Substituent effects on the ionization constants of phenylazobenzaldoximes

1976 ◽  
Vol 54 (20) ◽  
pp. 3260-3266 ◽  
Author(s):  
Ahmad S. Shawali ◽  
Baheega M. Altahou
Keyword(s):  
Substituent Effects ◽  
Solution Phase ◽  
Ionization Constants ◽  
Water Medium ◽  
Hammett Equation ◽  
Substituent Constant ◽  
Polar Substituent ◽  
Linear Correlations

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 lines are: pKa = 9.905–0.737σX; and pKa = 10.489 − 1.01σ* XC6H4 respectively. The pKa values have also been correlated with the extended Hammett equation. The correlation follows the equation: PKa =9.987 − 0.713σI,X−0.734 σR,X. It is concluded that EE and ZE forms of 1 exist in equilibrium in solution phase.

Effects of Bromine Substituents on Rates of Acetate-promoted Enolization of Ketones

1972 ◽  
Vol 50 (19) ◽  
pp. 3242-3247 ◽  
Author(s):  
R. A. Cox ◽  
J. Warkentin
Keyword(s):  
Transition State ◽  
Carbonyl Group ◽  
Substituent Effects ◽  
Steric Effects ◽  
Ionization Constants ◽  
Polar Substituent ◽  
Methylene Group ◽  
Better Than

Effects of bromine substituents on rates of acetate-catalyzed bromination of ketones are reported. Approximate polar contributions to the rates were obtained, based on the approximation that the steric effects of bromine and methyl are identical. Such polar substituent effects are quite large at the α′-position of an α-bromo ketone, leading to the conclusion that the carbonyl group is much better than the methylene group in transmitting polar effects.Rate enhancements caused by α-bromine substituents are largely entropic in origin and rates correlate well with ionization constants of α-bromo acids. These results are interpreted as indicative of an enolate-like transition state for acetate-catalyzed enolization.

Chemometric Analysis of Substituent Effects. VIII. Alternative Interpretation of Substituent Effects (AISE)

1995 ◽  
Vol 60 (9) ◽  
pp. 1502-1528 ◽  
Author(s):  
Oldřich Pytela
Keyword(s):  
Multiple Bond ◽  
Substituent Effects ◽  
Alternative Interpretation ◽  
Class I ◽  
Reaction Centre ◽  
Correlation Equations ◽  
Class Iii ◽  
Substituent Constant ◽  
Chemical Models ◽  
The Individual

Alternative interpretation of substituent effects (AISE) starts from the presumption that a substituent only possesses a single property described by a single substituent constant. This property is transmitted to the reaction centre by three different ways depending on the interaction type in the triad reaction centre - basic skeleton - substituent. For interpretation it is substantial whether or not the substituent has p electrons at the atom adjacent to the basic skeleton. If it has none, the substituent belongs to class I and operates only by its basic effect described by the mentioned single substituent constant. Substituents of class II possess a free electron pair at the atom adjacent to the basic skeleton, and those of class III have a multiple bond between the first and the second atoms which is polarized in the direction from the basic skeleton. Substituent effects in class I are described by a substituent constant identical with σI constant. Substituents in classes II and III show additional effects proportional to the same constant. Hence, a separate treatment of substituent effects in the individual classes provides three straight lines intersecting in a common point. Mathematically, the description of substituent effects in this approach is expressed by a family of lines with a single explaining variable. The point of intersection, which is referred to as the iso-effect point, is not identical with the classic standard substituent - hydrogen - but is near to CN substituent. The approach given has the advantage of adopting a single substituent constant whose scale can be adjusted relatively precisely. Its drawback (like in the case of the correlation equations derived from the principle of separation of substituent effects) lies in a more extensive set of substituents needed for a correlation. The AISE principle has been applied to 318 series of experimental data describing effects of 32 substituents in a large variety of chemical models (aliphatic, alicyclic, aromatic, heteroaromatic, with or without direct conjugation between reaction centre and substituent) in both chemical reactions and equilibria. A comparison with two other correlation relations with two and three substituent constants for interpretation of substituent effects based on the principle of separation of the individual substituent effects showed that the closeness of AISE based correlations is comparable with that of the correlation equations currently used. It was somewhat less successful in the models with direct conjugation between reaction centre and substituent but the AISE principle can be used even in these cases.

