Solvation and steric hindrance in methyl-substituted benzoic acids

Kulhánek, Jiří; Exner, Otto

doi:10.1039/a800623g

Cited by 13 publications

(13 citation statements)

References 29 publications

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“…The experimental pK a values have been taken mainly from the series of papers by Pytela et al [15 -20], Bosch and coworkers [21,22], the Izutsku compilation [23], Kolthoff and coworkers [24,25], and others [7,26]. The 136 benzoic acids contain different substituents in the aromatic ring, and besides the benzoic acid itself there are 49 mono-, 68 di-, 14 tri-, 3 tetra-, and 1 penta-substituted compounds.…”

Section: Data Setmentioning

confidence: 99%

QSPR Prediction of pK_a for Benzoic Acids in Different Solvents

2008

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A Computational Neural Network (CNN) derived model is proposed for the pK a prediction of benzoic acids in different solvents. The system studied contains 519 pK a values corresponding to 136 benzoic acids determined in water and in 8 organic solvents. The benzoic acids were described by the usual molecular descriptors and the solvents by a number of physical properties and by several parameters of the most widely used polarity solvent scales. The model is composed of seven descriptors -five of them corresponding to the solute and the other two to the solvents -and was validated by an external prediction set. The three sets of values needed in the analysis, training, prediction, and cross-validation, have the same squared correlation coefficient (0.998) and Root-Mean Square Error (RMSE) (0.21) values. The robustness of the model is also given for the statistical results for small subsets, such as ortho-and non-ortho-substituted acids, those obtained in protic or aprotic solvents, those obtained in each solvent, and even those for the set of pK a values of one specific acid in several solvents. The descriptors encode information about the chemical nature of the solutes and the solvents that is clearly related to the interactions present in the dissociation process in solution. The derived model also has the ability to predict pK a values of a larger set of aromatic neutral acids, containing both phenols and benzoic acids.

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Section: Data Setmentioning

confidence: 99%

QSPR Prediction of pK_a for Benzoic Acids in Different Solvents

2008

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“…Steric effect research has seen major advances in the last decade, with important contributions from Exner's group. [1][2][3][4][5][6][7][8][9][10][11][12] This paper focuses on several aspects of the o-hydroxyaryl Schiff bases research. The paper focuses on the intramolecular hydrogen bond of the O-HÁ Á ÁN type which forms between the hydroxyl group of the phenol ring (the proton donor) and the nitrogen atom of the imine (the proton acceptor) (Scheme 1).…”

Section: Introductionmentioning

confidence: 99%

Intramolecular hydrogen bonding in o‐hydroxyaryl Schiff bases

Filarowski

2005

J of Physical Organic Chem

122

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This review deals with selected aspects of research on o-hydroxyaryl Schiff bases. Special attention is given to results obtained by x-ray, IR, UV and NMR spectroscopic methods and quantum-mechanical calculations that allow a better understanding of the nature of o-hydroxyaryl Schiff bases. The paper reports on studies of sterically modified o-hydroxyaryl Schiff bases with an intramolecular hydrogen bond made short owing to steric repulsion. The following points are focused upon: structural and energetic analysis of the steric effect and its influence on the hydrogen bond length; proton localization and the proton transfer process; the impact of proton transfer on the chelate and phenol rings in the intramolecular hydrogen bond; a generalized scheme of tautomer equilibrium and its study with the use of experimental and theoretical methods; some discrepancies found in standard parameters for a particular tautomeric form; calculations of the potential energy curve for basic tautomer forms; influence of the steric effect on the potential curve shape; and a review of semi-empirical and quantum-mechanical calculations of molecular structures in the ground state.

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“…However, the situation is complicated by nonbonding interactions between the reaction centre and ortho substituent, which is usually referred to as "ortho effect" (for a survey see refs 1,2,6-10 , see also series in refs [11][12][13][14][15][16][17][18] ). The term "effect" is not quite precise since the ortho effect involves several effects, in particular hydrogen bond formation between certain atoms of the reaction centre and substituent 10 , steric interaction between the solvated reaction centre and solvated substituent 19 , changes in resonance interaction 20 and other less important factors 21 . The extent of operation of the effects mentioned specifically depends on the chemical structure of the reaction centre, its chemical neighbourhood, and the medium used 22 .…”

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confidence: 99%

Chemometric Analysis of Substituent Effects. XII. Application of Relationship Between 2- and 4-Substitution of Benzene Ring to Study ortho Effect in Selected Compounds with Different Reaction Centres

Pytela¹,

Prusek²

1999

Collect. Czech. Chem. Commun.

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Dedicated to Professor Otto Exner on the occasion of his 75th birthday in recognition of his outstanding contributions to the areas of physical organic chemistry and chemometrics.Three model compounds have been selected to study the relationship between ortho and para substitution: benzoic acid, phenol, and aniline. Sixteen substituents have been chosen involving also those capable of potential interaction between ortho substituent and the reaction centre. For the combinations given, literature presents 25 pairs of data obtained by measuring a particular process for both the ortho and para substituted derivatives. The missing dissociation constants of 16 ortho substituted benzoic acids in water and ethanol and 16 para substituted benzoic acids in dimethyl sulfoxide and pyridine have been measured by potentiometric titration. The data matrices were submitted to analysis by the methods of projection of latent structures (PLS) and principal component analysis (PCA). It has been found that the substituent effects from ortho and para positions have the same character unless the ortho substituents interact with the reaction centre. Such interactions can change the experimentally found value by as much as 20% of its magnitude. The most significant interaction is a hydrogen bond formation. Out of the three models studied the most extensive interactions are present in benzoic acid, whereas almost none were observed in aniline. The capability of donation of electron pair to a hydrogen bond decreases in the substituent series COCH 3 > SO 2 CH 3 > NO 2 . The capability of donation of proton to a hydrogen bond with electron-pair donor decreases in the substituent series OH > NHCOCH 3 ≈ SH > NH 2 > SO 2 NH 2 .The ortho and para positions of the aromatic nucleus are alternating positions and, therefore, it is justifiably presumed 1,2 that the substituent effect transferred by valence electrons from both positions is of identical nature,

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Solvation and steric hindrance in methyl-substituted benzoic acids

Cited by 13 publications

References 29 publications

QSPR Prediction of pK_a for Benzoic Acids in Different Solvents

QSPR Prediction of pK_a for Benzoic Acids in Different Solvents

Intramolecular hydrogen bonding in o‐hydroxyaryl Schiff bases

Chemometric Analysis of Substituent Effects. XII. Application of Relationship Between 2- and 4-Substitution of Benzene Ring to Study ortho Effect in Selected Compounds with Different Reaction Centres

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Solvation and steric hindrance in methyl-substituted benzoic acids

Cited by 13 publications

References 29 publications

QSPR Prediction of pKa for Benzoic Acids in Different Solvents

QSPR Prediction of pKa for Benzoic Acids in Different Solvents

Intramolecular hydrogen bonding in o‐hydroxyaryl Schiff bases

Chemometric Analysis of Substituent Effects. XII. Application of Relationship Between 2- and 4-Substitution of Benzene Ring to Study ortho Effect in Selected Compounds with Different Reaction Centres

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QSPR Prediction of pK_a for Benzoic Acids in Different Solvents

QSPR Prediction of pK_a for Benzoic Acids in Different Solvents