Thermal rearrangement of α,β- to β,γ-unsaturated esters. Evidence for a 1,5-hydrogen transfer mechanism

1968 ◽  
Vol 46 (13) ◽  
pp. 2225-2232 ◽  
Author(s):  
Donald E. McGreer ◽  
Norman W. K. Chiu
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Hydrogen Transfer ◽  
Activation Parameters ◽  
Transfer Mechanism ◽  
Thermal Rearrangement ◽  
Kcal Mole ◽  
Isopropyl Group ◽  
First Order ◽  
Group A ◽  
Entropy Of Activation

Methyl cis-4-methyl-2-pentenoate (1) has been found to rearrange at 252 °C by a simple first-order and presumably unimolecular mechanism to methyl 4-methyl-3-pentenoate (3) with a rate constant k of 4.28 × 10−5 s−1. The heat of activation ΔH†, was determined to be 37.5 ± 2 kcal/mole and the entropy of activation, ΔS†, was determined to be −8.2 ± 4 e.u. These activation parameters and the steric requirements of the reaction support a mechanism involving a cyclic 1,5-transfer of hydrogen. Studies on the isomerization of methyl cis-2-pentenoate, methyl cis-2,4-dimethyl-2-pentenoate, and methyl cis-2-methyl-2-pentenoate to the corresponding 3-pentenoates suggest that the 1,5-hydrogen transfer mechanism could well be general for the equilibration of α,β- and β,γ-unsaturated esters.An isopropyl group cis to a methyl or a carbomethoxy group on a double bond is shown by nuclear magnetic resonance to prefer a conformation with the methyls of the isopropyl group held away from the methyl or carbomethoxy group. A cis hydrogen does not restrict the conformation of the isopropyl group.

scholarly journals Cure Kinetics of an Optical Polythiourethane with Amine Catalyst by IR Analysis

2019 ◽  
Vol 2019 ◽  
pp. 1-10
Author(s):  
Weiping Du ◽  
Guiming Zhang ◽  
Song Wang ◽  
Lianjiang Tan ◽  
Huifang Chen
Keyword(s):  
Reaction Rate ◽  
Activation Parameters ◽  
Cure Kinetics ◽  
Order Kinetic ◽  
Cure Reaction ◽  
First Order ◽  
Entropy Of Activation ◽  
Catalyst Content ◽  
Ir Analysis ◽  
Kinetics Of

An optical polythiourethane based on m-xylylene diisocyanate (XDI) and 4-mercaptomethyl-3,6-dithia-1,8-octanedithiol (BES) has been studied. Triethylamine was adopted as a catalyst, and the solid-state isothermal cure reaction was carried out using FTIR spectroscopy, in the temperature range of 75°C-105°C. The -NCO absorption band of XDI was used to monitor the conversion of diisocyanate into polythiourethane. The reaction rate enhanced with an increase in the content of the catalyst, and the gel time determined by swelling test was shorter for the system with higher catalyst content. Kinetic parameters were calculated from the infrared spectrum data, and the results showed that the curing reaction of polythiourethane accords with first-order kinetic characteristics. The activation parameters obtained from the evaluation of kinetic data were △H∗=97.22 kJ mol−1, △S∗=−6.77 J K−1 mol−1, and Ea=100.23 kJ mol−1. The observed negative entropy of activation value supported the formation of a transition state in the cure reaction.

Applications of proton magnetic resonance to rotational isomerism in halotoluene derivatives. IV. α,α,2,4,6-Pentachlorotoluene in carbon disulfide, an exchanging ABC system

1970 ◽  
Vol 48 (24) ◽  
pp. 3877-3881 ◽  
Author(s):  
Helen G. Gyulai ◽  
B. J. Fuhr ◽  
H. M. Hutton ◽  
T. Schaefer
Keyword(s):  
Carbon Disulfide ◽  
Activation Parameters ◽  
Frequency Factor ◽  
Kcal Mole ◽  
Hindered Rotation ◽  
Line Shapes ◽  
Line Shape Analysis ◽  
Enthalpy Of Activation ◽  
Carbon Carbon Bond ◽  
Entropy Of Activation

The p.m.r. of α,α,2,4,6-pentachlorotoluene in carbon disulfide solution displays hindered rotation about the sp2–sp3 carbon–carbon bond, causing broadening and collapse of the proton resonance spectrum. A full line-shape analysis using the computer program DNMR gives an activation energy of 14.2 ± 0.3 kcal/mole, a frequency factor of 11.9 ± 0.2, an enthalpy of activation of 13.7 ± 0.3 kcal/mole, and an entropy of activation of −4.4 ± 1 e.u. These data are compared with the activation parameters obtained in methylcyclohexane and toluene-d8 solutions from different line shapes.

