Hydrogen rapid exchange with deuterium

The next coenzyme for which a mechanism was established was thiamin pyrophosphate [3]. Ronald Breslow used nmr spectroscopy to show that the hydrogen atom at C-2 of a thiazolium salt rapidly exchanges with deuterium in even slightly alkaline solutions (6), so that the coenzyme offers an anionic centre for catalysis (Breslow, 1957). With this established, Breslow could confidently offer the pathway shown in Scheme 2 for the action of the... 

The efficiency of reduction of benzophenone derivatives is greatly diminished when an ortho alkyl substituent is present because a new photoreaction, intramolecular hydrogen-atom abstraction, then becomes the dominant process. The abstraction takes place from the benzylic position on the adjacent alkyl chain, giving an unstable enol that can revert to the original benzophenone without photoreduction. This process is known as photoenolization Photoenolization can be detected, even though no net transformation of the reactant occurs, by photolysis in deuterated hydroxylic solvents. The proton of the enolic hydroxyl is rapidly exchanged with solvent, so deuterium is introduced at the benzylic position. Deuterium is also introduced if the enol is protonated at the benzylic carbon by solvent ... 

When treated with aluminum chloride in refluxing hexane, perhydrotriquinacene was rapidly isomerized to adamantane.382 Exposure of 1-, exo-2, or endo-2-per-hydrotriquinacenol to fluorosulfonic acid, followed by aqueous quenching, has been shown to produce 1-adamantanol. McKervey and his co-workers have found that 358 exchanges ten hydrogen atoms when subjected to exchange with deuterium and palladium.385 On this basis, the prediction was made that olefin 409 (presently an unknown molecule) should be a compound of moderate stability. 

However, fi adsorption on catalysts is also supported by deuterium exchange studies of thiophene. When thiophene and D2 are passed over Mo-based HDS catalysts at temperatures below which substantial HDS occurs, the thiophene protons exchange with deuterium. This exchange occurs much more rapidly at the 2- and 5-positions than at the 3- and 4-sites. When CpRu(jj -T)+ (equation 9) is dissolved in CD3OD in the presence of OD at 23 °C, the 2,5-hydrogens of thiophene... 

Hydrogen donors labelled with deuterium, such as tetralin-and naphthalene-4 have also been used to study the reaction mechanism of the hydrogen transfer. Tetralin-(ii2 is rapidly substituted in the 1-position by hydrogen from coal. At a reaction temperature of 400 °C the deuterium content of the 1-position remains, after a reaction time of 15 min, relatively constant at 66%. The 2-position, however, participates much less in the exchange reaction. On the other hand, the deu-... 

The substrate molecules may become labeled with deuterium by rapid hydrogen exchange, and then the newly labeled molecule may become cleaved in the rate-determining step. 

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