Deuterium quenching

Because it was not possible to explain the differences in the effectiveness of hydrogen as compared to other gases on the basis of differences in their physical properties, ie, thermal conductivity, diffusivity, or heat capacity differences, their chemical properties were explored. To differentiate between the hydrogen atoms in the C2H2 molecules and those injected as the quench, deuterium gas was used as the quench. The data showed that although 90% of the acetylene was recovered, over 99% of the acetylene molecules had exchanged atoms with the deuterium quench to form C2HD and... 

It was predicted, a priori, that isocomene could be formed simply by treating 4 with methyllithium, followed by exposure of the resultant tertiary carbinol to acid.2b However, many attempts to effect the addition of a variety of nucleophilic methyl derivatives to ketone 4 were unsuccessful. It was revealed by deuterium quenching experiments that ketone 4 undergoes ready enolization in the presence of nucleophilic methyl derivatives. Despite its hindered nature, however, the ketone carbonyl in 4 reacts with methylenetri-... 

More recently, Landis et al. studied the polymerisation kinetics of 1-hexene with (EBI)ZrMe( t-Me)B(C5F5)3 64 as catalyst in toluene [EBI = rac-C2H4(Ind)2]. Catalyst initiation was defined as the first insertion of monomer into the Zr-Me bond, 65 (Scheme 8.30). Deuterium quenching with MeOD was used to determine the number of catalytically active sites by NMR. The time dependence of the deuterium label in the polymer was taken as a measure of the rate of catalyst initiation. This method also provides information of the type of bonding of the growing polymer chain to zirconium, as n-or sec-alkyl, allyl etc. Hexene polymerisation is comparatively slow, with high regio- and stereoselectivity there was no accumulation of secondary zirconium alkyls as dormant states [96]. 

Hughes and co-workers " studied the lithiation of 5-(3-methyl-5-isoxazolyl) oxazole 891 as part of their program to prepare suitable species for cross-coupling reactions (Scheme 1.239). They investigated the equilibrium of the 2-lithiooxazole 892 and the acyclic isocyanovinyUithium alkoxide 893 using H-NMR and C-NMR spectroscopy. The authors concluded that 893 was the predominant species under the reaction conditions investigated based on comparison of the H-NMR and C-NMR spectra with the spectra of 894 together with an extensive series of deuterium quenches. However, they also cautioned that the results of deuterium quenches of systems where dynamic equilibria are possible or expected must be interpreted with care. ... 

However, the optical train illustrated in Figure 22B allows the determination of fluorescence quenching. The interfering effect described above now becomes the major effect and determines the result obtained. For this purpose the deuterium lamp is replaced by a mercury vapor lamp, whose short-wavelength emission line (2 = 254 nm) excites the luminescence indicator in the layer. Since the radiation intensity is now much greater than was the case for the deuterium lamp, the fluorescence emitted by the indicator is also much more intense and is, thus, readily measured. 

Unlike the parent system, 5-methyl-5//-dibenz[c,e]azepine (1, R1 = Me R2 = H) on treatment with lithium diisopropyl amide fails to yield the tautomeric phenanthridine-imine (see Section 3.2.1.5.4.2.), but forms the 5-carbanion, which on quenching with deuterium oxide furnishes 5-methyl-[5-2H,]-5//-dibenz[e,e]azepine (l).83 5,7-Diphenyl-5//-dibenz[r,e]azepine (1. R1 = R2 = Ph) behaves similarly. In contrast, however, 5,7-dimethyl-5//-dibcnz[c,e]azepine (1, R1 = R2 = Me) yields theazaallyl anion 3, which on addition of deuterium oxide deuterates regiospecifically at the 7-methyl group to give derivative 4. 

Prolonged treatment (20 h) of 5//-dibenz[6,/]azepine (5, R1 = H) with an excess of butyllithium, followed by quenching into deuterium oxide, furnishes [4,6-2H2]-5//-dibcnz[6,/]azepine (rap 195-197 C) in 93% yield.47... 

The results of this study are presented in Table 4.7. As can be seen from the data in Table 4.7, decarbonylation with hydrogen or deuterium transfer to the resulting radical is a relatively efficient process. The failure to observe this reaction using acetone or acetophenone as photosensitizer would suggest a singlet pathway for the direct photolysis of the aldehyde. In agreement, decarbonylation could not be quenched by naphthalene, piperylene, or 1,3-cyclohexadiene when the aldehyde was excited directly. The reaction could, however, be somewhat quenched by the addition of tri-n-butylstannane. The products in this case were... 

Let us now discuss some of the characteristics of this quenching with mercaptans and disulfides. Interestingly, both sulfur derivatives are equally effective in inhibiting the photoreduction and are in fact interconverted during the reaction. The same equilibrium mixture of mercaptan and disulfide is obtained regardless of which was initially added to the reaction mixture. Furthermore, there appears to be no appreciable consumption of the sulfur compounds/64 When benzophenone is irradiated in the presence of isopropanol (OD) and mercaptan, isopropanol containing two deuterium atoms is isolated,... 

The stereochemistry of dienes has been found to have a pronounced effect in the concerted cyclo-additions with benzyne 64>65h A concerted disrotatory cyclo-addition of tetrafluorobenzyne, leading for example with trans- (3-methylstyrene to (63, R = Me), is likely and in accord with the conservation of orbital symmetry 68>. However while the electro-cyclic rearrangement of (63, R = H) to (65, R = H) is not allowed, base catalysed prototropic rearrangement is possible. A carbanion (64, R = H) cannot have more than a transient existence in the reaction of tetrafluorobenzyne with styrene because no deuterium incorporation in (65) was detected when either the reaction mixture was quenched with deuterium oxide or when the reaction was conducted in the presence of a ten molar excess of deuteriopentafluorobenzene. 

When we allowed pentafluorophenyl-lithium to decompose in ether in the presence of an excess of N, ZV-dimethy laniline we obtained the compounds (92) 70, X = F), (94), the latter as the major compound, and a product which was shown to be (97). That this latter compound did not arise by metallation of 2V,lV-dimethylaniline followed by addition to tetrafluorobenzyne was shown by quenching the reaction mixture with deuterium oxide. No deuterium incorporation was detected. The compound (97) provides a rare example of a product derived by a Stevens rearrangement in which aryl migration has occurred b>. 

The fluorescence is not quenched by pyridine (i.e., the excited diazirines do not react with pyridine), although the carbenes do react with pyridine to form ylides. Importandy, the fluorescence from diazirine 35-dt is 50% stronger than that of 35, and the pyridine-trappable yield of carbene 36-dt (from 35-df) is 50% greater than that of 36 from diazirine 35. These results parallel deuterium kinetic isotope effects on RIES.22... 

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