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 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.

Separation of the Enthalpic and Entropic Contributions to Substituent Effects for the Equilibrium Constants of Aromatic Acids

1975 ◽  
Vol 53 (23) ◽  
pp. 3622-3633 ◽  
Author(s):  
T. M. Krygowski ◽  
W. R. Fawcett
Keyword(s):  
Substituent Effect ◽  
Equilibrium Constants ◽  
Substituent Effects ◽  
Point Of View ◽  
Aromatic Acids ◽  
Resonance Effects ◽  
Equation Analysis ◽  
Reaction Constant ◽  
Enthalpy And Entropy Changes ◽  
Substituent Constants

Separation of the substituent effect ρσ into entropie ρSσS and enthalpic ρHσH contributions is presented within the framework of the general Hammett equation. Analysis of the experimental data for aromatic acids shows that, in general, entropie effects are the major contribution to the total substituent effect, the entropic reaction constant being approximately equal to the normal Hammett ρ A comparison of the present results with those based on a separation of inductive and resonance effects shows that the entropie and inductive effects are directly related. On the other hand, strongly resonance interacting substituents were found to be enthalpy controlled. The substituent effect on enthalpy and entropy changes is discussed from a molecular point of view and related to inductive and resonance effects. A list of 16 enthalpic (σH) and entropie (σS) substituent constants are presented.

Chemometrical Analysis of Substituent Effects. IV. Additivity of Substituent Effects in Dissociation of 3,5-Disubstituted Benzoic Acids in Organic Solvents

1994 ◽  
Vol 59 (7) ◽  
pp. 1637-1644 ◽  
Author(s):  
Oldřich Pytela ◽  
Jiří Kulhánek ◽  
Miroslav Ludwig
Keyword(s):  
Organic Solvents ◽  
Dissociation Constants ◽  
Quantitative Description ◽  
Substituent Effects ◽  
Benzoic Acids ◽  
Hammett Equation ◽  
Specific Solvation ◽  
Reaction Constant ◽  
Substituent Constants ◽  
The Individual

Ten 3,5-disubstituted benzoic acids have been synthesized containing all possible combinations of the following substituents: CH3O, CH3, Cl/Br, NO2. The dissociation constants of these acids have been measured in seven organic solvents (methanol, acetone, dimethyl sulfoxide, dimethylformamide, acetonitrile, pyridine, 1,2-dichloroethane). It has been found that the effect of disubstitution is smaller than that due to interaction of substituents or their solvation and represents only about 0.2% of the effect caused by the individual substituents. The additivity in 3,5-disubstitution is about 2 - 3 times as good as that in 3,4-disubstitution. The quantitative description of substituent effects at the 3 and 5 positions is additive within the range of validity of the Hammett equation irrespective of the type of the substituent constants adopted, the addition of the multiplicative term being statistically insignificant. The solvent effect on 3,4- and 3,5-disubstituted derivatives is somewhat different at the same value of the reaction constant, due predominantly to the specific solvation of the 4-CH3O and 4-NO2 groups.

Chemometric Analysis of Substituent Effects. VI. A Study of ortho Effect in Dissociation of 2,6-Disubstituted Benzoic Acids

1995 ◽  
Vol 60 (5) ◽  
pp. 829-840 ◽  
Author(s):  
Jiří Kulhánek ◽  
Oldřich Pytela
Keyword(s):  
Latent Variables ◽  
Dissociation Constants ◽  
Additive Model ◽  
Substituent Effects ◽  
Point Of View ◽  
Steric Effects ◽  
Benzoic Acids ◽  
Hammett Equation ◽  
Substituent Constants ◽  
Substituted Benzoic Acids

Ten 2,6-disubstituted benzoic acids have been synthesized containing all possible combinations of the following substituents: CH3, OCH3, Cl, and NO2. The dissociation constants of these acids have been measured by potentiometric titration in methanol, acetone, dimethyl sulfoxide, dimethylformamide, acetonitrile, pyridine, and 1,2-dichloroethane. The experimental data obtained together with the pK values of 2-substituted benzoic acids in the same solvents have been analyzed from the point of view of ortho effect and additivity of disubstitution. The mutual interaction between substituents was found to represent only 0.12% of the variability due to substitution and to contribute to the overall variability of data less than the interaction between the substituent and solvent by a factor of about 13. The analysis of data by the method of multiple linear regression revealed a contribution of steric effects beside the effects transmitted through the aromatic skeleton. The 2- and 6-substituents effects are additive within the validity of the Hammett equation, and an addition of a multiplicative term describing interactions between the substituents is statistically insignificant. Nonlinear regression has been adopted in the additive model with multiplicative term to find the inner substituent constants including all the effects of substituents from ortho position: the term describing the interaction between 2- and 6-substituents is statistically insignificant in this model. An application of the method of conjugated deviations revealed two statistically significant latent variables. The first one explains 91.5% of the variability of data and is connected with the substituent effects transmitted through the aromatic skeleton. The second one explains 7.5% of variability of data and predominantly reflects the steric effects of substituents.

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.

