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.

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

scholarly journals Rate and Product Studies with 1-Adamantyl Chlorothioformate under Solvolytic Conditions

2021 ◽  
Vol 22 (14) ◽  
pp. 7394
Author(s):  
Kyoung Ho Park ◽  
Mi Hye Seong ◽  
Jin Burm Kyong ◽  
Dennis N. Kevill
Keyword(s):  
Rate Constants ◽  
Isotope Effects ◽  
Ion Pairs ◽  
Carbonyl Sulfide ◽  
Activation Parameters ◽  
Chloride Ions ◽  
Reaction Channels ◽  
Decomposition Pathway ◽  
Solvent Isotope ◽  
Solvent Isotope Effects

A study was carried out on the solvolysis of 1-adamantyl chlorothioformate (1-AdSCOCl, 1) in hydroxylic solvents. The rate constants of the solvolysis of 1 were well correlated using the Grunwald–Winstein equation in all of the 20 solvents (R = 0.985). The solvolyses of 1 were analyzed as the following two competing reactions: the solvolysis ionization pathway through the intermediate (1-AdSCO)+ (carboxylium ion) stabilized by the loss of chloride ions due to nucleophilic solvation and the solvolysis–decomposition pathway through the intermediate 1-Ad+Cl− ion pairs (carbocation) with the loss of carbonyl sulfide. In addition, the rate constants (kexp) for the solvolysis of 1 were separated into k1-Ad+Cl− and k1-AdSCO+Cl− through a product study and applied to the Grunwald–Winstein equation to obtain the sensitivity (m-value) to change in solvent ionizing power. For binary hydroxylic solvents, the selectivities (S) for the formation of solvolysis products were very similar to those of the 1-adamantyl derivatives discussed previously. The kinetic solvent isotope effects (KSIEs), salt effects and activation parameters for the solvolyses of 1 were also determined. These observations are compared with those previously reported for the solvolyses of 1-adamantyl chloroformate (1-AdOCOCl, 2). The reasons for change in reaction channels are discussed in terms of the gas-phase stabilities of acylium ions calculated using Gaussian 03.

Isotope effects and activation parameters for the proton transfer reaction from 1-(4-nitrophenyl)-1-nitroethane to free anions and ion pairs of cesium n-propoxide in n-propanol solvent

1986 ◽  
Vol 64 (6) ◽  
pp. 1021-1025 ◽  
Author(s):  
Arnold Jarczewski ◽  
Grzegorz Schroeder ◽  
Przemyslaw Pruszynski ◽  
Kenneth T. Leffek
Keyword(s):  
Proton Transfer ◽  
Rate Constants ◽  
Isotope Effects ◽  
Ion Pairs ◽  
Activation Parameters ◽  
Solvation Shell ◽  
Ion Pair ◽  
Initial State ◽  
Free Ion ◽  
Deuteron Transfer

Rate constants for the proton and deuteron transfer from 1-(4-nitrophenyl)-1-nitroethane to cesium n-propoxide in n-propanol have been measured under pseudo-first-order conditions with an excess of base for four temperatures between 5 and 35 °C. Using literature values of the fraction of cesium n-propoxide ion pairs that are dissociated into free ions, separate second-order rate constants for the proton and deuteron transfer to the ion pair and to the free ion have been calculated. The cesium n-propoxide ion pair is about 2.8 times more reactive than the free n-propoxide ion. The primary kinetic isotope effects for the two reactions are the same (kH/kD = 6.1–6.3 at 25 °C) within experimental error. The enthalpy of activation is smaller for the ion-pair reaction and the entropy of activation more negative than for the free-ion reaction. For proton transfer, ΔH±ion pair = 8.3 ± 0.2 kcal mol−1, ΔH±ion = 9.6 ± 1.0 kcal mol−1, ΔS±ion pair = −12.3 ± 0.6 cal mol−1 deg−1, ΔS±ion = −10.1 ± 3.4 cal mol−1 deg−1. The greater reactivity of the ion pair relative to the free ion is interpreted in terms of the weaker solvation shell of the ion pair in the initial state.

