Reactions of methyl-substituted Hex-5-enyl and Pent-4-enyl radicals

1983 ◽  
Vol 36 (3) ◽  
pp. 545 ◽  
Author(s):  
ALJ Beckwith ◽  
CJ Easton ◽  
T Lawrence ◽  
AK Serelis
Keyword(s):  
Activation Energy ◽  
Kinetic Data ◽  
Ring Closure ◽  
Cyclic Transition ◽  
Transition Complexes

Relative and absolute kinetic data have been determined for ring closure of methyl-substituted hex-5-enyl radicals: 2-methyl- (10a), 3-methyl-(4a), 4-methyl-(5a), 2,2-dimethyl-(10c), 3,3-dimethyl-(4c) and 4,4-dimethyl-hex-5-enyl (5c) radicals, generated by interaction of tributylstannane with the corresponding bromides (1a)-(3a) and (1c)-(3c). Each radical undergoes regiospecific or highly regioselective 1,5-cyclization more rapidly than does the unsubstituted radical (4d). The rate enhancements, which arise mainly from lowering of the activation energy, can be rationalized in terms of the gem-dimethyl effect. 1,5-Ring closures of monosubstituted species are stereoselective: 2-methyl- and 4-methyl-hex-5-enyl radicals (10a) and (5a) give mainly trans products, whereas 3-methylhex-4- enyl radical gives mainly the cis. This behaviour reflects the effect of the substituent on the stabilities of cyclic transition complexes in chair-like conformations. Ring closure of 2,2-dimethylpent-4-enyl radical or of 3,3-dimethylpent-4-enyl radical (19) could not be detected.

A Theoretical and Experimental Investigation of the Kinetics of Ring Closure of the 3-Methyl-3-azahex-5-enyl Radical

1995 ◽  
Vol 48 (12) ◽  
pp. 2047 ◽  
Author(s):  
EW Della ◽  
AM Knill
Keyword(s):  
Activation Energy ◽  
Experimental Investigation ◽  
Force Field ◽  
Activation Barrier ◽  
Ring Closure ◽  
Force Field Calculations ◽  
Arrhenius Parameters ◽  
A Value ◽  
Kinetics Of

Evaluation of the Arrhenius parameters for ring closure of the 3-methyl-3-azahex-5-enyl radical is reported. Cyclization of the radical is found to occur with high regioselectivity giving the exo -trig product exclusively with an activation energy of 22 kJ mol-1 and log A value of 11.1. The experimental activation barrier compares favourably with that determined by force field calculations which predict a value of 21 kJ mol-1. The 3-methyl-3-azahex-5-enyl radical is therefore found to undergo ring closure some 70 times faster than the parent hex-5-enyl radical, in accord with predictions based upon geometrical considerations.

The adsorption of ethylene on silver(I) oxide. I. Rates of adsorption

1967 ◽  
Vol 20 (3) ◽  
pp. 399
Author(s):  
JA Allen ◽  
PH Scaife
Keyword(s):  
Activation Energy ◽  
Kinetic Data ◽  
Qualitative Explanation ◽  
Kcal Mole ◽  
Temperature Range ◽  
Elovich Equation

The rates of adsorption of ethylene on silver(I) oxide, Ag2O, have been measured in the temperature range 273-313�K. The kinetic data are analysed in terms of the generalized Elovich equation by methods developed and described in a previous paper.1 The activation energy derived from the rates at zero coverage is 15.6 kcal mole-1. The presence of isothermal anomalies is noted and the extent of each kinetic stage defined. A qualitative explanation of the existence of these stages is suggested.

scholarly journals Computer-Aided Arrhenius-Evaluation of Kinetic Data

1995 ◽  
Vol 50 (6) ◽  
pp. 549-554
Author(s):  
P. Hugo ◽  
J. Leonhardt ◽  
S. Wagner
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Kinetic Data ◽  
Evaluation Method ◽  
Arrhenius Law ◽  
Temperature Dependent ◽  
Dependent Part ◽  
Computer Aided ◽  
Temperature Programmed ◽  
Temperature Dependance

Abstract A new evaluation method is presented to analyse the temperature dependance of reactions with rates that can be separated into a temperature dependent and a concentration dependent part. The proposed method allows to evaluate isothermal, adiabatic, isoperibolic and temperature programmed measurements in an unified manner. To determine the activation energy an Arrhenius law but no explicite kinetic model has to be assumed. The application of the method is demonstrated using experimental data of different reactions from former investigations.

