Deuteration/deuterium

Both 3-amino- and 3,4-diaminothiophene exhibit enaminic character. On acid-catalyzed deuteration, deuterium enters the thiophene a-positions. However, a detailed potentiometric as well as H NMR study of the protonation of 3,4-diaminothiophene has revealed that both monoprotonation as well as diprotonation occurs on the nitrogen atoms (Scheme 68) (93JOC4696). The pvalues in 50% DMSO - water mixture are 3.96 and 0.98. 

The reactions of these octalins with deuterium, to yield deuterated cis- and irowa-decalins, has also been investigated (14). In each case the exchange rate is 10-20 times slower than the rate of addition, and deuterium contents of the two decalins are about the same. However, the decalins formed from d -octalin were the more extensively deuterated (deuterium contents at 55% conversion, 2.85, 2.85 at 37% conversion, 2.02, 1.83). Hydrogen exchange was apparent during the reaction of d -octalin but not with the d -octalin. A theoretical scheme was developed to interpret the distributions of the deuterated decalins, the tails of which decline in the familiar logarithmic manner (see Fig. 16). 

Heavy hydrogen or deuterium is used to deuterate compounds and correlate the changes in their near-infrared spectral band positions, intensities, and widths for both the deuterated (deuterium-labeled) and undeuterated (unlabeled) molecules. This experiment provides information for the... 

However, when 5 was lithiated with BuLi and then deuterated, deuterium incorporation occurred with a preference of ca. 2 1 for the C-6 position. Lack of the desired regioselectivity for the C-S in this reaction led us to develop another route to S-substituted uridines. As the C-5 position is alpha to the carbonyl group, we expected that saturation of the 5,6-double bond would provide an "amide a-anion" despite the presence of the acidic N3-H. 

Two of the most important functions in the application of neutron scattering are the use of deuterium labelling for the study of molecular confomiation in the bulk state and the use of deuterium solvent in polymer solutions. In the following, we will consider several different applications of die general fomuda to deuteration. 

Radiolabeled folate provides a powerful tool for folate bioavaHabiUty studies in animals and for diagnostic procedures in humans. Deuteration at the 3- and 5-positions of the central benzene ring of foHc acid (31) was accompHshed by catalytic debromination (47,48) or acid-cataly2ed exchange reaction (49). Alternatively, deuterium-labeled fohc acid (32) was prepared by condensing pteroic acid with commercially available labeled glutamic acid (50). 

In pyridazine, base-catalyzed hydrogen-deuterium exchange takes place at positions 4 and 5 more easily than at positions 3 or 6. Deuteration of pyridazine 1-oxide in NaOD/DiO... 

In theory two carbanions, (189) and (190), can be formed by deprotonation of 3,5-dimethylisoxazole with a strong base. On the basis of MINDO/2 calculations for these two carbanions, the heat of formation of (189) is calculated to be about 33 kJ moF smaller than that of (190), and the carbanion (189) is thermodynamically more stable than the carbanion (190). The calculation is supported by the deuterium exchange reaction of 3,5-dimethylisoxazole with sodium methoxide in deuterated methanol. The rate of deuterium exchange of the 5-methyl protons is about 280 times faster than that of the 3-methyl protons (AAF = 13.0 kJ moF at room temperature) and its activation energy is about 121 kJ moF These results indicate that the methyl groups of 3,5-dimethylisoxazole are much less reactive than the methyl group of 2-methylpyridine and 2-methylquinoline, whose activation energies under the same reaction conditions were reported to be 105 and 88 kJ moF respectively (79H(12)1343). 

Intermolecular reactions with typical cycloaddition components are also possible. Phenyl isocyanate in ether converts triisopropyldiaziridinimine (182) to the 1,2,4-triazolidine under mild conditions. Labeling with a deuterated isopropyl group revealed that cycloaddition is not preceded by N—N cleavage, which should have resulted in deuterium randomization (77AG(E)109). 

With more strongly basic tertiary amines such as triethylamine, another mechanism can come into play. It has been found that wften methanol deuterated on oxygen reacts with acyl chlorides in the presence of triethylamine, some deuterium is found a to the carbonyl group in the ester... 

Further evidence for a bromine-bridged radical comes from radical substitution of optically active 2-bromobutane. Most of the 2,3-dibromobutane which is formed is racemic, indicating that the stereogenic center is involved in the reaction. A bridged intermediate that can react at either carbon can explain the racemization. When the 3-deuterated reagent is used, it can be shown that the hydrogen (or deuterium) that is abstracted is replaced by bromine with retention of stereochemistry These results are also consistent with a bridged bromine radical. 

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 ... 

Fig. I. Block copolymers tend to organise at an interface so that the two blocks, shown here as solid and dashed lines, are on either side of the interface. If one of the blocks is deuterated then chain pull-out can be distinguished from chain scission by the location of the deuterium on the fracture surface.

This process accounts for most of the observations relating to product stereochemistry, double bond isomerism, deuterium exchange and other features encountered in the hydrogenation and deuteration of olefins. 140-142,144 addition of hydrogen to the double bond proceeds in... 

Complete exchange of protons in a sterically unhindered position a to a carbonyl group can be achieved by heating a solution of the ketone in O-deuterated solvents in the presence of an acid or base catalyst, the latter being the more effective. The most commonly used solvents are methanol-OD, ethanol-OD, and the aprotic solvent anhydrous tetrahydrofuran or dioxane mixed with deuterium oxide. Under alkaline conditions the exchange rate in 153 2 14,164 stcroids, for example, is usually... 

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