THE REACTIVITY OF THE CYCLIC POLYENES TOWARDS FREE RADICALS: III. ADDITION OF THE ETHYL RADICAL

1965 ◽  
Vol 43 (5) ◽  
pp. 1110-1119 ◽  
Author(s):  
A. C. R. Brown ◽  
D. G. L. James
Keyword(s):  
Molecular Structure ◽  
Free Radicals ◽  
Gas Phase ◽  
Energy Of Activation ◽  
Kcal Mole ◽  
Arrhenius Parameters ◽  
Ethyl Radical ◽  
Cyclic Polyenes

Arrhenius parameters have been measured for the addition of the ethyl radical to cycloheptatriene-1,3,5 and to bicyclo[2.2.1]heptadiene-2,5 in the gas phase; the values for the energy of activation are distinct at 6.4 ± 0.2 and 7.0 ± 0.1 kcal/mole respectively. The addition of the ethyl radical to benzene, cyclohexadiene-1,4, and cyclooctadiene-1,5 proceeds too slowly to be detected. The significance of these results is considered in conjunction with those obtained previously for cyclohexadiene-1,3 and cyclooctatetraene, and the possibility of interpreting the reactivity of the cyclic polyenes in terms of molecular structure is discussed.

Reactions of the ethyl radical I. Metathesis with unsaturated hydrocarbons

1958 ◽  
Vol 244 (1238) ◽  
pp. 289-296 ◽  
Keyword(s):  
Molecular Structure ◽  
Experimental Error ◽  
Frequency Factor ◽  
Energy Of Activation ◽  
Kcal Mole ◽  
Hydrogen Atoms ◽  
Common Value ◽  
Ethyl Radical ◽  
Molecular Reactivity ◽  
Bond Multiplicity

The kinetic study of the abstraction of the hydrogen atom from selected hydrocarbons by the ethyl radical reveals a natural correspondence between molecular structure and molecular reactivity. Values of the energy of activation of the series n -heptane, 1-heptene and 1-heptyne are distinct at 10·6 ± 0·4, 8·3 ± 0·5 and 7·6 ± 0·2 kcal mole -1 , respectively, and illustrate the activating influence of bond multiplicity. The group of olefines: 1-heptene, 1-octene, cyclo hexene and trans -4-octene appear to share a common value of 8·3 kcal mole -1 for the energy of activation, within the limits of experimental error. Values of the frequency factor correspond closely to the numbers of equivalent hydrogen atoms in the molecule of the hydrocarbons.

REACTIONS OF THE ETHYL RADICAL: IV. ADDITION TO VINYL MONOMERS

1965 ◽  
Vol 43 (3) ◽  
pp. 633-639 ◽  
Author(s):  
D. G. L. James ◽  
Duncan MacCallum
Keyword(s):  
Gas Phase ◽  
Vinyl Monomers ◽  
Kcal Mole ◽  
Ethyl Radical ◽  
Wide Range ◽  
Exponential Factors ◽  
Representative Selection ◽  
Intrinsic Reactivity ◽  
Radical Attack ◽  
Selection Of

The Arrhenius parameters have been measured for the addition of the ethyl radical to a representative selection of vinyl monomers in the gas phase. The wide range of reactivity observed was almost entirely due to the variation of the energy of activation, from 3.4 ± 0.4 kcal/mole for acrylonitrile to 6.9 ± 0.5 kcal/mole for vinyl acetate. No significant variation was found among the values of the pre-exponential factors, indicating uniformity of steric conditions at the site of radical attack. The rate constant for the addition of the ethyl radical is considered as an alternative to the copolymerization parameter Q0 as an index of the intrinsic reactivity of a monomer at a given temperature.

REACTIONS OF THE ETHYL RADICAL: VI. ADDITION TO CONJUGATED DIENES

1965 ◽  
Vol 43 (5) ◽  
pp. 1102-1109 ◽  
Author(s):  
A. C. R. Brown ◽  
D. G. L. James
Keyword(s):  
Rate Constants ◽  
Chain Transfer ◽  
Conjugated Dienes ◽  
Energy Of Activation ◽  
Conjugated Diene ◽  
Kcal Mole ◽  
Hydrogen Atoms ◽  
Ethyl Radical ◽  
Diene System ◽  
Rate Constants For Addition

