Butene, deuteration

As discussed previously, this reaction was also run under these same conditions over the series of specifically cleaved platinum single erystals shown in Fig. 3.2. 3 The results of these experiments show that it was the corner atoms on these crystals that promoted C-H bond breaking. Thus, the saturation sites on the dispersed metal catalysts are also comer atoms. Since this saturation site description agrees with that proposed on the basis of the butene deuteration described previously,5 -62 it is likely that the isomerization sites, M, are edge atoms and the hydrogenation inactive sites, M, are face atoms. A similar approach can be used to determine the nature of the active sites responsible for promoting almost any type of reaction. 5.70... 

Polymer (B) poly(ethylene-co-l-butene), deuterated 2008KO... 

Selectivities to various isomers are more difficult to predict when metal oxides are used as catalysts. ZnO preferentially produced 79% 1-butene and several percent of i7j -2-butene [624-64-6] (75). CdO catalyst produced 55% 1-butene and 45% i7j -2-butene. It was also reported that while interconversion between 1-butene and i7j -2-butene was quite facile on CdO, cis—trans isomeri2ation was slow. This was attributed to the presence of a TT-aHyl anion intermediate (76). High i7j -2-butene selectivities were obtained with molybdenum carbonyl encapsulated in 2eohtes (77). On the other hand, deuteration using H1O2 catalyst produced predominantly the 1,4-addition product, trans-2-huX.en.e-d2 with no isotope scrambling (78). 

The r/zreo-3-deutero-2-trimethylstannylbutane that Hannon and Traylor158 used to determine the stereochemistry of the hydride transfer reaction and to shed light on the mechanism of this reaction was synthesized using the reactions in Scheme 22. Each of the reactions in Scheme 22 is stereo specific and the analysis showed that the product was at least 97% r/rreo-3-deutero-2-trimethylstannylbutane. If the elimination reaction from t/zreo-3-deutero-2-trimethylstannylbutane occurs with an awh -periplanar stereochemistry, the products shown in Scheme 23 will be obtained. Thus, if the elimination occurs by an awft -periplanar stereochemistry, all the fraws-2-butene will be monodeuterated while the ds-2-butene will not be deuterated. A syw-periplanar elimination from f/zreo-3-deutero-2-trimethylstannylbutane, on the other hand, would give the products shown in Scheme 24. If this occurs, the cw-2-butene will contain one deuterium atom and the fraws-2-butene will contain none. 

The results of a mass spectrometric investigation of the products, after correcting for the 13 C content and the M-l fractionation of the molecular ion, showed that the trans-2-butene was > 97% deuterated and that less than 1% of the c -2-butene was deuterated. This means that at least 97% of the elimination reaction to form the fraws-2-butene and > 99% of the elimination to form the cw-2-butene occurred by an awh -periplanar mechanism (Scheme 23). 

The results from these experiments also allowed Hannon and Traylor to determine the primary and secondary hydrogen deuterium kinetic isotope effects for the hydride abstraction reaction. If one assumes that there is no kinetic isotope effect associated with the formation of 3-deutero-l-butene, i.e. that CH2=CHCHDCH3 is formed at the same rate (k ) from both the deuterated and undeuterated substrate (Scheme 25), then one can obtain both the primary (where a deuteride ion is abstracted) and the secondary deuterium... 

The primary hydrogen-deuterium kinetic isotope effect is obtained from the percent cw-2-butene obtained from the deuterated and undeuterated stannanes. This is possible because a hydride and a deuteride are transferred to the carbocation when the undeuterated and deuterated stannane, respectively, forms c -2-butene. The secondary deuterium kinetic isotope effect for the hydride transfer reaction is obtained from the relative amounts of fraws-2-butene in each reaction. This is because a hydride is transferred from a deuterated and undeuterated stannane when trans-2-butene is formed. 

Direct experimental evidence for the trans elimination in E2 reactions has been obtained from deuterated -2-bromobutane (the deuterium atom occupies position 3). This compound on dehydrobromination forms trans and cis butene-2 in the ratio of 6 1... 

The use of several different experimental techniques to investigate a given system is likely to be particularly revealing. Two noteworthy examples in which stereochemical considerations had a part are provided by Taylor and Dibeler (8) on the reactions of deuterium with the butenes on nickel wires and by Meyer and Burwell (9, 10) on the deuteration of multiply unsaturated hydrocarbons. 

The proportion of products obtained from 1,2-butadiene are 0.53 cis-2-butene, 0.07 Jrarts-2-butene, and 0.40 1-butene. The predominant deuterated species are again those which result from simple 1,2 addition to one or the other double bond. However 1-butene is more extensively exchanged than cis-2-butene. 

Nonconjugated dienes, namely, allenes and isolated dienes, react preferentially on the terminal double bond.10 Hydrogenation of 1,2-butadiene over palladium yields 1-butene and d.s-2-butene as the main products with moderate discrimination of the two double bonds.68 Deuteration experiments indicated that the dominant syn addition to either the 1,2- or the 2,3-olefinic bond occurs. Different vinyl and Jt-allyl intermediates were invoked to interpret the results.69 70... 

Cpsymmetric organolanthanide complexes exhibit moderate to good enantioselectivities in the hydrogenation and deuteration of styrene and 2-phenyl-1-butene.433 Cationic iridium-phosphanodihydrooxazole complexes are more efficient catalysts for the asymmetric hydrogenation of unfunctionalized aryl-substituted alkenes. The best catalyst (42) gives high yield (>99%) and excellent enantioselectivity (97% ee) in the hydrogenation of ( )-l,2-diphenyl-l-propene 434... 

C NMR spectra of poly(3-methyl-1-butene) and poly(4-methyl-1-pentene) were determined with a Varian CFT-20 spectrometer operated at ambient probe temperature ( 35° C) using 20-30% solutions of polymer in deuterated chloroform. Spectra were obtained utilizing off-resonance coupling and white noise decoupling techniques for both poly(3-methyl-l-butene) and poly(4-methyl-l-pentene). 

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