Gas‐phase reactions of Cl atoms with propane,n‐butane,and isobutane

Using the relative kinetic method, rate coefficients have been determined for the gas‐phase reactions of chlorine atoms with propane, n‐butane, and isobutane at total pressure of 100 Torr and the temperature range of 295–469 K. The Cl₂ photolysis (λ = 420 nm) was used to generate Cl atoms in the presence of ethane as the reference compound. The experiments have been carried out using GC product analysis and the following rate constant expressions (in cm³ molecule^?1 s^?1) have been derived: (7.4 ± 0.2) × 10^?11 exp [‐(70 ± 11)/ T], Cl + C₃H₈ → HCl + CH₃CH₂CH₂; (5.1 ± 0.5) × 10^?11 exp [(104 ± 32)/ T], Cl + C₃H₈ → HCl + CH₃CHCH₃; (7.3 ± 0.2) × 10^?11 exp[?(68 ± 10)/ T], Cl + n‐C₄H₁₀ → HCl + CH₃ CH₂CH₂CH₂; (9.9 ± 2.2) × 10^?11 exp[(106 ± 75)/ T], Cl + n‐C₄H₁₀ → HCl + CH₃CH₂CHCH₃; (13.0 ± 1.8) × 10^?11 exp[?(104 ± 50)/ T], Cl + i‐C₄H₁₀ → HCl + CH₃CHCH₃CH₂; (2.9 ± 0.5) × 10^?11 exp[(155 ± 58)/ T], Cl + i‐C₄H₁₀ → HCl + CH₃CCH₃CH₃ (all error bars are ± 2σ precision). These studies provide a set of reaction rate constants allowing to determine the contribution of competing hydrogen abstractions from primary, secondary, or tertiary carbon atom in alkane molecule. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 651–658, 2002     

Rate constant and products for the reaction of Cl atom with n‐butyraldehyde

The photooxidations of n‐butyraldehyde initiated by Cl atom were carried out at room temperature (298 ± 2K) and 1 atm pressure. The rate coefficient for the reactions of Cl atom with n‐butyraldehyde was determined as k = (2.04 ± 0.36) × 10^?10 cm³ molecule^?1 s^?1 by using relative rate techniques. The photooxidation products of n‐butyraldehyde reaction with Cl atom were also studied by using both gas chromatography‐mass spectrometry (GC‐MS) and gas chromatography techniques. C₂H₅CHO, CH₃CHO, CO and CO₂ were the major products observed. In the absence of NO, the observed yields of C₂H₅CHO, CH₃CHO, and CO were 60%, 3%, and 9%, respectively. However, when NO was introduced into the reaction chamber and the initial ratios of [NO]₀/[n‐butyraldehyde]₀ were between 1 and 8, the yield of C₂H₅CHO decreased to 33%, whereas that of CH₃CHO and CO rose up to 21% and 25%, respectively. On the basis of mechanism data deduced in this study and the fraction molar yields, the approximate branching ratios for Cl atom attack at ? C(O)H, α‐, β‐, and γ‐positions in n‐butyraldehyde could be derived as ?42%, <25%, 21%, and ?12%, respectively. © 2007 Wiley Periodicals, Inc. 39: 168–174, 2007     

Photochemistry of methyl- and n1-benzyl-n5-cyclopentadienyltricarbonyltungstein(II)

