Quantitative evaluation of polar ortho-substituent effects

1968 ◽  
pp. 338 ◽  
Author(s):  
Charles L. Liotta
Keyword(s):  
Quantitative Evaluation ◽  
Substituent Effects ◽  
Ortho Substituent

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.

Ortho-Substituent Effects on Diphenylurea Packing Motifs

2017 ◽  
Vol 17 (10) ◽  
pp. 5065-5072 ◽  
Author(s):  
Marina A. Solomos ◽  
Taylor A. Watts ◽  
Jennifer A. Swift
Keyword(s):  
Substituent Effects ◽  
Ortho Substituent

scholarly journals Prediction of ortho substituent effect in alkaline hydrolysis of phenyl esters of substituted benzoic acids in aqueous acetonitrile

2013 ◽  
Vol 11 (12) ◽  
pp. 1964-1975 ◽  
Author(s):  
Vilve Nummert ◽  
Mare Piirsalu ◽  
Ilmar Koppel
Keyword(s):  
Alkaline Hydrolysis ◽  
Rate Constants ◽  
Substituent Effect ◽  
Substituent Effects ◽  
Benzoic Acids ◽  
Aqueous Acetonitrile ◽  
Substituent Constants ◽  
Substituted Benzoic Acids ◽  
Hydrolysis Of ◽  
Ortho Substituent

AbstractThe second-order rate constants k for the alkaline hydrolysis of phenyl esters of meta-, para- and ortho-substituted benzoic acids, X-C6H4CO2C6H5, in aqueous 50.9% acetonitrile have been measured spectrophotometrically at 25°C. The log k values for meta and para derivatives correlated well with the Hammett σm,p substituent constants. The log k values for ortho-substituted phenyl benzoates showed good correlations with the Charton equation, containing the inductive, σI, resonance, σ○ R, and steric, E s B, and Charton υ substituent constants. For ortho derivatives the predicted (log k X)calc values were calculated with equation (log k ortho)calc = (log k H AN)exp + 0.059 + 2.19σI + 0.304σ○ R + 2.79E s B − 0.0164ΔEσI — 0.0854ΔEσ○ R, where DE is the solvent electrophilicity, ΔE = E AN — E H20 = −5.84 for aqueous 50.9% acetonitrile. The predicted (log k X)calc values for phenyl ortho-, meta- and para-substituted benzoates in aqueous 50.9% acetonitrile at 25°C precisely coincided with the experimental log k values determined in the present work.The substituent effects from the benzoyl moiety and aryl moiety were compared by correlating the log k values for the alkaline hydrolysis of phenyl esters of substituted benzoic acids, X-C6H4CO2C6H5, in various media with the corresponding log k values for substituted phenyl benzoates, C6H5CO2C6H4-X.

Conformations of Bridged Diphenyls. VI. Substituent Effects and Internal Rotation in Triply Ortho-substituted Diphenyl Ethers

1974 ◽  
Vol 52 (19) ◽  
pp. 3297-3302 ◽  
Author(s):  
Harm Benjamins ◽  
Fazal Haque Dar ◽  
W. David Chandler
Keyword(s):  
Free Energy ◽  
Experimental Evidence ◽  
Internal Rotation ◽  
Energy Barrier ◽  
Substituent Effects ◽  
Free Energy Barrier ◽  
Diphenyl Ethers ◽  
Ortho Substituent

Experimental evidence is presented to support the hypothesis that, in triply ortho-substituted diphenyl ethers, conformer interconversion involves both rings. The free energy barrier, measured by p.m.r., is sensitive to substituent effects arising in the ring having only one ortho substituent. The exceptionally high barrier found when an ortho iodine is present is consistent with the existence of a substituent-inside intermediate occurring during conformer conversion.