Kinetics of Rapid Thermal Oxidation of Silicon

1987 ◽  
Vol 92 ◽  
Author(s):  
Stephan E. Lassig ◽  
Thomas J. Debolske ◽  
John L. Crowley
Keyword(s):  
Activation Energy ◽  
Thermal Oxidation ◽  
Kinetic Data ◽  
Halogen Lamp ◽  
Heating Source ◽  
Rapid Thermal Oxidation ◽  
Set Up ◽  
Lamp Source ◽  
Kinetics Of ◽  
Tungsten Halogen Lamp

ABSTRACTThis paper presents kinetic data for the rapid thermal oxidation (RTO) of <100 silicon using a wall stabilized low pressure arc lamp as the heating source. The data shows a single activation energy of 1.31 eV over the temperature range of 900°C to 1200°C and times of 60 seconds to 240 seconds. Comparisons are made with published kinetic data of RTO using tungsten-halogen lamp source [1] and with furnace oxidation kinetics for short times (<240 sec.) [2]. “Wet” oxidation results using O2:H2 as the oxidizing ambient reveal a lower activation energy and preexponential coefficient than the dry oxidation. Also presented are results using an experimental set-up which exhibits ultraviolet enhanced oxidation.

scholarly journals Activation Energy Determination in Case of Independent Complex Kinetic Processes

Processes ◽  
2019 ◽  
Vol 7 (10) ◽  
pp. 738 ◽  
Author(s):  
Luciano ◽  
Svoboda
Keyword(s):  
Activation Energy ◽  
Kinetic Data ◽  
Kinetic Curve ◽  
Real Life ◽  
Isoconversional Methods ◽  
Heating Rates ◽  
Complex Process ◽  
Inflection Points ◽  
Kinetic Processes ◽  
Energy Determination

Theoretically simulated kinetic data were used to evaluate the performance of the most common isoconversional methods of kinetic analysis in complex-process scenarios with two independent overlapping processes exhibiting nucleation-growth kinetics, and further expand the conclusions for the autocatalytic kinetic processes with positive asymmetry. In close-to-real-life situations all the integral isoconversional methods provided practically indistinguishable E-α outcomes. The Friedman and incremental modified Vyazovkin methods results in significant over- and undershoots. However, the combined utilization of the integral and differential isoconversional methods was demonstrated to greatly contribute to the interpretation of the E-α dependences and estimation of E1 and E2—the conceptual evaluation involving positions of inflection points and plateaus is introduced. The influence of the range of applied heating rates q+ on the course of E-α dependences was studied. In this regard, the performance of the isoconversional methods changes significantly with both, the consistence of the shape of the complex kinetic curve and weighted presence of full overlaps of the involved sub-processes.

Ab initio study on the thermal decarboxylation of but-3-enoic acid and its derivatives

1994 ◽  
Vol 72 (5) ◽  
pp. 1338-1346 ◽  
Author(s):  
Youliang Wang ◽  
Raymond A. Poirier
Keyword(s):  
Activation Energy ◽  
Transition State ◽  
Ab Initio ◽  
Negative Charge ◽  
Enoic Acid ◽  
Electronic Charge ◽  
Theoretical Point ◽  
Cyclic Transition ◽  
Experimental Values ◽  
Thermal Decarboxylation

