Photolyse du méthyl-2-butène-1, du méthyl-3-butène-1 et du cis-pentène-2 à 174, 163 et 147 nm

1979 ◽  
Vol 57 (8) ◽  
pp. 863-869 ◽  
Author(s):  
Guy J. Collin ◽  
Hélène Deslauriers ◽  
Sylvain Auclair
Keyword(s):  
Double Bond ◽  
Photon Energy ◽  
Rate Constant ◽  
Pressure Effect ◽  
Low Pressure ◽  
Decomposition Process ◽  
Fragmentation Process ◽  
Quantum Yields ◽  
Methyl Radicals ◽  
Hydrogen Atoms

Photolysis of 2-methyl-1-butene (M2B1), cis-2-pentene (CP2), and 3-methyl-1-butene (M3B1) has been systematically studied at 163 nm. Pressure effect has been measured at 147, 163, and 174 nm. The main fragmentation process of the photoexcited olefine is the C—C split of the bond located in position β relative to the double bond:[Formula: see text] α-Methallyl radicals obtained in the M3B1 and CP2 photolysis decompose partly at low pressure, giving rise to the formation of 1,3-butadiene and hydrogen atoms. β-Methallyl radicals decompose also at low pressure into allene and methyl radicals. Butadiene and allene quantum yields follow the Stern–Volmer law, and this allows us to determine the ratio of the rate constant of dissociation relative to the rate constant of stabilization, kd/ks, through collision of the α- and β-methallyl radicals. From these values, we conclude that the excess of photon energy is not statistically distributed into the fragments, and that the decomposition process follows one (or several) particular law(s).

Photolyse de pentène-1 dans l'ultraviolet à vide

1973 ◽  
Vol 51 (5) ◽  
pp. 724-731 ◽  
Author(s):  
Patrick M. Perrin ◽  
Guy J. Collin
Keyword(s):  
Double Bond ◽  
Low Pressure ◽  
Hydrogen Atoms ◽  
Ethyl Radical ◽  
Excited Molecules

Photolysis of 1-pentene molecules at 8.4 eV (xenon photolysis) and 10.0 eV (krypton photolysis) was studied. Excited molecules decompose to produce mainly ethylene, propadiene, 1,3-butadiene, acetylene, and other minor products. Hydrogen atoms add to the double bond of the monomer and the resulting excited pentyl radical decomposes at low pressure (P < 1 Torr) into propene and ethyl radical. Isomerization of excited 1-pentene molecules is unimportant at these energies.

The reaction of hydrogen atoms with ethylene

1970 ◽  
Vol 316 (1527) ◽  
pp. 575-591 ◽  
Keyword(s):  
Hydrogen Atom ◽  
Rate Constant ◽  
Recombination Reaction ◽  
Methyl Radicals ◽  
Methyl Radical ◽  
Hydrogen Atoms ◽  
Ethyl Radical ◽  
Cracking Reaction ◽  
Computer Calculations ◽  
First Time

A detailed study has been made of the products from the reaction between hydrogen atoms and ethylene in a discharge-flow system at 290 ± 3 K. Total pressures in the range 8 to 16 Torr (1100 to 2200 Nm -2 ) of argon were used and the hydrogen atom and ethylene flow rates were in the ranges 5 to 10 and 0 to 20 μ mol s -1 , respectively. In agreement with previous work, the main products are methane and ethane ( ~ 95%) together with small amounts of propane and n -butane, measurements of which are reported for the first time. A detailed mechanism leading to formation of all the products is proposed. It is shown that the predominant source of ethane is the recombination of two methyl radicals, the rate of recombination of a hydrogen atom with an ethyl radical being negligible in comparison with the alternative, cracking reaction which produces two methyl radicals. A set of rate constants for the elementary steps in this mechanism has been derived with the aid of computer calculations, which gives an excellent fit with the experimental results. In this set, the values of the rate constant for the addition of a hydrogen atom to ethylene are at the low end of the range of previously measured values but are shown to lead to a more reasonable value for the rate constant of the cracking reaction of a hydrogen atom with an ethyl radical. It is shown that the recombination reaction of a hydrogen atom with a methyl radical, the source of methane, is close to its third-order region.