Chemometric Analysis of Substituent Effects. VII. Inductive Effect as a Basic Substituent Effect. Isoeffect Substituent Constant

1995 ◽  
Vol 60 (8) ◽  
pp. 1316-1332 ◽  
Author(s):  
Oldřich Pytela ◽  
Aleš Halama
Keyword(s):  
Inductive Effect ◽  
Chemical Shifts ◽  
Quantitative Description ◽  
Substituent Effects ◽  
Intersection Point ◽  
Chemometric Analysis ◽  
Reaction Centre ◽  
Substituent Constant ◽  
Modified Method ◽  
Substituted Benzoic Acids

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. For a quantitative description of inductive effect 7 types of chemical models were selected including noncyclic compounds, cyclic, and bicyclic compounds, derivatives of quinuclidine, 3-substituted benzoic acids, sulfonamides and pyridines. Altogether 139 sets of experimental data from literature have been used including altogether 1 294 points (9.3 points per set, 5 points at least) reflecting substituent effects of 34 substituents. It has been found that for a standard model the dissociation of substituted bicycloalkanecarboxylic acids only is satisfactory, all the other models reflecting also the mesomeric effects to variable extent (up to 10%). A distinctly different substitution behaviour was observed with 19F and 13C NMR chemical shifts of 4-substituted 1-fluoro- or 1-methylbicyclo[2.2.2]octanes. The earlier suggested model of substituent effects based on different way of transmission of substituent effects (3 classes) has been used for separating the inductive and mesomeric effects: it is mathematically presented as a set of straight lines with the intersection point at the so-called isoeffect substituent constant. Using the modified method of conjugated deviations a chemometric scale has been created for the inductive effect which agrees very well with the conventional scales given in literature; the only differences were observed for F and CH=O substituents (which are overestimated and underestimated, respectively, in literature). In the context given the inductive effect appears as a fundamental quantity forming a basis for quantitative description of other effects transferred by electrons.

ChemInform Abstract: POLAR SUBSTITUENT EFFECTS IN ADDITIONS OF ALKYL RADICALS TO ALKENES

1981 ◽  
Vol 12 (37) ◽  
Author(s):  
B. GIESE ◽  
J. MEIXNER
Keyword(s):  
Substituent Effects ◽  
Alkyl Radicals ◽  
Polar Substituent

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.

Polar substituent effects on13C NMR spectra in ethylcis-2-substituted cyclopropane carboxylates

1982 ◽  
Vol 20 (3) ◽  
pp. 159-161 ◽  
Author(s):  
Yoshiaki Kusuyama ◽  
Satoru Inoshita ◽  
Ginjiro Okada ◽  
Minoru Yanagi ◽  
Kenjiro Tokami ◽  
...  
Keyword(s):  
Nmr Spectra ◽  
Substituent Effects ◽  
Polar Substituent

Polar substituent effects in the solvolysis of 2-methyl-2-exo-norbornyl 2,4-dinitrophenyl ethers

1980 ◽  
Vol 21 (46) ◽  
pp. 4433-4436 ◽  
Author(s):  
C.A. Grob ◽  
A. Waldner
Keyword(s):  
Substituent Effects ◽  
Polar Substituent

4-Substituted quinuclidinium perchlorates in the determination of polar substituent effects

1973 ◽  
Vol 14 (37) ◽  
pp. 3627-3630 ◽  
Author(s):  
E. Ceppi ◽  
W. Eckhardt ◽  
C.A. Grob
Keyword(s):  
Substituent Effects ◽  
Polar Substituent
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