The mechanism for thermal decarboxylation of but-3-enoic acid and its derivatives HXC=CYCH2COOH (X, Y=H, F, CH3, C2H5, and Cl) leading to carbon dioxide and olefins has been studied from the theoretical point of view by ab initio MO calculations. The transition states obtained by our ab initio calculations are completely consistent with the experimental data, and support the "synchronous" mechanism for thermal decarboxylation of but-3-enoic acid and its derivatives via a "twisted chair" six-membered cyclic transition state. The effects of β- and γ-substituents on the activation energy (Ea) can be explained in terms of electronic charge distribution. β-Substitution decreases the activation energy, while γ-substitution increases it. Changes in the activation energy are related to changes in the charges at Cγ(C1) and Cβ(C2) as the substituents are varied. The activation energy decreases with an increase of negative charge at Cγ, while it increases with an increase of negative charge at Cβ. The best estimate of 156.8 kJ/mol for the activation energy with MP2/6-31G*//HF/3-21G(*) is in reasonable agreement with the available experimental values of 164 ± 7 kJ/mol and 160 kJ/mol for decarboxylation of but-3-enoic acid. The calculated primary kH/kD, 2.86, and [Formula: see text] 1.03, for the decarboxylation of but-3-enoic acid, are also in excellent agreement with the available experimental values of 2.7 and 1.035, respectively, supporting the transition state structure obtained.

A Versatile Software for Construction of the Master Sintering Curve

2018 ◽  
Vol 912 ◽  
pp. 240-244 ◽  
Author(s):  
Rafael Morgado Batista ◽  
J.F.R. Naranjo ◽  
Eliana Navarro Santos Muccillo
Keyword(s):  
Activation Energy ◽  
Kinetic Data ◽  
Data Evaluation ◽  
Doped Ceria ◽  
Microstructure Development ◽  
Metal Powders ◽  
Sintering Process

Several models have been developed over the last years to study the microstructure development of ceramic and metal powders during sintering. Among the most utilized methodology one may find the Arrhenius and the so-called Master Sintering Curve (MSC). Both models involve manipulation of a large number of data, and repetitive and time-consuming calculations. In this work, was developed a versatile and friendly-user software for a PC-type computer encompassing both methodologies. The software is flexible allowing for kinetic data evaluation such as the activation energy for sintering and sintering maps. Details of the software along with its application to investigate the sintering process of 10 mol% gadolinia-doped ceria are described.

A study of the mechanism of decay of alkyl macroradicals in isotactic polypropylene

1985 ◽  
Vol 50 (6) ◽  
pp. 1391-1401 ◽  
Author(s):  
Josef Bartoš ◽  
Jozef Tiňo
Keyword(s):  
Activation Energy ◽  
Isotactic Polypropylene ◽  
Kinetic Data ◽  
Molecular Mechanisms ◽  
Point Of View ◽  
Diffusion Limited ◽  
Region I ◽  
The Matrix ◽  
Region Ii ◽  
Two Temperature

The kinetic data of decay of alkyl macroradicals in two temperature regions in isotactic polypropylene exposed to gamma radiation at 77 K were interpreted in terms of the model of diffusion-limited reactions at the activation energy level. The potential molecular mechanisms of transfer of the radical centres were tested from the point of view of their physical and/or chemical migration. Two mechanisms are suggested for the mutual approach of the centres in macroradical decay regions I and II in the amorphous zones of the matrix. Both of them involve the contribution of segmental conformational motions, the mobility of the terminal segments being of importance in region I whereas in region II the mutual nearing of the reactants proceeds in a relay way via intermolecular H-abstraction in conjunction with crank and crankshaft motions of the end and inner segments of the chain.

Carbonyl Ylides and the Rearrangement of (+)-trans-2,3-Diisopropenyloxirane

1974 ◽  
Vol 52 (11) ◽  
pp. 2098-2101 ◽  
Author(s):  
Jean-Claude Paladini ◽  
R. J. Crawford
Keyword(s):  
Gas Phase ◽  
Kinetic Data ◽  
Ring Opening ◽  
Ring Closure ◽  
Carbonyl Ylide ◽  
Kinetics Of ◽  
Oxygen Bond

The kinetics of the gas phase racemization and rearrangement of 2,3-diisopropenyloxirane have been determined. Comparison with the kinetic data for 2,3-divinyloxirane allows us to exclude the mechanism for the formation of vinyldihydrofuran wherein an inward conrotatory ring opening comprises the first step. The mechanism proposed consists of an isomerization about the carbon–oxygen bond of the carbonyl ylide to form an isomeric intermediate which then undergoes a disrotatory five-centered ring closure to produce 2-isopropenyl-4-methyl-2,3-dihydrofuran.

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