The photolysis of 2,3- and 3,3-dimethyl-1-butene at 147.0 and 184.9 nm

1985 ◽  
Vol 63 (1) ◽  
pp. 62-67 ◽  
Author(s):  
Hélène Deslauriers ◽  
Guy J. Collin
Keyword(s):  
Quantum Yield ◽  
Gas Phase ◽  
Electronic State ◽  
Photon Energy ◽  
Low Pressure ◽  
Decomposition Process ◽  
Primary Decomposition ◽  
Primary Process ◽  
The One

The photofragmentation of 2,3-dimethylbutene and 3,3-dimethylbutene has been studied at 147 and 184.9 nm in the gas phase. The main primary decomposition process at both wavelengths involves the rupture of a β(C—C) bond. The quantum yield for this process is higher than 0.7 at 147 nm and is probably even higher at 184.9 nm. All dimethallyl radicals formed at 147 nm in this process decompose at low pressure, but some of them isomerize from the α,β- to the α,α- structure (and vice versa) — via a 1,4-H transfer — before decomposition. At 184.9 nm, the same primary process is used to get a rough value for the lifetime of the photoexcited molecule, compared with the one made with RRKM calculations by assuming that all the photon energy resides in the vibrational framework of the fundamental electronic state. These lifetimes are about one nanosecond or less.

The kinetics of the interaction of atomic hydrogen with olefines. V. Results obtained for a further series of compounds

1950 ◽  
Vol 202 (1069) ◽  
pp. 181-202 ◽  
Keyword(s):  
Double Bond ◽  
Hydrogen Atom ◽  
Atomic Hydrogen ◽  
Methyl Radicals ◽  
Hydrogen Atoms ◽  
Alkyl Radicals ◽  
Kinetics Of ◽  
Interesting Generalization

In this paper the efficiency of interaction of a hydrogen atom with a series of olefines has been determined, the olefines being members of the series obtained by progressively replacing the hydrogen atoms of ethylene by methyl radicals. The interesting generalization which emerges from this is that the efficiency of interaction does not vary very much with the nature of the alkyl substituents in the molecule, and calculations involving the heats of addition of a hydrogen atom to a double bond confirm this generalization. The data presented here are discussed critically in relation to information available on the reaction of CCl 3 radicals with olefines and of alkyl radicals with olefines, complete general agreement being demonstrated.

The reaction of free radicals with trichlorosilane

1967 ◽  
Vol 20 (8) ◽  
pp. 1545 ◽  
Author(s):  
TN Bell ◽  
BB Johnson
Keyword(s):  
Free Radicals ◽  
Quantitative Study ◽  
Rate Constant ◽  
Methyl Radicals ◽  
Hydrogen Atoms ◽  
Experimental Conditions ◽  
Chlorine Atoms

Trifluoromethyl radicals generated from the photolysis of hexafluoroacetone abstract hydrogen atoms from trichlorosilane; the competitive abstraction of chlorine atoms does not occur under the experimental conditions. The rate of the abstraction ������� �����������������CF3 + SiHCl3 → CF3N + SiCl3 has been measured in comparison with the known rate for the recombination of trifluoromethyl radicals, to yield a rate constant, ������������������ k = 1012.13exp(-6850/RT) ml mole-1 sec-1 Methyl radicals similarly abstract hydrogen to yield methane. A quantitative study of this reaction proved impractical, due to complications using acetone as a radical source.

Ion–molecule reactions in dimethylsulfoxide by high pressure photoionization mass spectrometry

1980 ◽  
Vol 58 (4) ◽  
pp. 376-380 ◽  
Author(s):  
John A. Stone ◽  
Margaret S. Lin
Keyword(s):  
Mass Spectrometry ◽  
High Pressure ◽  
Photon Energy ◽  
Rate Constant ◽  
Pressure Range ◽  
Low Pressure ◽  
Photoionization Mass Spectrometry ◽  
Ion Molecule Reactions

Dimethylsulfoxide (DMSO) has been photoionized at 10.0 and 11.7 eV over the pressure range 0.3–210 mTorr. The rate constant for the disappearance of DMSO+ is 1.0 × 10−9 cm3 molecule−1 s−1, independent of photon energy. The major products at low pressure are CH3SO(CH3SO)CH3+ and CH3SOHCH3+ while at high pressure the ion series (DMSO)nH+ predominates with n ≤ 5. In experiments with mixtures of DMSO and water or methanol very little mixed solvation of the proton was observed although isotopic D/H exchange between D2O and (DMSO)2H+ is facile.

