Methane isotopically labelled

Methylzinc hydride was formed by the insertion of excited zinc atoms, in their 3Pi state, into the C-H bond of methane in an argon matrix.229 The MeZnH product was characterized on the basis of its infrared spectrum and determined to be a linear molecule with C v symmetry. The band at 1866.1 cm-1 is due the Zn-H stretch, while the band at 565.5 cm-1 was assigned to the Zn-C stretching vibration. Additional bands for isotopically labeled species were also reported. 

Studies conducted since the mid-1990s have lent additional support to the reaction network shown in Scheme 3.1 and emphasized the interesting class of heterogeneous-homogeneous radical nature of the system.539 Isotope labeling experiments have demonstrated that at small conversions levels most of the C02 is derived from methane, whereas at high conversion levels required for practical applications, ethylene is the dominant source of C02.543... 

Swann et al. [9] used isotopic labeling and temperature-programmed oxidation (TPO) (ex situ) approaches to show that the carbon which had formed during the C02 reforming of methane may have derived from both CH4 and C02. 

Cp 2Ln(CH3) is a remarkable compound. In the solid state, it is an unsymmetrical dimer (Figure 6.14), but in solution this is in equilibrium with the monomer. Monomeric Cp 2Ln(CH3) undergoes some remarkable reactions with inert substances, demonstrating a very high Lewis acidity. Thus it activates CH4, a reaction that can be followed using isotopically labelled methane. 

Studies of organoactinide surface chemistry and catalysis have been carried out by the Marks group under rigorously anhydrous/anaerobic conditions on either partially dehy-droxylated alumina (PDA) or DA at surface coverages of 0.25 0.50 molecules nm. The PDA and DA surfaces are represented schematically in equation (68). Product yields, isotopic labeling, and surface reactivity indicate that the irreversible y-alumina adsorption chemistry of Cp 2AnMe2 can be described by three methane-evolving pathways (equations 69-71). Equation (69) dominates on PDA. On DA,... 

Methanol reactions have also been studied on polycrystalline wafers of UO2 [76]. Two parent desorption states existed for methanol adsorbed at 90 K. Molecularly adsorbed methanol desorbed at 110 K, and methanol generated by surface recombination of methoxides and protons desorbed at 180 K. Carbon (Is) XPS demonstrated that methanol dissociatively adsorbed on the urania surface and that methoxide was the only surface intermediate present above 150 K. Primary reaction products were methane and carbon monoxide at 480 K. Oxygen atoms not removed from the surface as CO were incorporated into the oxide surface isotopically labeled U 02 surfaces did not exchange oxygen with methoxide to produce C 0 [76]. 

In summary the methane fermentation of H2 (Reaction 2) is the only example so far which unequivocally uses COo as a methane precursor, and it may be the only methanogenic component in most other substrate decompositions reported as methane fermentations. There are, however, two examples of methane fermentations where the major methane precursor is never COo but an intact methyl group. In the methane fermentations of acetate and methanol, isotopic labels of the methyl groups are transferred without loss or randomization of their hydrogen substituents, to methane ... 

Progress has also been achieved toward the direct oxidation of methane to acetic acid, for example, by Periana and coworkers, who used a Pd(II) catalyst in concentrated sulfuric acid at 180 °C [191-193]. The results of isotopic labeling experiments were consistent with a mechanism in which oxidation of methanol (from methane) generates a "CO" species that carbonylates a Pd-methyl species formed by C-H activation. 

Solution thermolysis of [PtIV(Me)2H(K3-Tp )] also induces reductive elimination of methane. C-D bond activation occurs after methane elimination in benzene-, to yield [PtIV(Me)(C6D5)D(k 3-Tp )] (Fig. 2.128), that upon a second reductive elimina-tion/oxidative addition reaction forms isotopically labeled methane and [PtIV(C6D5)2D(K3-Tp )]. [Pt(Me)(NCCD3)(K2-Tp )] has been obtained upon elimination of methane from [PtIV(Me)2H(K3-Tp )]. The a-methane complex [Ptn(Me)(K2-Tp )(CH4)] has been indicated... 

SCHEME 11.25 Isotopic labeling study to probe competition between methane dissociation (A diss) and methane C—H(D) activation ( ch) (Ar = 3,5-(CF3)2C6H3). 

The photolysis of benzobarrelene 7-A has been studied in considerable detail. Direct photolysis gives 7-C (benzocyclooctatetraene), but when acetone is used as a photosensitizer, the di-TT-methane rearrangement product 7-B (benzosemibullvalene) is formed. A deuterium-labeling study gave the results shown. What mechanistic conclusions do you draw from these results Is there a feasible mechanism that would have resulted in a different isotopic label distribution in 7-B ... 

Pachuta, S. J., and Strobel, M. "Time-of-Flight SIMS Analysis of Polypropylene Films Modified by Flame Treatments Using Isotopically Labeled Methane Fuel." Journal of Adhesion Science and Technology 21 (2007) 795-818. 

IN SSITKA, Np and the mean surface residence time of these most active reaction intermediates (xp) are determined. After a step-change between two reactant streams containing different isotopes of a reactant without disturbing other reaction conditions or reaction (as long as an H2/D2 switch is not used), the distributions of isotopically labeled products are monitored using a mass spectrometer. Tp is first determined by integration of the normalized isotopic transient of a product relative to an inert tracer (usually Ar) that delineates gas phase hold-up (see Figure 1 for the case of methanation). Np is then calculated from... 

Notable exceptions to this generalization, apart from the lack of activity towards derivatives of the phosphonic acids, are isopropyl- and / r/-butyl-phosphonic acids and ben-zylphosphonic acid (2-methylpropyl)phosphonic acid is cleaved to give very low yields of 2-methylpropene and 2-methylpropane Isotopically labelled (carbon or hydrogen) methylphosphonic acid affords methane possessing the identical distribution of the... 

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