Deuterium exchange, determination

Each act of proton abstraction from the a carbon converts a chiral molecule to an achi ral enol or enolate ion The sp hybridized carbon that is the chirality center m the start mg ketone becomes sp hybridized m the enol or enolate Careful kinetic studies have established that the rate of loss of optical activity of sec butyl phenyl ketone is equal to Its rate of hydrogen-deuterium exchange its rate of brommation and its rate of lodma tion In each case the rate determining step is conversion of the starting ketone to the enol or enolate anion... 

The hydrogen-deuterium exchange rates for 1,2-dimethylpyrazolium cation (protons 3 and 5 exchange faster than proton 4 Section 4.04.2.1.7(iii)) have been examined theoretically within the framework of the CNDO/2 approximation (73T3469). The final conclusion is that the relative reactivities of isomeric positions in the pyrazolium series are determined essentially by inductive and hybridization effects. 

Oosterhuis WT (1974) The Electronic State of Iron in Some Natural Iron Compounds Determination by Mossbauer and ESR Spectroscopy. 20 59-99 Orchin M, Bollinger DM (1975) Hydrogen-Deuterium Exchange in Aromatic Compounds. 23 167-193... 

Deuterium exchange with DjO was used by Shuravlev and Kiselev (199) in the determination of surface hydroxyl groups of silica gel. Adsorption isotherms of HgO and DjO were determined gravi-metrically they agreed with each other within the limits of experimental error. 

Woods, V.L. Jr. Hamuro, Y High resolution, high-throughput amide deuterium exchange-mass spectrometry (DXMS) determination of protein binding site structure and... 

In the aqueous pH region the mechanism for hydrogen-deuterium exchange in pyridine involves attack of deuteroxide ion on the pyridin-ium ion to give an ylide intermediate (Scheme 8). The ylide then reacts with D2O to give the deuterated p30 idine. In more basic media the proposed mechanism involves rate-determining deprotonation from the neutral molecule to give a carbanion intermediate which then abstracts a deuteron from the solvent (Scheme 9). 

Ring protons of 1,2,3-thiadiazoles are known to undergo rapid deuterium exchange under basic conditions, yet to date there have been no published estimates or experiments to determine the pA of these protons. Few attempts have even been made to metalate and alkylate this heterocycle. One study <85S945> found that metalation of 5-phenyl-1,2,3-thiadiazole (25) with methyllithium gives 4-lithio-5-phenyl-l,2,3-thiadiazole, which is stable and reacts with aldehydes and ketones in high yields (Equation (11)). Also, treatment of 4-phenyl-1,2,3-thiadiazole with lithium diisopropylamide, in the presence of TMS-Cl, affords 4-phenyl-5-trimethylsilyl-1,2,3-thiadiazole. 

Figure 5. Relative acidity of a-protons as determined by the conformational effect of deuterium exchange on a conformationally biased system...

N- Methylbenzodihydroazocines (83), (84), and (85) have been studied from the standpoint of possible stabilization of the IOtt- electron anions available by deprotonation (71JA4016). The kinetic acidities, determined by deuterium exchange rates, indicate that (83) and (84) are converted to the anions about 80 and 30 times faster, respectively, than the corresponding 1,2- and 1,4-dihydroquinoline models the enhancement in (85) was slight. By this criterion the benzazocinyl anion (86) was judged to have some degree of aromatic character. 

It has been concluded from deuterium exchange experiments, using ethylene and heavy water, that the addition of an adsorbed proton to adsorbed ethylene is the actual rate-determining step. It can be seen that the two schemes differ, mainly in that the latter includes dissociative adsorption of water on the surface of the catalyst and does not specify the adsorption of ethylene, but they are consistent in that they assume the formation of a carbonium ion as the rate-determining step. 

Since acetonaphthones have 7r,7r configurations in their lowest triplet states, it seems probable that l-benzoyl-2-methylnaphthalene, 30, would also. As suspected, 30 does not undergo photoenolization.362 However, 6-benzoylbenzanthrone, 31, which would also be expected to possess a low-lying triplet, does form a photoenol, as determined by formation of yellow coloration at low temperatures and deuterium exchange at the benzylic position. It is entirely possible that the greater reactivity of the benzyhydryl C—H bond in 31 allows reaction even in a relatively unreactive state, or in an n,tt singlet. 

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