The addition of methyl radicals to ethylene, propylene, the butenes and higher 1-olefines

1957 ◽  
Vol 240 (1222) ◽  
pp. 396-407 ◽  
Keyword(s):  
Double Bond ◽  
Carbon Atom ◽  
Rate Constants ◽  
Relative Rate ◽  
Methyl Radicals ◽  
Active Hydrogen ◽  
Hydrogen Atoms ◽  
Methyl Group ◽  
Ethylene Propylene ◽  
Relative Rate Constants

The addition of methyl radicals to ethylene and its homologues in iso -octane solution was studied over the temperature range 55 to 85°C. The relative rate constants of addition to ethylene, propylene and iso -butene determined at 65°C are 34, 22 and 36 respectively. Taking into account the statistical factor of 2 for ethylene, we conclude that the increasing ease of addition for this series of olefines reflects the increasing stability of the produced radicals. The rates of addition to trans - and cis -butene-2 are significantly lower (6.9 and 3.4 respectively), indicating a steric hindrance resulting from the presence of a methyl group on the carbon atom on which the reaction takes place. Identical rates of addition were found for propylene, butene-1,pentene-1, 3 methyl butene-1, heptene-1, decene-1 and hexadecene-1, indicating that the rates of addition are not affected by the length and the shape of the hydro­carbon ‘tail’. The rates of abstraction of hydrogen atoms by methyl radicals were determined. It was found that the rate constants for active hydrogen ( α to C=C double bond) fall into three distinctive classes characterizing the primary, the secondary, and the tertiary hydrogen atoms.

Decomposition Process of Benzene in a Low Pressure DC Glow Discharge

2010 ◽  
Vol 130 (11) ◽  
pp. 1004-1008
Author(s):  
Shinobu Hayashi ◽  
Kohki Satoh ◽  
Hidenori Itoh
Keyword(s):  
Glow Discharge ◽  
Low Pressure ◽  
Decomposition Process ◽  
Dc Glow Discharge

Mechanistic studies of aromatic ketone-sensitized photoreduction of bis(acetylacetonato)copper(II)

1983 ◽  
Vol 61 (5) ◽  
pp. 801-808 ◽  
Author(s):  
Yuan L. Chow ◽  
Gonzalo E. Buono-Core ◽  
Bronislaw Marciniak ◽  
Carol Beddard
Keyword(s):  
Rate Constant ◽  
Rate Constants ◽  
Flash Photolysis ◽  
Decay Rates ◽  
Polynuclear Aromatic Hydrocarbons ◽  
Aromatic Ketone ◽  
Quantum Yields ◽  
Triplet States ◽  
Quenching Rate ◽  
Triplet Energy

Bis(acetylacetonato)copper(II), Cu(acac)2, quenches triplet excited states of ketones and polynuclear aromatic hydrocarbons efficiently, but only aromatic ketones with high triplet energy successfully sensitize photoreduction of Cu(acac)2 in alcohols under nitrogen to give derivatives of aeetylacetonatocopper(I), Cu(acac). For the triplet state benzophenone-sensitized photoreduction of Cu(acac)2, the quantum yields of photoreduction (ΦC) and those of benzophenone disappearance (ΦB) were determined in methanol with various concentrations of Cu(acac)2. The values of the quenching rate constant, kq, determined from these two types of monitors on the basis of the proposed mechanism were in good agreement (6.89 ~ 7.35 × 109 M−1 s−1). This value was higher, by a factor of about two, than that obtained from the monitor of the benzophenone triplet decay rates generated by flash photolysis in the presence of Cu(acac)2. The quenching rate constants of various aromatic ketone and hydrocarbon triplet states by Cu(acac)2 were determined by flash photolysis to be in the order of the diffusion rate constant and the quantum yields of these photoreductions were found to be far from unity. Paramagnetic quenching, with contributions of electron exchange and charge transfer, was proposed as a possible quenching mechanism. For a series of aromatic ketone sensitizers with higher triplet energy, this mechanism was used to rationalize the observed high quenching rate constants in contrast to the low quantum yields of photoreduction.

Sign in / Sign up

Export Citation Format

Share Document