equation.

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