Substituent Effects on the Rate Constants for the Photo-Claisen Rearrangement of Allyl Aryl Ethers

2002 ◽  
Vol 124 (33) ◽  
pp. 9768-9778 ◽  
Author(s):  
Alexandra L. Pincock ◽  
James A. Pincock ◽  
Roumiana Stefanova
Keyword(s):  
Rate Constants ◽  
Claisen Rearrangement ◽  
Substituent Effects ◽  
Aryl Ethers

Substituent effects, Arrhenius activation parameters, and rate constants for the photo–Claisen rearrangement of allyl aryl ethers

2008 ◽  
Vol 86 (7) ◽  
pp. 686-690 ◽  
Author(s):  
Carlos M Gonzalez ◽  
James A Pincock
Keyword(s):  
Rate Constants ◽  
Claisen Rearrangement ◽  
Ion Pairs ◽  
Substituent Effects ◽  
Activation Parameters ◽  
Quantum Yields ◽  
Intermediate Radical ◽  
Fluorescence Quantum Yields ◽  
Aryl Ethers ◽  
Electron Donating Groups

The temperature-dependence of fluorescence quantum yields in both methanol and methylcyclohexane has been used to obtain the rate constants of reaction for the activated process that converts the singlet excited state S1 of a set of ring-substituted aryl allyl ethers to an intermediate radical pair in the photo–Claisen rearrangement. These rate constants are correlated with the O–H bond dissociation energy of the corresponding ring-substituted phenols; that is, electron-donating groups (CH3, OCH3) accelerate the reaction relative to electron-withdrawing groups (CF3, CN). The rate constants obtained span two orders of magnitude, from 5.4 × 107 s–1 for X = 3–CN to 800 × 107 s–1 for X = 4–OCH3, in methylcylcohexane. Moreover, the rate constants are similar in the two solvents, methanol and methcyclohexane, indicating that radical pairs, not ion pairs, are the reactive intermediates, as expected on the basis of previous mechanistic proposals for the photo–Claisen rearrangement. Finally, the rate constants obtained by this temperature-dependent method are in good agreement with those previously reported from a method using the corresponding unreactive anisoles as a model.Key words: allyl aryl ethers, photo–Claisen rearrangement, substituent effects, activation parameters.

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.

Kinetic Study of Hydrolysis of Benzoates. Part XXVI. Variation of the Substituent Effect with Solvent in Alkaline Hydrolysis of Substituted Alkyl Benzoates

2006 ◽  
Vol 71 (11-12) ◽  
pp. 1557-1570 ◽  
Author(s):  
Vilve Nummert ◽  
Mare Piirsalu ◽  
Ilmar A. Koppel
Keyword(s):  
Kinetic Study ◽  
Alkaline Hydrolysis ◽  
Rate Constants ◽  
Substituent Effect ◽  
Substituent Effects ◽  
Alkyl Substituent ◽  
Solvent Parameters ◽  
Substituent Constants ◽  
Hydrolysis Of ◽  
Main Factor

The second-order rate constants k2 (dm3 mol-1 s-1) for the alkaline hydrolysis of substituted alkyl benzoates C6H5CO2R have been measured spectrophotometrically in aqueous 0.5 M Bu4NBr at 50 and 25 °C (R = CH3, CH2Cl, CH2CN, CH2C≡CH, CH2C6H5, CH2CH2Cl, CH2CH2OCH3, CH2CH3) and in aqueous 5.3 M NaClO4 at 25 °C (R = CH3, CH2Cl, CH2CN, CH2C≡CH). The dependence of the alkyl substituent effects on different solvent parameters was studied using the following equations:      ∆ log k = c0 + c1σI + c2EsB + c3∆E + c4∆Y + c5∆P + c6∆EσI + c7∆YσI + c8∆PσI     ∆ log k = c0 + c1σ* + c2EsB + c3∆E + c4∆Y + c5∆P + c6∆Eσ* + c7∆Yσ* + c8∆Pσ* .  ∆ log k = log kR - log kCH3. σI and σ* are the Taft inductive and polar substituent constants. E, Y and P are the solvent electrophilicity, polarity and polarizability parameters, respectively. In the data treatment ∆E = ES - EH2O , ∆Y = YS - YH2O , ∆P = PS - PH2O were used. The solvent electrophilicity, E, was found to be the main factor responsible for changes in alkyl substituent effects with medium. When σI constants were used, variation of the polar term of alkyl substituents with the solvent electrophilicity E was found to be similar to that observed earlier for meta and para substituents, but twice less when σ* constants were used. The steric term for alkyl substituents was approximately independent of the solvent parameters.