Ortho-substituent effects in polarography

1967 ◽  
Vol 89 (21) ◽  
pp. 5359-5362 ◽  
Author(s):  
William W. Hussey ◽  
A. James. Diefenderfer
Keyword(s):  
Substituent Effects ◽  
Ortho Substituent

How does organic structure determine organic reactivity? The effect of ortho-dimethyl groups on the nucleophilic substitution and alkene-forming elimination reactions of ring-substituted cumyl derivatives

1999 ◽  
Vol 77 (5-6) ◽  
pp. 922-933 ◽  
Author(s):  
Tina L Amyes ◽  
Tadeusz Mizerski ◽  
John P Richard
Keyword(s):  
Rate Constant ◽  
Nucleophilic Addition ◽  
Substituent Effects ◽  
Fold Increase ◽  
Methyl Groups ◽  
Diffusion Limited ◽  
Azide Ion ◽  
Brønsted Base ◽  
High Concentrations ◽  
Ortho Substituent

The addition of a pair of ortho-methyl groups to ring-substituted cumyl derivatives to give the corresponding 2,6-dimethylcumyl derivatives X-1-Y leads to modest (<5-fold) changes in the observed rate constant for reaction in 50:50 (v:v) trifluoroethanol-water (I = 0.50, NaClO4). The reactions of X-1-Y proceed by a stepwise mechanism through the liberated 2,6-dimethylcumyl carbocations X-2 that partition between nucleophilic addition of solvent and deprotonation to give good yields ([Formula: see text] 67%) of the corresponding 2-(2,6-dimethylaryl)propenes X-3. The carbocations X-2 are also trapped by nucleophilic addition of azide ion to give good yields ([Formula: see text] 68% at [N3-] = 0.50 M) of the corresponding 2,6-dimethylcumyl azides X-1-N3. In the presence of high concentrations of azide ion there are constant limiting yields of the alkenes X-3, which shows that X-2 also undergo significant reactions with azide ion as a Brønsted base. The product rate constant ratios for partitioning of the 2,4,6-trimethylcumyl carbocation Me-2 between reaction with azide ion as a Lewis and a Brønsted base, kaz/kB, the nucleophilic addition of azide ion and solvent, kaz/ks (M-1), and deprotonation by solvent, kaz/ke (M-1), were combined with (kaz + kB) = 5 × 109 M-1 s-1 for the diffusion-limited reaction of azide ion to give absolute rate constants for the reactions of Me-2. The data show that the addition of a pair of ortho-methyl groups to the 4-methylcumyl carbocation to give the sterically hindered Me-2 results in a 70-fold decrease in the rate constant for nucleophilic addition of solvent to the benzylic carbon, but a 60-fold increase in the rate constant for deprotonation of the carbocation by solvent.Key words: carbocation, ortho-substituent effects, steric effects, solvolysis, elimination.

scholarly journals Triazolium Salt Organocatalysis: Mechanistic Evaluation of Unusual Ortho-Substituent Effects on Deprotonation

Catalysts ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 1055
Author(s):  
Peter Quinn ◽  
Matthew S. Smith ◽  
Jiayun Zhu ◽  
David R. W. Hodgson ◽  
AnnMarie C. O’Donoghue
Keyword(s):  
Kinetic Data ◽  
Kinetic Method ◽  
Substituent Effects ◽  
Catalytic Efficiency ◽  
Heterocyclic Carbenes ◽  
Pyridyl Nitrogen ◽  
Conformational Preferences ◽  
Catalytic Mechanisms ◽  
Ortho Substituent ◽  
Triazolium Salts

Organocatalysis by N-heterocyclic carbenes is normally initiated by the deprotonation of precursor azolium ions to form active nucleophilic species. Substituent effects on deprotonation have an impact on catalytic efficiency and provide insight into general catalytic mechanisms by commonly used azolium systems. Using an NMR kinetic method for the analysis of C(3)-H/D exchange, we determined log kex–pD profiles for three ortho-substituted N-aryl triazolium salts, which enables a detailed analysis of ortho-substituent effects on deprotonation. This includes N-5-methoxypyrid-2-yl triazolium salt 7 and di-ortho-methoxy and di-ortho-isopropoxyphenyl triazolium salts 8 and 9, and we acquired additional kinetic data to supplement our previously published analysis of N-pyrid-2-yl triazolium salt 6. For 2-pyridyl triazoliums 6 and 7, novel acid catalysis of C(3)-H/D exchange is observed under acidic conditions. These kinetic data were supplemented by DFT analyses of the conformational preferences of 6 upon N-protonation. A C(3) deprotonation mechanism involving intramolecular general base deprotonation by the pyridyl nitrogen of the N(1)-deuterated dicationic triazolium salt is most consistent with the data. We also report kDO values (protofugalities) for deuteroxide-catalyzed exchange for 6–9. The protofugalities for 8 and 9 are the lowest values to date in the N-aryl triazolium series.

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