Irradiation of solutions of n⁵-C₅H₅W(CO)₃R (R  CH₃n1-CH₂C₆H₅) in cyclohexane at ca. 310490 nm leads to the formation of [n⁵-C₅H₅W(CO)₃]₂ and methane and of n⁵-C₅H₅W₅(CO)₂(n³-CH₂C₆H₅) and some [n⁵-C₅H₅W(CO)₃]₂, respectively. When the irradiation is carried out in the presence of excess P(C₆H₅)₃, the photoproducts are n⁵-C₅H₅W(CO)₂[P(C₆H₅)₃]CH₃ (R  CH₃) and n⁵-C₅H₅W(CO)₂(n₃-CH₂C₆H₅) and trace [n⁵-C₅H₅W(CO)₃]₂ (R  n¹-CH₂C₆H₅). Photolysis of the n⁵-C₅H₅W(CO)₃R in the presence of benzyl chloride affords n⁵-C₅H₅W(CO)₃Cl (R  CH₃) and both n⁵-C₅H₅W(CO)₂(n³-CH₂C₂H₅) and n⁵-C₅H₅W(CO)₃Cl (R  n¹-CH₂C₆H₅), the relative amounts of the latter products depending on the quantity of added C₆H₅CH₂Cl. Irradiation of n⁵-C₅H₅W(CO)₃-CH₃ in the presence of both P(C₆h₅)₃ and C₆H₅CH₂Cl affords n⁵-C₅H₅W(CO)₂-[P(C₆H₅)₃]CH₃, but no n⁵-C₅H₅W(CO)₃Cl. It is proposed that the primary photo-reaction in these transformations is dissociation of a CO group from n⁵-C₅H₅W-(CO)₃R to generate n⁵-C₅H₅W(CO)₂R, which can either combine with L to form a stable 18 electron complex, n⁵-C₅H₅W(CO)₂(L)R (L  CO, P(C₅H₅)₃; LR  n³-CH₂C₆H₅), or lose the group R in a competing, apparently slower step. This proposal receives support from the observation that, light intensifies being equal, n⁵-C₅H₅W(CO)₃CH₃ undergoes a considerably faster photoconversion to [n⁵-C₅H₅W(CO)₃]₂ under argon than under carbon monoxide.     

N,N′-methylenedipyridinium Pt(II) and Pt(IV) hybrid salts: synthesis, crystal and molecular structures of [(C5H5N)2CH2] · [PtCl4] and [(C5H5N)2CH2] · [PtCl6]

The highly insoluble organic-inorganic hybrid ionic compounds N,N??-methylenedipyridinium tetrachloroplatinate(II) [(C₅H₅N)₂CH₂] · [PtCl₄] and N,N??-methylenedipyridinium hexachloroplatinate(IV) [(C₅H₅N)₂CH₂] · [PtCl₆] were obtained by the treatment of N,N??-methylenedipyridinium dichloride monohydrate [(C₅H₅N)₂CH₂]Cl₂ · H₂O with K₂[PtCl₄] or (NH₄)₂[PtCl₆], respectively, in an aqueous solution. Both complexes were isolated, purified, characterised by elemental analysis, and their molecular structures were confirmed by powder X-ray diffraction. The crystal structure of both compounds consists of separated discrete dications [(C₅H₅N)₂CH₂]²⁺ and anions [PtCl _n ]^2? (n = 4 or 6). As anticipated, the dications formed a butterfly shape consisting of two pyridine rings bound to the methylene group via their N atoms, while the Pt centre had a square planar geometry in [(C₅H₅N)₂CH₂] · [PtCl₄] and an octahedral coordination in [(C₅H₅N)₂CH₂] · [PtCl₆]. Interestingly, both crystal structures are stabilised by intermolecular C-H??Cl non-standard hydrogen bonds, ??-?? ring interactions between two pyridine rings of adjacent dications, and also by Cl-?? interactions.     

Komplexbildung des tert-Butyliminovanadium(V)-trichlorids mit O-Donor-Liganden

Coordination Compounds of tert-Butyliminovanadium(V) Trichloride with O-Donor-Ligands The reaction of tert-butyliminovanadium(V)trichloride ( 1 ) with cyclic and acyclic ethers, ethylene carbonate and thietane has been studied. The 1:1-complexes have a different stability; reversible and irreversible cleavage of ether in the coordination sphere of the vanadium atom rearranging in ω-chloroalkanolato ligands are observed. The reaction of 1 with 2-chloroethanol, 3-chloropropanol and 5-chloropentanol yields the complexes ^tC₄H₉N = V(OR)Cl₂ (R = CH₂CH₂CH₂CH₂CH₂Cl) and [^tC₄H₉N = V(OR)Cl₂ · ROH]; in the presence of triethylamine the disubstituted compounds ^tC₄H₉N = V(OR)₂Cl are formed. The ⁵¹V NMR spectra are discussed. The crystal structure of [^tC₄H₉N = VCl₃ · DME] ( 12 ) and [^tC₄H₉N = V(OCH₂CH₂Cl)Cl₂ · HOCH₂CH₂Cl] ( 13 ) has been determined. The vanadium atoms in 13 have a distorted octahedral coordination and are linked by the oxygen atoms of the 2-chloroethanolato ligands forming a binuclear complex. In solution molecular weight measurement and ⁵¹V NMR data indicate the equilibrium between a mononuclear complex 13 and its isomer [^tC₄H₉N = V(OCH₂CH₂Cl)₂Cl · HCl].     