Activation parameters for the reconstitution of apotyrosinase by copper

1993 ◽  
Vol 71 (1-2) ◽  
pp. 96-98 ◽  
Author(s):  
Donald C. Wigfield ◽  
Douglas M. Goltz
Keyword(s):  
Rate Constants ◽  
Activation Parameters ◽  
Divalent Copper ◽  
First Order ◽  
Order Rate ◽  
Entropy Of Activation ◽  
Pseudo First Order ◽  
Fold Excess

The reaction of apotyrosinase with divalent copper to give enzymatically active tyrosinase has been studied at pH 8.2 and temperatures from 278 to 303 K. At a 10-fold excess of Cu(II) over enzyme, the pseudo-first order rate constants range from 1.32 × 10−3 s−1 to 2.93 × 10−2 s−1 and yield activation parameters of ΔH≠ = 85 ± 3 kJ∙mol−1 and ΔS≠ = 5 ± 20 J∙mol−1∙K−1. The near zero value for the entropy of activation is discussed.Key words: tyrosinase, copper.

CYCLOADDITIONS: X. KINETICS OF THE THERMAL DECARBONYLATION OF DICYCLOPENTADIENE-1.8-DIONE

1966 ◽  
Vol 44 (17) ◽  
pp. 2051-2056 ◽  
Author(s):  
John E. Baldwin
Keyword(s):  
Carbon Monoxide ◽  
Activation Parameters ◽  
Order Reaction ◽  
First Order Reaction ◽  
Kcal Mole ◽  
First Order ◽  
Kinetics Of ◽  
Thermal Decarbonylation

The thermal cycloelimination of carbon monoxide from dicyclopentadiene-1,8-dione is a kinetically well-behaved first-order reaction. At 380 °K the activation parameters for the process are ΔH≠ = 34.5 ± 0.8 kcal mole−1 and ΔS≠ = +9.8 ± 2.3 e.u. mole−1. Application of the theoretical proposals of Woodward and Hoffmann indicates that this necessarily disrotatory decarbonylation may be concerted.

Kinetics and Mechanism of Hexachloroiridate(IV) Oxidation of Arsenic(III) in Acidic Perchlorate Solutions

1992 ◽  
Vol 57 (7) ◽  
pp. 1451-1458 ◽  
Author(s):  
Refat M. Hassan
Keyword(s):  
Ionic Strength ◽  
Fractional Order ◽  
Activation Parameters ◽  
Order Reaction ◽  
First Order Reaction ◽  
Intermediate Complex ◽  
Constant Ionic Strength ◽  
Kinetics Of Oxidation ◽  
First Order ◽  
Kinetics Of

The kinetics of oxidation of arsenic(III) by hexachloroiridate(IV) at lower acid concentrations and at constant ionic strength of 1.0 mol dm-3 have been investigated spectrophotometrically. A first-order reaction in [IrCl62-] and fractional order with respect to arsenic(III) have been observed. A kinetic evidence for the formation of an intermediate complex between the hydrolyzed arsenic(III) species and the oxidant was presented. The results showed that decreasing the [H+] is accompanied by an appreciable acceleration of the rate of oxidation. The activation parameters have been evaluated and a mechanism consistent with the kinetic results was suggested.

Kinetic Studies of [4n+2]π-Thermal Cyclodimerization of 1-(3-Pyridazinyl)-3-oxidopyridinium Betaines

1992 ◽  
Vol 57 (9) ◽  
pp. 1951-1959 ◽  
Author(s):  
Madlene L. Iskander ◽  
Samia A. El-Abbady ◽  
Alyaa A. Shalaby ◽  
Ahmed H. Moustafa
Keyword(s):  
Energy Gap ◽  
Activation Parameters ◽  
Kinetic Studies ◽  
Cyclic Transition ◽  
Concerted Mechanism ◽  
First Order ◽  
Thermodynamic Activation Parameters ◽  
Cyclic Transition State ◽  
Complete Dissociation ◽  
Homo Lumo

The reactivity of the base induced cyclodimerization of 1-(6-arylpyridazin-3-yl)-3-oxidopyridinium chlorides in a pericyclic process have been investigated kinetically at λ 380 nm. The reaction was found to be second order with respect to the liberated betaine and zero order with respect to the base. On the other hand dedimerization (monomer formation) was found to be first order. It was shown that dimerization is favoured at low temperature, whereas dedimerization process is favoured at relatively high temperature (ca 70 °C). Solvent effects on the reaction rate have been found to follow the order ethanol > chloroform ≈ 1,2-dichloroethane. Complete dissociation was accomplished only in 1,2-dichloroethane at ca 70 °C. The thermodynamic activation parameters have been calculated by a standard method. Thus, ∆G# has been found to be independent on substituents and solvents. The high negative values of ∆S# supports the cyclic transition state which is in favour with the concerted mechanism. MO calculations using SCF-PPP approximation method indicated low HOMO-LUMO energy gap of the investigated betaines.

