Hydrogen/deuterium reaction with

The superacidic properties of trichlorogermane are clearly manifested in the properties of its etherates (vide infra) and the ability of DGeCl3 to participate in a deuterium-hydrogen exchange reaction with methylbenzenes32 (Section VIII.E). 

Eley-Rideal) mechanism, one of the reactants comes directly from the fluid phase to react with the other, which is already chemisorbed. This procedure was devised to explain the kinetics of the hydrogen-deuterium reaction on certain metals (see Section 9.2), but has also been suggested for other reactions. The Mars-van Krevelen mechanism applies to oxidations catalysed by oxides that are easily reducible, and are therefore able to release their lattice oxide ions for the purpose of oxidising the other reactant they are then replaced by the dissociation of molecular oxygen. With gold catalysts supported on such oxides, it is sometimes proposed that this mechanism plays a part in the total process. 

In support of this hypothesis it has been observed that when aluminum bromide is treated with oxygen a reaction occurs which liberates bromine,48 and further, the halogen atoms rather than the hydroxyl group are responsible for the catalytic activity of HOAlBr2. Thus when the compound DOAlBr2 is prepared, the hydrogen-deuterium exchange with n-butane is not at all proportional to isomerization.4 ... 

This chapter describes subsequent experiments to clarify the mechanism of reactions of alkanesulfonyl chlorides and related compounds with water, alcohols, and aromatic amines. In the course of these studies, we also noted a third-order term in the rate law and further work on this led to the observation of hydrogen-deuterium multiexchange with small tertiary amines. These results prompted further study, which has proceeded gradually over a number of years. The current state of this work is described. 

At 90° on a moderately active catalyst of nickel wire in the absence of ethylene the hydrogen-deuterium reaction is complete within 3 hrs. The presence of ethylene markedly retards the rate of this reaction as the following experiment showed 12 mm. of C2H4,9.6 mm. D2, and 10.1 mm. of H2 were contacted with the nickel wire for 4 hrs. At the end of this period, when 10% addition to the double bond took place, there were 6.1 mm. of D2,8.4 mm. H2, and 4.5 mm. HD. If equilibrium had been attained, the composition would be 4.0 mm. D2,6.0 mm. Hg, and 9.2 mm. HD, indicating that the ethylene had suppressed the equilibration of the hydrc en isotopes. 

The great advantage of the study of exchange reactions of isotopic molecules on catalysts is that only one molecular species is involved both as reactants and products. One is freed from the restrictions imposed with two reactants where the displacement of one reactant by another or by a reaction product must steadily be taken into consideration. The catalysts which reveal heterogeneity by desorption-readsorption studies should show the same variation in activation energy of reaction with temperature that Taylor and Smith found with zinc oxide in the hydrogen-deuterium reaction. Research in this direction is under way. 

Xi M and Bent B E 1993 Reaction of deuterium atoms with cyclohexane on Cu(111)—hydrogen abstraction reactions by Eley-Rideal mechanisms J. Phys. Chem. 97 4167... 

Azaindolizine, 5-chloro-nucleophilic substitution, 4, 458 8-Azaindolizine, 7-chloro-nucleophilic substitution, 4, 458 Azaindolizines basicity, 4, 454 electronic spectra, 4, 445 electrophilic substitution, 4, 453 halogenation, 4, 457 hydrogen/deuterium exchange, 4, 458 NMR, 4, 447, 449 nucleophilic attack, 4, 458 protonation, 4, 453 reaction with isothiocyanates, 4, 513 reactions, 5, 267 reviews, 4, 444 UV spectra, 4, 446, 449 Azaindolizines, amino-tautomerism, 4, 452... 

Aliphatic sulfonyl chlorides that have a-hydrogen substituents, react with simple tertiary amines, such as trimethylamine, to generate sulfenes or perhaps their amine adducts 446). These species are suggested by the incorporation of one (but not more) deuterium atoms on reaction of sulfonyl chlorides with deuterated alcohols and triethylamine (447-450). A 2 1 adduct of sulfene and trimethylamine with proposed sulfonyl-sulfene structure could be isolated (451). 

The Diels-Alder reaction of a diene with a substituted olefinic dienophile, e.g. 2, 4, 8, or 12, can go through two geometrically different transition states. With a diene that bears a substituent as a stereochemical marker (any substituent other than hydrogen deuterium will suffice ) at C-1 (e.g. 11a) or substituents at C-1 and C-4 (e.g. 5, 6, 7), the two different transition states lead to diastereomeric products, which differ in the relative configuration at the stereogenic centers connected by the newly formed cr-bonds. The respective transition state as well as the resulting product is termed with the prefix endo or exo. For example, when cyclopentadiene 5 is treated with acrylic acid 15, the cw fo-product 16 and the exo-product 17 can be formed. Formation of the cw fo-product 16 is kinetically favored by secondary orbital interactions (endo rule or Alder rule) Under kinetically controlled conditions it is the major product, and the thermodynamically more stable cxo-product 17 is formed in minor amounts only. 

On the basis of these correlations, Gold and Satchell463 argued that the A-l mechanism must apply (see p. 4). However, a difficulty arises for the hydrogen exchange reaction because of the symmetrical reaction path which would mean that the slow step of the forward reaction [equilibrium (2) with E and X = H] would have to be a fast step [equivalent to equilibrium (1) with E and X = H] for the reverse reaction, and hence an impossible contradiction. Consequently, additional steps in the mechanism were proposed such that the initial fast equilibrium formed a 7t-complex, and that the hydrogen and deuterium atoms exchange positions in this jr-complex in two slow steps via the formation of a a-complex finally, in another fast equilibrium the deuterium atom is lost, viz. 

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