Investigating the microwave-accelerated Claisen rearrangement of allyl aryl ethers: Scope of the catalysts, solvents, temperatures, and substrates

2020 ◽  
Vol 61 (24) ◽  
pp. 151995
Author(s):  
Zi Hui ◽  
Songwei Jiang ◽  
Xiang Qi ◽  
Xiang-Yang Ye ◽  
Tian Xie
Keyword(s):  
Claisen Rearrangement ◽  
Aryl Ethers

Substituent effects of rate constants for thermal [4π + 2π] cycloreversion of spiro-fused β-lactam oxadiazolines

1993 ◽  
Vol 71 (6) ◽  
pp. 907-911 ◽  
Author(s):  
Michel Zoghbi ◽  
John Warkentin
Keyword(s):  
Thermal Decomposition ◽  
Rate Constant ◽  
Rate Constants ◽  
Transition States ◽  
Substituent Effects ◽  
Ground States ◽  
Phenyl Substituent ◽  
First Order ◽  
Average Value ◽  
Carbonyl Ylide

Twelve Δ3-1,3,4-oxadiazolines in which C-2 is also C-4 of a β-lactam moiety (spiro-fused β-lactam oxadiazoline system) were thermolyzed as solutions in benzene. Substituents in the β-lactam portion affect the rate constant for thermal decomposition of the oxadiazolines to N2, acetone, and a β-lactam-4-ylidene. The total spread of first-order rate constants at 100 °C was 47-fold and the average value was 6.7 × 10−4 s−1. A phenyl substituent at N-1 or at C-3 was found to be rate enhancing, relative to methyl. At C-3, H and Cl were also rate enhancing, relative to methyl. The data are interpreted in terms of the differential effects of substituents on the stabilities of the ground states, and on the stabilities of corresponding transition states for concerted, suprafacial, [4π + 2π] cycloreversion. The first products, presumably formed irreversibly, are N2 and a carbonyl ylide. The latter subsequently fragments to form acetone (quantitative) and a β-lactam-4-ylidene.

Substituent effects on rates of formation of methoxy-substituted carbonyl ylides from 2-aryl-2-methoxy- and 5-aryl-2-methoxy-Δ3-1,3,4-oxadiazolines

1984 ◽  
Vol 62 (8) ◽  
pp. 1646-1652 ◽  
Author(s):  
Michel Békhazi ◽  
Peter J. Smith ◽  
John Warkentin
Keyword(s):  
Transition State ◽  
Electron Density ◽  
Rate Constants ◽  
Substituent Effects ◽  
Partial Identification ◽  
Trans Isomers ◽  
First Order Kinetics ◽  
Bond Scission ◽  
Carbonyl Ylide ◽  
Substituent Constants

2-Aryl-2-methoxy-5,5-dimethyl-Δ3-1,3,4-oxadiazolines (4) and 5-aryl-2-methoxy-2,5-dimethyl-Δ3-1,3,4-oxadiazolines (5) were synthesized. Compounds 4 decompose in solution with first order kinetics. Rate constants are correlated with Hammett substituent constants (σ−) with ρ(49.2 °C) = 0.74 and 0.89 for CCl4, and CD3OD, respectively. The final products from 4 indicate that thermolysis involves the cleavage of both C—N bonds, to form N2 and, initially, a carbonyl ylide. Compounds 5, which were obtained as mixtures of cis/trans isomers containing several impurities, and which therefore gave poorer kinetic data, decomposed in CDCl3 solution with [Formula: see text] Carbonyl ylide intermediates, similar to those from the closelyrelated compounds 4, were assumed on the basis of analogy and on the basis of partial identification of products. The effects of para substituents in the aryl groups of 4 and 5 show that the transition states have greater electron density at C-2 of 4 and at C-5 of 5 than do the starting materials. In spite of the increase in electron density at C-2 of 4, the transition state must be less polar, overall, than the ground state because rate constants for thermolysis of 4 in methanol are smaller than those for CCl4, solvent. A plausible explanation for the substituent effects and the solvent effects is that the loss of N2 is concerted, with a transition state resembling more closely a spin paired 1,3-diradical than a 1,3-dipole. Alternative stepwise mechanisms, in which C2—N3 bond scission of 4 and C5—N4 bond scission of 5 are the rate-determining steps, leading to 1,5-diradical intermediates, can not be excluded on the basis of the evidence.

Substituent Effects on the Hydrolysis of p-Substituted Benzonitriles in Sulfuric Acid Solutions at (25.0± 0.1) °C

2008 ◽  
Vol 63 (9) ◽  
pp. 603-608 ◽  
Author(s):  
Khamis A. Abbas
Keyword(s):  
Sulfuric Acid ◽  
Rate Constants ◽  
Inductive Effect ◽  
Substituent Effects ◽  
Acid Solutions ◽  
Rate Determining Step ◽  
Inductive Effects ◽  
High Concentrations ◽  
Sulfuric Acid Solutions ◽  
Hydrolysis Of

The rate constants of the hydrolysis of p-substituted benzonitriles with sulfuric acid solutions (18.2 M to 10 M) have been determined spectrophotometrically at (25.1±0.1) °C. It was found that the catalytic activity of sulfuric acid was strongly inhibited by water. The logarithms of the observed rate constants were correlated with different substituent inductive (localized) and resonance (delocalized) constants. The results of the correlation studies indicated that the rate-determining step of the hydrolysis of benzonitriles in 18.2 M sulfuric acid was the addition of a nucleophile, and the hydrolysis was clearly enhanced by the electron-withdrawing inductive effect, while the rate-determining step of the hydrolysis of p-substituted benzonitriles in 10.0 M sulfuric acid was most probably the protonation of benzonitriles, and the rate constants increased by both electron-donating resonance and inductive effects. A mixture of the two mechanisms most probably occurred in 15.3 to 17.0 M sulfuric acid. HSO4 − rather thanwater most probably acted as nucleophile in the hydrolysis of benzonitriles especially at high concentrations of sulfuric acid solutions.

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