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.

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.

Chemometrical Analysis of Substituent Effects. V. ortho Effect

1994 ◽  
Vol 59 (9) ◽  
pp. 2005-2021 ◽  
Author(s):  
Oldřich Pytela ◽  
Josef Liška
Keyword(s):  
Dissociation Constants ◽  
Substituent Effects ◽  
Reaction Centre ◽  
Benzoic Acids ◽  
Electronic Effects ◽  
Substituent Constant ◽  
Zero Values ◽  
Substituent Constants ◽  
Substituted Benzoic Acids ◽  
Intramolecular Hydrogen

The dissociation constants of nineteen ortho substituted benzoic acids have been determined in eight organic solvents (methanol, ethanol, acetone, dimethyl sulfoxide, dimethylformamide, acetonitrile, pyridine, 1,2-dichloroethane). The correlation between the σI, σR, and υ constants were unsuccessful due to neglecting the description of intramolecular hydrogen bond effect. The method of conjugated deviations has been applied to the results obtained and to those given in literature for ortho substituted benzoic acids (the dissociation constants, the reaction with diphenyldiazomethane, 33 sets), and values of three types of substituent constants have been determined for 29 substituents. The first of these substituent constants, σoi, describes the electronic effects and was adjusted with the application of the isoparameter relation (σoi as a function of σmi) suggested in previous communications. This constant (after excluding the substituents NHCOCH3 and OCOCH3) correlates very well (R = 0.993) with the σI and σR constants. The second substituent constant, σHGi, describes the interaction of the reaction centre (the oxygen atom of carboxylate anion) with the substituent, and it has non-zero values for the substituents OH, SH, NH2, NHCH3, NHCOCH3, COOH, CONH2, and SO2NH2. The third substituent constant, σSi, describes the steric effects and is not significantly related to any of the known quantities of this type. The set given was tested together with the triad of σI, σR, and υ on the definition set and on a set extended by other 28 sets of processes with ortho substituted compounds. On the whole, the set of substituent constants suggested explains 94.6% of variability of data, whereas only 66.0% are explained with the use of σI, σR, and u constants. Moreover, the tests have shown that the σoi constant is not suitable for interpretations of processes involving direct conjugation between the reaction centre and substituent.

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.

The Determination of Substituent Effects by 13C Nuclear Magnetic Resonance Spectrometry. The Effect of Solvent on CH2X Groups

1985 ◽  
Vol 38 (2) ◽  
pp. 337
Author(s):  
DAR Happer ◽  
BE Steenson
Keyword(s):  
Inductive Effect ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Side Chain ◽  
Polar Solvents ◽  
13C Nuclear Magnetic Resonance ◽  
Nuclear Magnetic Resonance Spectrometry ◽  
Magnetic Resonance Spectrometry ◽  
Lines Of Force

A previous study of the effect of meta- and para-CH2X substituents on the 13C n.m.r. chemical shifts of the α and β side-chain carbons of β- methoxycarbonylstyrenes (methyl cinnamates ) in ethanol has been extended to cover five additional solvents (Me2SO, Me2CO, CDCl3, CCl4 and C6H6). The results support the earlier claim that, for most substituents , the magnitudes of the substituent -induced shifts are proportional to the inductive effect of X. The major contributor to the latter appears to be the field effect generated by the C-X dipole, with the lines of force passing mainly through the molecule. In non-polar solvents, however, there is evidence that lines of force passing directly through the solvent can also influence the shifts in both the meta and para series.

Substituent effects by carbon-13 nuclear magnetic resonance: Concerning the π-inductive effect

1974 ◽  
Vol 27 (8) ◽  
pp. 1817 ◽  
Author(s):  
W Adcock ◽  
M Aurangzeb ◽  
W Kitching ◽  
N Smith ◽  
D Doddrell
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Inductive Effect ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Suitable Model ◽  
Nuclear Magnetic

13C Substituent chemical shifts (scs) data for the C4 and C10 carbon atoms in 1-x-naphthalenes and 9-x-anthracenes respectively do not corroborate the proposal that the meso disposition in anthracene is a suitable model for the detection of the π-inductive or inductomesomeric effect.

Substituent Effects on the Base-Catalysed Hydrolysis of Phenyl Esters of ortho-Substituted Benzoic Acids

2001 ◽  
Vol 66 (5) ◽  
pp. 770-784 ◽  
Author(s):  
Ingrid Bauerová ◽  
Miroslav Ludwig
Keyword(s):  
Substituent Effects ◽  
Uv Spectrophotometry ◽  
Reaction Centre ◽  
Benzoic Acids ◽  
Model Compounds ◽  
Pseudo First Order Reaction ◽  
Reaction Conditions ◽  
Substituted Benzoic Acids ◽  
Kinetics Of ◽  
Hydrolysis Of

Fourteen model phenyl esters of 2-substituted benzoic acids were synthesised. Structures and purity of model compounds were confirmed by 1H and 13C NMR spectroscopy, as well as by HPLC and elemental analysis. Kinetics of base-catalysed hydrolysis of model phenyl esters occurring by the BAc2 mechanism were measured by UV spectrophotometry in 50% (v/v) aqueous dimethyl sulfoxide solutions at 25 °C under pseudo-first-order reaction conditions (c(NaOH) = 0.001-1.0 mol l-1). Linear relation between J-E and log kobs with the slope close to unity was found for all model compounds. Neither one-parameter nor multiparameter Hammett-type description of variability of experimental data obtained for phenyl esters of 2-substituted benzoic acids was found. Two groups (conjugating and non-conjugating) were created by division of ortho-substituents in ortho-position using the AISE theory, based on their interaction with the reaction centre.

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