Säureinduzierte carbin-acylumwandlung

The reaction of dicarbonyl- and carbonyl(trimethylphosphine)(cyclopentadienyl)-carbyne complexes of molybdenum and tungsten η⁵-C₅H₅(CO)_2−n(PMe₃)_nMCR (n = 0, 1; M = Mo, W; R = CH₃, C₆H₅, C₆H₄CH₃, C₃H₅) with protic nucleophiles HX (X = Cl, CF₃COO, CCl₃COO) leads, through a combined protonation/carbon-carbon coupling reaction, to η²-acyl complexes η⁵-C₅H₅(CO)_1−nX₂(PMe₃)_n-M(η²-COCH₂R). The reaction conditions, the results of the spectroscopic measurements and the X-ray structure of η⁵-C₅H₅(CO)(Cl₂)W(η²-COCH₂CH₃) are reported.     

Coordination compounds of cobalt, nickel, copper and zinc with thiosemicarbazone and 3-phenylpropenal semicarbazone

Hydrates of 3-phenylpropenal thiosemicarbazone (HL·H₂O) and semicarbazone (HL′·H₂O) react in methanol with cobalt, nickel, copper, and zinc chlorides, nitrates, and acetates to form coordination compounds MX₂·2HL·nSolv [M = Co, Ni, Cu, Zn; X = Cl, NO₃; HL = C₆H₅CH=CH-CH=N-NHC(O)NH₂; n = 0–3; Solv = H₂O, CH₃OH], CuX₂·HL·nH₂O [M = Ni, Cu; n = 0, 1], ML₂·nH₂O and ML′·nH₂O [M = Co, Ni, Zn; HL′ = C₆H₅CH=CH-CH=N-NHC(O)NH₂; n = 0–3]. In the presence of amines (A = C₅H₅N, 2-CH₃C₅H₄N, 3-CH₃C₅H₄N, and 4-CH₃C₅H₄N) these reactions yield the complexes Cu(A)LCl·CH₃OH and M(A)LX·nH₂O [M = Cu, Ni; X = Cl, NO₃; n = 0–2]. The copper complexes with the amine ligands are of polynuclear structure, and other complexes are monomeric. Carbazones (HL and HL′) are included in the complexes as bidentate N,S-and N,O-ligands. The thermolysis of the complexes involves the stages of removing solvent crystallization molecules (70–90°C), deaquation (150–170°C), and full thermal decomposition (500–580°C).     

The inductive effect of a radical center and transferability of the properties of functional groups in <Emphasis Type="Italic">n</Emphasis>-alkyl radicals

Electron density distribution in n-alkyl radicals (from ethyl to n-octyl) was studied by the B3LYP/6-311++G(3df,3pd) DFT method. The theory of atoms in molecules was used to show that the inductive effect of a free valence extends to two neighboring CH₂ groups. The electronegativities χ(C^?H₂) > χ(CH₃) > χ(CH₂) of groups and χ(C^?) > χ(H) > χ(C) atoms were qualitatively determined. The group method for calculating the enthalpies of formation of n-alkyl radicals Δ_f H°(n-C _n H_{2n+ 1}, n > 5) was substantiated.     

(Liquid + liquid) equilibrium in binary systems of isomeric C8 aliphatic monoethers with acetonitrile and its interpretation by the COSMO-SAC model

The (liquid + liquid) solubility curves have been determined by a synthetic method for six binary mixtures of [acetonitrile + {heptyl methyl ether CH₃OⁿC₇H₁₅, or ethyl hexyl ether C₂H₅OⁿC₆H₁₃, or pentyl propyl ether ⁿC₃H₇OⁿC₅H₁₁, or isopentyl propyl ether ⁿC₃H₇Oⁱ C₅H₁₁, or dibutyl ether ⁿC₄H₉OⁿC₄H₉, or butyl isobutyl ether ⁿC₄H₉OⁱC₄H₉}]. The possibility of the COSMO-SAC model to account for the thermodynamic differences between these systems has been tested and the discussion on the influence of screening charge of ethers on the system properties was undertaken.     