Vulcanization of Elastomers. 23. The Chemical Kinetics of Vulcanization Reactions and The Physical Properties of The Vulcanizates. I

1960 ◽  
Vol 33 (2) ◽  
pp. 335-341
Author(s):  
Walter Scheele ◽  
Karl-Heinz Hillmer
Keyword(s):  
Activation Energy ◽  
Physical Properties ◽  
Chemical Kinetics ◽  
Kcal Mole ◽  
First Order ◽  
Equilibrium Swelling ◽  
Kinetics Of ◽  
Kinetics Of Vulcanization ◽  
Limiting Value ◽  
Good Agreement

Abstract As a complement to earlier investigations, and in order to examine more closely the connection between the chemical kinetics and the changes with vulcanization time of the physical properties in the case of vulcanization reactions, we used thiuram vulcanizations as an example, and concerned ourselves with the dependence of stress values (moduli) at different degrees of elongation and different vulcanization temperatures. We found: 1. Stress values attain a limiting value, dependent on the degree of elongation, but independent of the vulcanization temperature at constant elongation. 2. The rise in stress values with the vulcanization time is characterized by an initial delay, which, however, is practically nonexistent at higher temperatures. 3. The kinetics of the increase in stress values with vulcanization time are both qualitatively and quantitatively in accord with the dependence of the reciprocal equilibrium swelling on the vulcanization time; both processes, after a retardation, go according to the first order law and at the same rate. 4. From the temperature dependence of the rate constants of reciprocal equilibrium swelling, as well as of the increase in stress, an activation energy of 22 kcal/mole can be calculated, in good agreement with the activation energy of dithiocarbamate formation in thiuram vulcanizations.

Mikrowellenspektrum und Struktur von Fluortribromsilan und Methyltribromsilan

1968 ◽  
Vol 23 (11) ◽  
pp. 1819-1821 ◽  
Author(s):  
M. Mitzlaff ◽  
R. Holm ◽  
H. Hartmann
Keyword(s):  
Least Squares ◽  
Internal Rotation ◽  
Kcal Mole ◽  
Rotational Constants ◽  
Methyl Group ◽  
Microwave Spectra ◽  
Group A

The microwave spectra of SiFBr3 and CH3SiBr have been investigated in the region from 30 to 40 GHz. Assuming reasonable values for dSi-F, dSi-C and the methyl group a least squares analysis of the rotational constants yieldsdSi-Br ≮Br—Si—BrSiFBr3 (2,171 ± 0,001) A (111,36 ± 0,15)°,CH3SiBr3 (2,175±0,001) A (111,09±0,15)°.A barrier to internal rotation of about 1 kcal/mole is estimated by the intensity method.

scholarly journals Poly(N-isopropylacrylamide-co-methacrylic acid) microgel stabilized copper nanoparticles for catalytic reduction of nitrobenzene

2015 ◽  
Vol 33 (3) ◽  
pp. 627-634 ◽  
Author(s):  
Zahoor H. Farooqi ◽  
Zonarah Butt ◽  
Robina Begum ◽  
Shanza Rhauf Khan ◽  
Ahsan Sharif ◽  
...  
Keyword(s):  
Copper Nanoparticles ◽  
Methacrylic Acid ◽  
Catalytic Reduction ◽  
Aqueous Media ◽  
Activation Parameters ◽  
Reducing Agent ◽  
Different Temperatures ◽  
Entropy Of Activation ◽  
Micro Reactors

Abstract Poly(N-isopropylacrylamide-co-methacrylic acid) microgels [p(NIPAM-co-MAAc)] were synthesized by precipitation polymerization of N-isopropylacrylamide and methacrylic acid in aqueous medium. These microgels were characterized by dynamic light scattering and Fourier transform infrared spectroscopy. These microgels were used as micro-reactors for in situ synthesis of copper nanoparticles using sodium borohydride (NaBH4) as reducing agent. The hybrid microgels were used as catalysts for the reduction of nitrobenzene in aqueous media. The reaction was performed with different concentrations of cat­alyst and reducing agent. A linear relationship was found between apparent rate constant (kapp) and amount of catalyst. When the amount of catalyst was increased from 0.13 to 0.76 mg/mL then kapp was increased from 0.03 to 0.14 min-1. Activation parameters were also determined by performing reaction at two different temperatures. The catalytic process has been discussed in terms of energy of activation, enthalpy of activation and entropy of activation. The synthesized particles were found to be stable even after 14 weeks and showed catalytic activity for the reduction of nitrobenzene.

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