Laser flash photolysis studies of the formation and reactivities of phenyl(naphthyl)methyl carbocations generated from phosphonium salt precursors

1992 ◽  
Vol 70 (6) ◽  
pp. 1784-1794 ◽  
Author(s):  
E. O. Alonso ◽  
L. J. Johnston ◽  
J. C. Scaiano ◽  
V. G. Toscano
Keyword(s):  
Rate Constants ◽  
Phosphonium Salt ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Ion Pairs ◽  
Laser Flash ◽  
Product Formation ◽  
Quantum Yields ◽  
Back Reaction ◽  
Transient Experiments

The photolysis of several substituted phenyl(naphthyl)methyl triphenylphosphonium chlorides has been examined using a combination of laser flash photolysis experiments and product studies. Both carbocation and radical intermediates have been characterized in the transient experiments, with the relative yields depending strongly on the solvent. For example, in alcohols, acetonitrile, or aqueous solvents cation formation predominates while acetonitrile/dioxane mixtures (5–10%) are required for the observation of radicals. Quantum yields for cation formation vary from 0.79 in methanol to 0.093 in 1:4 acetonitrile/dioxane, as measured by product studies and transient experiments, respectively. The addition of perchlorate salts leads to dramatic enhancements in the cation lifetimes; the effects are particularly pronounced for acetonitrile/dioxane mixtures where the cation yields also increase by factors of 3–4. In this case the effects are attributed primarily to replacement of chloride by perchlorate in the initial ion pairs. The combined data from both solvent and perchlorate salt effects on the cation lifetimes and yields suggest that the excited state of the phosphonium salt cleaves homolytically, followed by electron transfer within the initial radical/triphenylphosphine radical cation pair to generate carbocation, as opposed to direct heterolytic cleavage. The cation yields also indicate that back reaction to regenerate starting material, as well as product formation within the initial geminate cage, occur in some solvents. The effects of solvent and added perchlorate salts on the rate constants for reaction with nucleophiles have been examined. For example, rate constants that vary by an order of magnitude have been measured for quenching by azide ion in various aqueous acetonitrile and trifluoroethanol mixtures.

The Synthesis of Imidazo[1,2-f]phenanthridines, Phenanthro-[9,10-d]imidazoles, and Phenanthro[9′,10′:4,5]imidazo[1,2-f]-phenanthridines via Intramolecular Oxidative Aromatic Coupling

Synthesis ◽  
2017 ◽  
Vol 49 (20) ◽  
pp. 4651-4662 ◽  
Author(s):  
Kamil Skonieczny ◽  
Jarosław Jaźwiński ◽  
Daniel Gryko
Keyword(s):  
Blue Emission ◽  
Coupling Reaction ◽  
Quantum Yields ◽  
Unsaturated Ketone ◽  
Oxidative Coupling Reaction ◽  
Fluorescence Quantum Yields ◽  
Efficient Access ◽  
Close Proximity ◽  
Electron Donating Groups ◽  
Derivatives Of

A short and efficient access to phenanthro[9,10-d]imidazoles, imidazo[1,2-f]phenanthridines, and phenanthro[9′,10′:4,5]imidazo[1,2-f]phenanthridines was achieved by the action of [bis(trifluoroacetoxy)iodo]benzene (PIFA) on properly substituted tetraaryl­-imidazoles. By pre-installing suitable electron-donating groups, it is possible to control the site of intramolecular oxidative aromatic coupling. In particular, by placing 3,4-dimethoxyphenyl and 3-methoxyphenyl moieties in close proximity, it was possible to direct the reaction into forming two biaryl linkages leading eventually to the formation of phenanthro[9′,10′:4,5]imidazo[1,2-f]phenanthridines. Starting from bis-aldehydes that are derivatives of thieno[3,2-b]thiophene and fluorene enabled the synthesis of π-expanded imidazoles bearing 8-9 conjugated rings. By placing a dimethoxynaphthalene unit on the imidazole scaffold, we have directed the oxidative coupling reaction towards closing a five-membered ring with concomitant removal of methoxy group leading to formation of an α,β-unsaturated ketone. All resulting π-expanded imidazoles display blue emission, and the fluorescence quantum yields in some cases reaches 0.9.