Arrhenius parameters have been measured for the addition of the ethyl radical to the conjugated diene system in three representative molecular environments. Significant differences are found among the values of the energy of activation for addition, which are: 4.5 ± 0.2 kcal/mole for 2,3-dimethylbutadiene-1,3, 5.2 ± 0.3 kcal/mole for cyclohexadiene-1,3, and 6.6 ± 0.3 kcal/mole for 2,5-dimethylhexadiene-2,4. The increase in the energy of activation in this series is paralleled by an increase in the degree of shielding of the terminal carbon atoms of the conjugated system by substituent groups. The energy of activation for metathesis is significantly lower for cyclohexadiene-1,3 (5.4 ± 0.5 kcal/mole) than for 2,5-dimethylhexadiene-2,4 (7.6 ± 0.4 kcal/mole); the activated hydrogen atoms of the former are all secondary, whereas those of the latter are all primary. The ratio of the rate constants for addition and metathesis at 60° indicate that the radical homopolymerization of cyclohexadiene-1,3 and 2,5-dimethylhexadiene-2,4 should be subject to extensive degradative chain transfer.

Catalysis by hydrogen halides in the gas phase. XVII. Isobutyric acid and hydrogen bromide

1968 ◽  
Vol 21 (3) ◽  
pp. 725 ◽  
Author(s):  
JTD Cross ◽  
VR Stimson
Keyword(s):  
Carbon Monoxide ◽  
Gas Phase ◽  
Rate Constants ◽  
Hydrogen Bromide ◽  
Isobutyric Acid ◽  
Kcal Mole ◽  
Hydrogen Halides ◽  
Arrhenius Parameters ◽  
First Order ◽  
Added Water

Hydrogen bromide catalyses the decomposition of isobutyric acid into propene, carbon monoxide, and water at 369-454�. Hydrogen bromide is not lost. Individual runs follow the first-order rate law, and the rate constants are proportional to the hydrogen bromide pressure. The Arrhenius parameters are: E = 33.17 kcal mole-1 and A = 1012.87 sec-1 ml mole-1, and the reaction is homogeneous and molecular. Added water or methanol retards the reaction.

Free-radical-catalyzed isomerization of isocyanides

1967 ◽  
Vol 45 (22) ◽  
pp. 2749-2754 ◽  
Author(s):  
D. H. Shaw ◽  
H. O. Pritchard
Keyword(s):  
Thermal Decomposition ◽  
Free Radical ◽  
Carbon Atom ◽  
Gas Phase ◽  
Methyl Radicals ◽  
Kcal Mole ◽  
Arrhenius Parameters ◽  
Reaction Proceeds ◽  
Methyl Isocyanide ◽  
Butyl Peroxide

The isomerization of methyl isocyanide and of ethyl isocyanide, catalyzed by methyl radicals produced in the thermal decomposition of di-tert-butyl peroxide, has been studied in the gas phase at temperatures near 100 °C. The Arrhenius parameters for the reaction CH3NC + CH3 → CH3 + CH3CN are E = 7.8 ± 0.3 kcal/mole and A = 1012.25 mole−1 cc s−1. It is proposed that the reaction proceeds by addition of the incoming radical to the divalent carbon atom of the isocyanide group, followed by expulsion of the radical originally attached to the N atom. The thermochemistry of addition to the divalent carbon atom is discussed in an Appendix.

DECOMPOSITION PRESSURES OF FERRIC SULPHATE AND ALUMINUM SULPHATE

1960 ◽  
Vol 38 (11) ◽  
pp. 2196-2202 ◽  
Author(s):  
N. A. Warner ◽  
T. R. Ingraham
Keyword(s):  
Gas Phase ◽  
Static System ◽  
Ferric Sulphate ◽  
Kcal Mole ◽  
Aluminum Sulphate ◽  
Temperature And Pressure ◽  
Pressure Changes ◽  
Mercury Manometer ◽  
Decomposition Pressure ◽  
Gas Pressures

The gas pressures over samples of anhydrous ferric sulphate and anhydrous aluminum sulphate have been measured in a static system, using a mercury manometer in which the exposed surface was covered with a flexible Pyrex bellows. The calculated ΔH for the decomposition of Fe2(SO4)3 was +135.4 kcal/mole. It was not possible to calculate the ΔH for the Al2(SO4)3 decomposition, because a discrete aluminum oxide with singular thermodynamic properties was not obtained.In the Fe2(SO4)3 system, the fraction of SO3 in the gas phase was found to be almost constant over the range of temperature and pressure changes used in the study.At any given temperature, the decomposition pressure over a ferric sulphate sample is greater than that over an aluminum sulphate sample, thus indicating that preferential decomposition of ferric sulphate should be thermodynamically feasible in mixtures of ferric sulphate and aluminum sulphate.

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