Chemometric Analysis of Substituent Effects. II. Relation Between Hammett Substituent Constants σm and σp and a New Model for Quantitative Description of Substituent Effects

1994 ◽  
Vol 59 (2) ◽  
pp. 381-390 ◽  
Author(s):  
Oldřich Pytela
Keyword(s):  
Dissociation Constants ◽  
General Relation ◽  
Quantitative Description ◽  
Substituent Effects ◽  
Data Series ◽  
Reaction Centre ◽  
Substituent Constant ◽  
New Model ◽  
Resonance Effects ◽  
Substituent Constants

The paper presents values of 25 substituent constants σi obtained by optimizing 46 data series of dissociation constants of substituted benzoic acids in various media. The constants σi fulfil the general relation between the substituent constants of the Hammett type in meta and para positions enabling the description of substituent effects from both positions at the same time by a single constant. The Hammett substituent constants are interpreted by means of the σi constants with an accuracy better than 0.03 units. In addition to it, the validity of general relationship between σp and σm was verified on a set of 56 substituents with the prediction accuracy of 0.06 units for σp, and after excluding the probably incorrectly parametrized substituents NHCOC6H5, CH3S, and F the accuracy has improved to 0.05 units (98% of interpreted variability). The given relationship has served as a basis for suggesting a new model of transfer of substituent effects to a reaction centre: the model involves both the Hammett equation and the Yukawa-Tsuno equation and explains their background. The suggested model uses generalized transmission coefficients to separately describe the transformation of a single primary substituent effect - depending on its structure - into one inductive and two resonance effects which are transmitted through two independent channels to the reaction centre and here transformed into the resulting observable effect. From the model it follows that the substituent constant σp is not a substituent constant in the true sense of the word since it involves the characteristics of skeleton and of reaction centre.

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.

scholarly journals The substituent effects on the 13c chemical shifts of the azomethine carbon atom of n-(phenyl substituted) salycilaldimines

2012 ◽  
Vol 77 (8) ◽  
pp. 993-1001
Author(s):  
Sasa Drmanic ◽  
Aleksandar Marinkovic ◽  
Jasmina Nikolic ◽  
Bratislav Jovanovic
Keyword(s):  
Carbon Atom ◽  
Schiff Bases ◽  
13C Nmr ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
13C Chemical Shifts ◽  
Resonance Effects ◽  
Inductive Effects ◽  
Substituent Constants ◽  
Significant Resonance

The Hammett correlations between 13C-NMR chemical shifts of the azomethine carbon atom and the corresponding substituent constants for thirtheen Schiff bases were established. Successful correlation of the chemical shifts with electrophilic substituent constants ?+ indicate significant resonance interaction of the substituents on the aniline ring with the azomethine carbon atom in the examined series of imines. The demand for electrons in the investigated compounds was compared to that of the N-benzylidenanilines and N-(phenyl substituted) pyridinealdimines. The way of transmission of the substituent effects was discussed and they are separated into resonance and inductive effects. Inductive effects prevail over resonance effects.

Substituent effects in 1,3-indanediones

1982 ◽  
Vol 47 (5) ◽  
pp. 1486-1493 ◽  
Author(s):  
Alexander Perjéssy
Keyword(s):  
Substituent Effects ◽  
Empirical Equations ◽  
Substituent Constants ◽  
Complex Structural

The carbonyl stretching frequencies correlate well with substituent constants in a series of 166 1,3-indanediones using improved and extended Seth-Paul-Van Duyse equation. Transmissive factors and group electronegativities have been used to find empirical equations for calculation of substituent constants of more complex structural fragments.

Kinetic study of hydrolysis of benzoates. part xxvii. ortho substituent effect in alkaline hydrolysis of phenyl esters of substituted benzoic acids in aqueous Bu4NBr

2009 ◽  
Vol 74 (1) ◽  
pp. 29-42 ◽  
Author(s):  
Vilve Nummert ◽  
Mare Piirsalu ◽  
Signe Vahur ◽  
Oksana Travnikova ◽  
Ilmar A. Koppel
Keyword(s):  
Alkaline Hydrolysis ◽  
Rate Constants ◽  
Pure Water ◽  
Substituent Effects ◽  
Benzoic Acids ◽  
Resonance Effects ◽  
The Media ◽  
Substituted Benzoic Acids ◽  
Hydrolysis Of ◽  
Ortho Substituent

The second-order rate constants k (in dm3 mol–1 s–1) for alkaline hydrolysis of phenyl esters of meta-, para- and ortho-substituted benzoic acids, X-C6H4CO2C6H5, have been measured spectrophotometrically in aqueous 0.5 and 2.25 M Bu4NBr at 25 °C. The substituent effects for para and meta derivatives were described using the Hammett relationship. For the ortho derivatives the Charton equation was used. For ortho-substituted esters two steric scales were involved: the EsB and the Charton steric (υ) constants. When going from pure water to aqueous 0.5 and 2.25 M Bu4NBr, the meta and para polar effects, the ortho inductive and resonance effects in alkaline hydrolysis of phenyl esters of substituted benzoic acids, became stronger nearly to the same extent as found for alkaline hydrolysis of C6H5CO2C6H4-X. The steric term of ortho-substituted esters was almost independent of the media considered. The rate constants of alkaline hydrolysis of ortho-, meta- and para-substituted phenyl benzoates (X-C6H4CO2C6H5, C6H5CO2C6H4-X) and alkyl benzoates, C6H5CO2R, in water, 0.5 and 2.25 M Bu4NBr were correlated with the corresponding IR stretching frequencies of carbonyl group, (ΔνCO)X.

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