Isotopes exchange with solvent

The Bilik reaction applied to 2-ketoses yield 2-hydroxymethyl aldoses in which the tertiary carbon originates from C2 of the ketose and the C2 hydroxyl is on the opposite side to the C3 hydroxyl of the ketose (in the Fischer projection). Thus, o-fructose yield o-hamamelose. The position of equilibrium, however, lies towards the straight-chain sugar, although it can be pulled over somewhat towards the branched-chain aldose by the addition of borate. The mechanism in Figure 6.9 again explains the main reaction, but not the formation of sorbose as a by-product, which probably arises from a metal ion-promoted hydride shift, as there is no isotope exchange with solvent. The Bilik reaction can be applied to the production of l-deoxy-o-xylulose from 2-C-methyl-D-erythrose the reaction is particularly clean and only the two... 

Another example is the absence of oxygen exchange with solvent in the hydrolysis of gluconolactone. Simple acyclic esters usually undergo isotopic exchange at a rate that is conqietitive with hydrolysis. This occurs through the tetrahedral addition intermediate. 

Tetralin. Therefore, either trans-Decalin was formed on the surface of the coal with deuterium from the solvent or gas, or it was formed by isomerization from cis-Decalin with accompanying isotopic exchange with a deuterium source. Because the protium content of the cis-Decalins is much greater than the trans-Decalins, cis-trans isomerization is not very important. 

CH bonds in alpha position to carbonyl, sulfonyl, or nitro groups may undergo slow hydrogen isotope exchange with a hydroxylic solvent in the presence of a strong base. In another method of measurement of the deprotonation rate, a reagent (bromine or iodine) is added which reacts... 

Chemical studies also support the indicated mechanism. For example, the p-oxoacid intermediate formed in step h of Eq. 13-48 or Fig. 13-12 has been identified as a product released from the enzyme by acid denaturation during steady-state tumover. Isotopic exchange with in the solvent and measurement of C isotope effects have provided additional verification of the mechanism. TTie catalytic activity of the enzyme is determined by ionizable groups with piC values of 7.1 and 8.3 in the ES com-plex. ... 

One complication in the study of isotope effects is that there may be isotopic exchange with the solvent. For example, if we replace the alcoholic H atom in an alcohol ROH by D or T, and dissolve the product in ordinary water, there will be very rapid exchange of H and D or T atoms, the equilibrium... 

In solution, isotopic incorporation of deuterium from deuterated solvents into metal-bound hydrogen is common, e.g., reaction of acetone-reaction occurs between the Os complex and acetone even at reflux temperature thus the isotopic exchange with acetone-isotopic exchange may therefore occur via a deprotonation/reprotonation pathway coupled with a keto-enol tautomerization. 

Solutions of the salt K2PtCU in aqueous acetic acid are more stable upon heating than aqueous solutions. A 50% aqueous solution of acetic acid is very convenient to use as a solvent. Furthermore, in aqueous solutions, the solubility of hydrocarbons is rather low. Besides, even with a consideration of a different solubility of the hydrocarbons, the rate of alkane isotope exchange with D2O in 50% acetic acid turns out to be about 30 times greater than in water. Since a methyl group of acetic acid also exchanges with D2O in the presence of Pt(II), a... 

The kinetic data together with isotope exchange and solvent isotope elfect data are consistent with a mechanism involving non-interconverting cis and trans allylic carbanion intermediates, with partially intramolecular proton transfer,... 

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