Differential thermal analysis of n-long chain alcohols and corresponding alkoxy ethanols

The differential thermal analyses of n-long chain alcohols CH₃(CH₃)_n-1-OH, designated as C_n-OH (n = 16, 18, 20 and 22), and corresponding alkoxy ethanols CH₃(CH₂)_n-1-OCH₂CH₂OH, designated as C_n-OC₂H₄OH, have been carried out at a heating rate of 1°C min^?1. The differential e.m.f (ΔV) has been plotted against the temperature of the reference material (°C) and the onset of the peak has been taken as the appearance of the polymorphic phase transition or melting of the compound. Heats of transition (ΔH₁) and melting or fusion (ΔH_f) were computed from the areas under the respective peaks.     

Cyclisierung neuer Trimethylsilylalkylaminohalogensilane

Cyclisation of New Trimethylsilylalkylaminohalosilanes Compounds of the composition RSiCl₂NR′SiMe₃ (R = Cl, CH₃, C₂H₅, C₆H₅; R′ = CH₃, C₂H₅, C(CH₃)₃) are obtained by the reaction of silicon halides with the lithium salts of silylamines. Under suitable experimental conditions the reaction leads to the formation of the corresponding Si? N four- and six-membered ring systems (RSiHalNR′)_n (Hal = F, Cl; n = 2 or 3) under elimination of trimethylhalosilane. The i.r., mass, ³⁵Cl-n.q.r., ¹H and ¹⁹F-n.m.r. spectra of these compounds are reported.     

Radiation effects of paraffins as polymer model compounds—I. Evolved gas analysis

Radiation yields of gases from n-paraffins of n-C₂₀H₄₂ to n-C₂₄H₅₀ and squalane (C₃₀H₆₂), as polymer model compounds, in the liquid and solid phases were analyzed by gas chromatography. G(H₂) in the liquid phase was 3.2–3.3 for all samples and found to be almost independent of the chemical structure and molecular weight; G(H₂) in the crystalline state of n-paraffins was 2.2–2.5 at -77 to 25°C. G(CH₄) was about 1% of G(H₂) for n-paraffins and increased with the methyl content of the branched chain for squalane. G(C₂H₆) in the liquid phase was about 0.05 for n-paraffins, but G(C₂H₆) in the crystalline state was found to depend on the crystal structure; that is, nearly zero for triclinic of an even number of carbons and about 0.02 for orthorhombic of an odd number. C₃H₈ and C₂H₄(C₃H₆ in squalane) were observed only in the liquid phase of n-paraffins and in glass and the liquid phase of squalane; G(C₃H₈) = 0.03–0.05 and G(C₂H₄ or C₃H₆) = 0.01–0.03. But the C₄-compounds were not detected in any phase of any of the samples.Chain scission by radiation is supposed to proceed mainly at chain end carbons until the third carbon in the liquid phase of n-paraffins, only at the chain end carbon of the crystalline surface in triclinic crystals and at chain end carbons until the second carbon in orthorhombic crystals. These chain scission phenomena in the liquid phase and crystalline state of n-paraffins and in the liquid phase of squalane would be analogous to those in the amorphous and crystalline states of polyethylene, and in amorphous ethylene-propylene copolymer, respectively.     

Selected rate constants for H,O, N,and Cl atoms with substrates at room temperatures

Rate constants for H + Cl₂, H + CH₃CHO, H + C₃H₄, O + C₃H₆, O + CH₃CHO, and Cl + CH₄ have been measured at room temperature by the discharge flow—resonance fluorescence technique. The results are (1.6 ± 0.1) × 10^?11, (9.8 ± 0.8) × 10 ^?14, (6.3 ± 0.4) × 10^{?13) (2.00 torr He), (3.95 ± 0.41) × 10?12, (4.9 ± 0.5) × 10|su?13} and (1.08 ± 0.07) × 10^?13, respectively, all in units of cm³ molecule^?1 s^?1. Also N atom reactions with C₂H₂, C₂H₄, C₃H₄, and C₃H₆ were studied but in no case was there an appreciable rate constant. These results are compared to previous studies.     

Study of the electric dipole moments of the (C2H5)n PX3−n and P{EIVB (CH3)3}3 compounds (X = Cl,Br, I; EIVB = C,Si, Sn; n = 0, 1, 2, 3)

The dipole moments of the (C₂H₅)_nPX_3?n (X = Cl, Br, I; n = 0, 1, 2, 3) and P{E^IVB(CH₃)₃}₃ compounds (E^IVB = C, Si, Sn) have been determined by dielectric measurements in benzene at 25°C by Higasi's method. The results are interpreted in terms of an additive vector model from bond moment calculations and a maximum phosphorus lone pair contribution of 1.75 D as calculated for P(C₂H₅)₃. The high dipole moment of the mixed PA₂B-type compounds in comparison with PA₃ moments is mainly ascribed to a loss of C_3v symmetry, characterized by a quite asymmetric orientation of the phosphorus lone pair with respect to the phosphorus bonding orbitals.     