The structure, photochemical reactivity, and photophysical properties of adamantyl X-substituted aryl ethers and a comparison with the alkyl groups, methyl, tert-butyl, and allyl

2005 ◽  
Vol 83 (9) ◽  
pp. 1237-1252 ◽  
Author(s):  
A L Pincock ◽  
J A Pincock
Keyword(s):  
Excited State ◽  
Rate Constants ◽  
Singlet State ◽  
Bond Cleavage ◽  
Photophysical Properties ◽  
Excited Singlet State ◽  
Quantum Yields ◽  
Aryl Ether ◽  
Excited Singlet ◽  
Aryl Ethers

The structure, photophysical properties, and photochemistry of the adamantyl aryl ethers 1 in both methanol and cyclohexane have been examined. UV absorption spectra, 13C NMR chemical shifts, X-ray structures, and Gaussian calculations (B3LYP/6-31G(d)) indicate that these ethers adopt a 90° conformer in the ground state. In contrast, fluorescence spectra, excited singlet state lifetimes, and calculations (TDDFT) indicated a 0° conformer is preferred in the first excited singlet state S1. Irradiation in either solvent results in the formation of adamantane and the corresponding phenol as the major products, both derived from radical intermediates generated by homolytic cleavage of the ether bond. The 4-cyano substituted ether 1j was the only one to form the ion-derived product, 1-methoxyadamantane (16% yield), on irradiation in methanol. Rate constants of bond cleavage for these ethers from S1 were estimated by two different methods by comparison with the unreactive anisoles 2, but the effect of substituents was too small to determine structure–reactivity correlations. The temperature dependence of the quantum yields of the fluorescence of the unsub stituted, 4-methoxy and 4-cyano derivatives of 1 and 2 were also determined. These results indicated that the activated process for 1 was mainly bond cleavage for the 4-cyano substrate whereas for 2, it was internal conversion and intersystem crossing. Key words: aryl ether photochemistry, fluorescence, excited-state rate constants, excited-state temperature effects.

Ion Pairing and the Reaction of Alkali Metal Ferrocyanides and Persulfates

1971 ◽  
Vol 49 (18) ◽  
pp. 2943-2947 ◽  
Author(s):  
R. W. Chlebek ◽  
M.W. Lister
Keyword(s):  
Alkali Metal ◽  
Rate Constants ◽  
Equilibrium Constants ◽  
Ion Pairs ◽  
Activation Parameters ◽  
Ion Pairing ◽  
Similar Rate ◽  
Thermodynamic Quantities ◽  
Kinetics Of

Osmometric measurements have been made on the alkali metal persulfates, and these are interpreted in terms of formation of ion pairs, MS2O8−, by means of the method of Masterton and Berka (5). Equilibrium constants, and the derived thermodynamic quantities are deduced for the reactions [Formula: see text]. These results are applied to the interpretation of the kinetics of the reactions[Formula: see text]With M = K+, Rb+, and Cs+, the reacting species are MFe(CN)63− + MS2O8−, with very similar rate constants; with M = Li+, Na+ the species are MFe(CN)63− + S2O82−; and for lithium the reaction of Fe(CN)64− + S2O82− is also important. Rate constants and activation parameters are deduced.

Understanding the reversible anodic behaviour and fluorescence properties of fluorenylazomethines — A structure–property study

2010 ◽  
Vol 88 (9) ◽  
pp. 945-953 ◽  
Author(s):  
Satyananda Barik ◽  
Sayuri Friedland ◽  
W. G. Skene
Keyword(s):  
Low Temperature ◽  
Radical Cation ◽  
Oxidation Potential ◽  
Quantum Yields ◽  
Structure Property ◽  
Model Compounds ◽  
Fluorescence Quantum Yields ◽  
Anodic Behaviour ◽  
Electronic Groups ◽  
Electron Donating Groups

A series of fluorenylazomethine dyads and triads were prepared by simple condensation between the corresponding amine and aldehyde fluorene derivatives. These compounds were prepared as model compounds for investigating the effects of substitution and electronic groups on both the electrochemical properties and fluorescence quantum yields. It was found that the oxidation potential could be decreased by both incorporating electron donating groups and increasing the degree of conjugation. It was further found that alkylation in the fluorene’s 9-position increased the azomethine degree of conjugation by forcing all the fluorene moieties to be coplanar with the azomethine bonds to which they are attached. Meanwhile, reversible radical cation behaviour was possible by substituting the terminal 2,2′-positions with atoms other than hydrogen. The radical cation was theoretically found to be distributed evenly across the fluorene, corroborating the reversible anodic behaviour with 2,2′-substitution. The fluorescence quantum yields of the azomethines were not found to be dependent on substitution. This was because the azomethine fluorescence was found to be quenched relative to their precursors regardless of substitution. The fluorescence could be restored at both low temperature and by acid protonation.

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