Intramolecular hydrogen-deuterium exchange

Of interest also is the intramolecular hydrogen-deuterium exchange invoked to explain the reactions depicted in equation [93] (262). Reactions of complexes 174 and 175 led to an equimolar mixture of complexes 176 and 177 indicating that these two compounds are in equilibrium. An intermolecular exchange has been rejected on the basis of the findings shown in equation [94]. The above exchange thus occurs within the coordination sphere of manganese and does not involve formation of free hydrosilane by a reductive elimination process. The... 

Of interest also is the intramolecular hydrogen-deuterium exchange invoked to explain the reactions depicted in equation 1978. The reactions of hydrido and deuterio... 

Hittle, L.R., Proctor, A., and Hercules, D.M., Investigation of intramolecular hydrogen-deuterium exchange in the time-of-flight secondary-ion mass spectra of polystyrene. Macromolecules, 28, 6238, 1995. 

A large number of papers related to this subject has been published since then, which can be classified into three types of mechanistic approaches (i) studies of initial product distribution, (ii) hydrogen deuterium exchange studies and (iii) theoretical calculations. In this review we will limit ourselves essentially to H/D isotope exchange studies between the acidic catalyst and small alkanes. In most cases, it is possible to observe inter-molecular H/D exchange in the absence of side reactions such as intramolecular atom scrambling, isomerisation or cracking. 

Kim, M.Y., Maier, C.S., Reed, D.J., et al. (2001) Intramolecular interactions in chemically modified Escherichia coli thioredoxin monitored by hydrogen/deuterium exchange and electrospray ionization mass spectrometry. Biochemistry, 40 (48), 14413-14421. 

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 ... 

The effect of temperature is peculiar (see Fig. 13). The deuterium content of the reactant olefin, in this case 1-butene, at about 10% conversion falls with increasing temperature, paralleling its behavior in isomerization. However, the deuterium content of the isomerized 2-butenes rises rapidly, as does also the deuterium number of the butane. This tells us (1) intramolecular hydrogen transfer becomes less important with rising temperature and is perhaps replaced by reactions involving adsorbed deuterium atoms (step 1. ii), and (2) butane is probably formed through the same intermediates as those which yield 2-butenes, viz., 2-butyI radicals. The same kind of behavior is shown by the other butenes. Partial pressure variation has no remarkable effect on the course of exchange and isomerization. 

X (D)], where n is the number of intervening bonds between the deuterium and the observed nucleus, X . The most studied of these effects is the two-bond isotope effect on chemical shifts, AC(XD), produced upon H/D exchange at XH. This isotope effect has been correlated with d(XH) and, when XH takes part in an intramolecular hydrogen bond, to the hydrogen-bond enthalpy The magnitude of... 

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