Reactions of sodium tetrahydroborate with alkyl and aryl halides: A new approach to the synthesis of B3H 8 − and B12H 12 2− anions

A new method for the synthesis of the B₃H ₈ ^? anion based on the reactions of alkyl and aryl halides (C₂H₄Cl₂, C₆H₅CH₂Cl, C₄H₉Br, (C₆H₅)₃CCl, C₁₀H₇CH₂Cl, CH₂I₂, C₂HCl₃) with sodium tetrahydroborate in diglyme was proposed. The method is characterized by high (up to quantitative) yields and easy isolation of the target products, (n-C₄H₉)₄N)[B₃H₈] and Cs[B₃H₈], and also easy preparation of a salt of higher hydroborate anion, B₁₂H ₁₂ ^2? , without multistage purification from impurities of other anions of this series.     

Stibinidenkomplexe: Verbindungen mit trigonal planar koordiniertem antimon

Intensively coloured stibinidene complexes (L_nM)₂SbR (L_nM = (CO)₅Cr; R = ^tBu, Cl, I, EtS. L_nM = C₅H₅(CO)₂Mn; R = Cl. L_nM = CH₃C₅H₄(CO)₂Mn; R = Br) which contain trigonally planar coordinated Sb(+1) with the stibanediyl ligand stabilized by M $\text{?}$ Sb(R) $\text{?}$ M-π-bonding have been obtained. Their synthesis and properties as well as an X-ray structure determination of [CH₃C₅H₄(CO)₂Mn]₂SbBr are described.     

Synthesis of hetero-binuclear derivatives of the tetrathiolato complexes [Mo(η-C5H5CH2SR)2)], R = Prn and Ph,with platinum,palladium, and rhodium

The compound Mo(η-C₅H₄(CH₂)₂SPrⁿ)₂(SPrⁿ)₂ acts as a bidentate ligand giving the heteronuclear bi-metallic compounds [Mo(η-C₅H₄CH₂CH₂SPrⁿ)₂-(SPrⁿ)₂(PtCl₂)],[Mo(η-C₅H₄CH₂CH₂SPrⁿ)₂(SPrⁿ)₂(PdCl₂)₂], [Mo(η-C₅C₄CH₂CH₂SPrⁿ)₂(SPrⁿ)₂(RhCl₃)₂], [Mo(η-C₅H₄CH₂CH2SPrⁿ)₂(μ-SPrⁿ)₂Rh(dppe)]BF₄, [Mo(η-C₅H₄CH₂CH₂SPrⁿ)₂(μ-SPrⁿ)₂(COD)Rh]Cl, [Mo(η-C₅H₄CH₂CH₂SPrⁿ)₂-(μ-SPrⁿ)₂Pt(PPh₃)₂](PF₆)₂, and the compound [Mo(η-C₅H₄(CH₂)₂-μ-SPh)₂Cl₂Rh(COD)]Cl bonds via the ring-sulphur substituents giving [Mo(η-C₅H₄(CH₂)₂-μ-SPh)₂-Cl₂Rh(COD)]Cl.     

Synthesis,Structure, and Fluxionality of Strained Hypercoordinate Silicon‐Bridged [1]Ferrocenophanes

