For exchange of deuterium

It is probable, then, that the activated complex for exchange of deuterium with water contains deuterium, hydroxyl ion, and possibly water molecules. Wirtz and Bonhoeffer had suggested the following two-step mechanism ... 

This process, invented by Spevack [S7) and developed independently by Geib [C2] in Germany, makes use of the fact that the separation factor a for exchange of deuterium between liquid water and gaseous hydrogen sulfide,... 

Only within the past few years have serious attempts been made to estimate quantitatively the differences in reactivity between thiophene and benzene and between the 2- and 3-position of thiophene. Careful investigation on the acid-induced exchange of deuterium and tritium have shown that the ratios of the exchange rates in the 2- and 3-positions are 1045 61 for deuterium and 911 60 for tritium in 57% by weight aqueous sulfuric acid at 24.6°C. A kinetic isotope effect in the isotopic exchange has been found to be k-r/kr, = 0.51 0.03 in the 2-position and kr/kjy — 0.59 0.04 in the... 

The observation of a primary solvent deuterium isotope effect (kH/fa>) = 2-4 on the specific acid-catalyzed hydrolysis of vinyl ethers provides evidence for reaction by rate-determining protonation of the alkene.69 Values of kHikD 1 are expected if alkene hydration proceeds by rate-determining addition of solvent to an oxocarbenium ion intermediate, since there is no motion of a solvent hydron at the transition state for this step. However, in the latter case, determination of the solvent isotope effect on the reaction of the fully protonated substrate is complicated by the competing exchange of deuterium from solvent into substrate (see above). 

For the exchange of deuterium with most saturated hydrocarbons (Anderson, 123) ... 

The extent of retention of tritium is 79 + 2 % in the former case and 21 2 % in the latter 155) complete retention (or complete loss) of tritium is, of course, not to be expected, since the isotope effect for extrusion of deuterium rather than protium in the condensation shown in Fig. 68 is not infinite. The percent tritium retention in the process of dehydration and water exchange (fig. 58) is now generally called the F-value 1491 thus enantiomerically pure CHDTC02H gives an F-value of either 79 (R configuration) or 21 (S configuration) values below 79 or above 21, i.e. closer to 50, indicate that the acid is not enantiomerically pure. The F-value determination... 

A quinone methide makes a surprising appearance as an intermediate of the photochemical exchange of deuterium from D20 into the 2 -position of 2-phenylphenol (13).27 29 No photochemical deuterium exchange is observed for reactions of the related phenylanisole 10 or phenylphenols 11 and 12, and deuterium exchange at the 4 -phenyl position of 13 is very much slower than... 

Polak and Molenaar described a method for the determination of acetylcholine from brain tissue by pyrolysis-gas chromatography-mass spectrometry [200]. The deuterium-labeled acetyl-choline is pyrolytically demethylated with sodium benzenethiolate, followed by quantitative GC-MS analysis. In this method, care must be taken so that the samples do not contain appreciable amounts of choline since exchange of deuterium-labeled groups between acetylcholine and choline during pyrolysis may yield erroneous results. The same authors have also reported a method for the determination of acetylcholine by slow pyrolysis combined with mass fragment analysis on a packed capillary column [201]. 

The deuterated anions of 7,8-isomer 9,11 -dideuterio-, 5,6,9,10,11-pentadeuterio- and 1,5,6,9,10,1 l-hexadeuterio-7,8-dicarba- developed method of selective isotope exchange of deuterium for hydrogen in 7,8-dicarba-nido-undecaborate(l-) with D20 at acidic conditions.12 Since terminal hydrogen atoms are not exchanged in basic media, the deuterium label proved to be quite useful for "B NMR studies of deuterium distribution in the rearrangement products. 

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