The first hypercoordinate sila[1]ferrocenophanes [fcSiMe(2‐C₆H₄CH₂NMe₂)] ( 5 a ) and [fcSi(CH₂Cl)(2‐C₆H₄CH₂NMe₂)] ( 5 b ) (fc=(η⁵‐C₅H₄)Fe(η⁵‐C₅H₄)) were synthesized by low‐temperature (?78 °C) reactions of Li[2‐C₆H₄CH₂NMe₂] with the appropriate chlorinated sila[1]ferrocenophanes ([fcSiMeCl] ( 1 a ) and [fcSi(CH₂Cl)Cl] ( 1 d ), respectively). Single‐crystal Xray diffraction studies revealed pseudo‐trigonal bipyramidal structures for both 5 a and 5 b , with one of the shortest reported Si???N distances for an sp³‐hybridized nitrogen atom interacting with a tetraorganosilane detected for 5 a (2.776(2) Å). Elongated Si? C_ipso bonds trans to the donating NMe₂ arms (1.919(2) and 1.909(2) Å for 5 a and 5 b , respectively) were observed relative to both the non‐trans bonds ( 5 a : 1.891(2); 5 b : 1.879(2) Å) and the Si? C_ipso bonds of the non‐hypercoordinate analogues ([fcSiMePh] ( 1 b ): 1.879(4), 1.880(4) Å; [fcSi(CH₂Cl)Ph] ( 1 e ): 1.881(2), 1.884(2)). Solution‐state fluxionality of 5 a and 5 b , suggestive of reversible coordination of the NMe₂ group to silicon, was demonstrated by means of variable‐temperature NMR studies. The ΔG^≠ of the fluxional processes for 5 a and 5 b in CD₂Cl₂ were estimated to be 35.0 and 37.6 kJ mol^?1, respectively (35.8 and 38.3 kJ mol^?1 in [D₈]toluene). The quaternization of 5 a and 5 b by MeOTf, to give [fcSiMe(2‐C₆H₄CH₂NMe₃)][OTf] ( 7 a‐ OTf) and [fcSi(CH₂Cl)(2‐C₆H₄CH₂NMe₃)][OTf] ( 7 b‐ OTf), respectively, supported the reversibility of NMe₂ coordination at the silicon center as the source of fluxionality for 5 a and 5 b . Surprisingly, low room‐temperature stability was detected for 5 b due to its tendency to intramolecularly cyclize and form the spirocyclic [fcSi(cyclo‐CH₂NMe₂CH₂C₆H₄)]Cl ( 9 ‐Cl). This process was observed in both solution and the solid state, and isolation and Xray characterization of 9 ‐Cl was achieved. The model compound, [Fc₂Si(2‐C₆H₄CH₂NMe₂)₂] ( 8 ), synthesized through reaction of [Fc₂SiCl₂] with two equivalents of Li[2‐C₆H₄CH₂NMe₂] at ?78 °C, showed a lack of hypercoordination in both the solid state and in solution (down to ?80 °C). This suggests that either the reduced steric hindrance around Si or the unique electronics of the strained sila[1]ferrocenophanes is necessary for hypercoordination to occur.     

Phase equilibria in the water-alkali metal or ammonium sulfate-synthanol systems

Solubility was studied for the first time in ternary aqueous phase-separating systems containing synthanol DS-10 or ALM-10 (polyethylene glycol monoalkyl ethers based on primary fatty alcohols, C _n H_{2n ? 1}O(C₂H₄O) _m H, where m = 8–10 and n = 10–18 (synthanol DS-10) or 12–14 (synthanol ALM-10)) and inorganic salt (NH₄)₂SO₄, Na₂SO₄, or Li₂SO₄ at 25°C. The boundaries of two-phase liquid equilibrium regions were determined. It was proposed to use the studied phase-separating systems for liquid extraction of metal ions.     

Minor processes in the photolysis of azomethane at low pressure: An upper limit for the rate of the unimolecular elimination of H2 from vibrationally excited ethane

The photolysis of azomethane in the near UV has been studied at room temperature and pressures from 10 mtorr to 10 torr. The main products, C₂H₆ and N₂, accounted for more than 99% of the reaction. Minor hydrocarbon products observed were (with quantum yields) C₃H₈ (3.5 × 10^?3), C₂H₄ (3.2 × 10^?4), CH₄ (3 × 10^?3), and n-C₄H₁₀ (trace). Quantum yields of H₂ of 4 × 10^?5 and 2 × 10^?5 were measured at azomethane pressures of 0.1 and 1.0 torr, respectively. The minor hydrocarbon products can be accounted for by reactions of CH₃ and C₂H₅ radicals following hydrogen abstraction from azomethane by CH₃. The H₂ product observed represents an upper limit for the H₂ elimination from vibrationally excited C₂H₆ formed by CH₃ combination in the system, corresponding to a rate of elimination ca. 5 × 10^?5 times the competing rate of dissociation to 2CH₃. Assuming a frequency factor of 10¹³ s^?1 for the H₂ elimination, a lower limit of about 90 kcal mol^?1 was estimated for the energy barrier.