Deuteration experiment

Tire infrared speetrum of l,5-diamino-l,2,4-triazolo[l,5-c]quinazolinium bromide (75) showed two intense absorptions near 1700 em Tliese absorptions were interpreted, on the basis of deuteration experiments, to be due to V C=N" eoupled with 8 NH2 and other ring modes [79JCS(P2)1708]. 

The proposed catalytic cycle is shown in Scheme 31. Hence, FeCl2 is reduced by magnesium and subsequently coordinates both to the 1,3-diene and a-olefin (I III). The oxidative coupling of the coordinated 1,3-diene and a-olefin yields the allyl alkyl iron(II) complex IV. Subsequently, the 7i-a rearrangement takes place (IV V). The syn-p-hydride elimination (Hz) gives the hydride complex VI from which the C-Hz bond in the 1,4-addition product is formed via reductive elimination with regeneration of the active species II to complete the catalytic cycle. Deuteration experiments support this mechanistic scenario (Scheme 32). 

Scheme 32 Deuteration experiment for 1,4-addition of a-olefins to diene catalyzed by an iminopyridine-ferrous chloride complex...

Furthermore, details of the isomerization of 1-aIkenes into 2-aUcenes were examined by deuteration experiments [177] and by using time-resolved IR spectroscopy in... 

Deuteration experiments suggested an intra- as well as an intermolecular migration of the acyl group. / -Methoxybenzoyl- and / -nitrobenzoylimidazole did not undergo acyl migration upon irradiation. Af-Crotyl- and TV-geranylimidazoles are stable to irradiation. 

Many research groups have attributed the isomerization to a series of additions and eliminations of a cobalt carbonyl hydride. However, it has been shown that aldehydes may be found with formyl groups attached to a carbon atom other than the two of the double bond even under non-isomerizing conditions. Piacenti and co-workers (44, 45) studied the hydroformylation of [l-14C]propylene and of a>-deuterated a-olefins. Even for a-olefins with chain lengths up to C6, the formyl group was attached to all possible carbon atoms in the product mixture. However, in the deuterated experiments, deuterium was present only on carbons 2, 3, and a) of the resulting aldehydes. These results were explained by pro-... 

With this background, the finding by Merck chemists [51] that unprotected dehydro / -amino acids are good substrates for the Rh-catalyzed hydrogenations was both very unexpected and very exciting. Interestingly, deuteration experiments indicate that it is not the enamine C=C bond which is reduced but the tautomeric imine Not only simple derivatives but also the complex intermediate for MK-0431 (see Fig. 37.10) can be hydrogenated successfully, and the latter has been pro-... 

The nature of the bonds between cellulosic fibres in paper has been the subject of some controversy over many years. The early and now largely discredited view was that paper derived its strength merely from mechanical entanglement of the fibres. However, experiments in which paper is formed from non-aqueous solvents produce sheets with very poor strength properties and have thus tended to disprove this conjecture. In the mid-1950s deuteration experiments were carried out which demonstrated that of the order of 0.4-2% of all hydroxy groups are additionally bonded in paper as compared with the unbonded fibres. This observation led to the view that... 

The representative points are derived from deuteration experiments carried out a potential located past the cyclic voltammetric peak potential. The compass rose on the top right summarizes the effect of the various rate and operational parameters. Adapted from Figure 1 in reference 39, with permissions from the American Chemical Society. 

The enantioselectivity is determined in an irreversible step after the chiral atom has been formed. Deuteration experiments have shown that styrene... 

Mechanism. The generally accepted mechanism for the hydrogenation of double bonds over heterogeneous catalysts was first proposed by Horiuti and Polanyi,50,51 and was later supported by results of deuteration experiments. It assumes that both hydrogen and alkene are bound to the catalyst surface. The hydrogen molecule undergoes dissociative adsorption [Eq. (11.1)], while the alkene adsorbs associa-tively [Eq. (11.2)]. Addition of hydrogen to the double bond occurs in a stepwise manner [Eqs (11.3) and (11.4)] ... 

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... 

Os(NH3)5(NCS)]2+ was first prepared by the reaction of [Os-(NH3)5(OH2) ]3+ with KSCN in water (197), and, more recently, by the reaction of [0s(NH3)5(0S02CF3)]2+ with NH4SCN in acetone (198). It undergoes a reversible reduction to the Os(II) complex and an irreversible oxidation to Os(IV). A complete analysis of the Raman and IR spectra (including deuteration experiments) has been reported, and the electronic spectra, including near-infrared bands, are discussed. [Os-(NH3)4(NCS)2]+ and [Os(NH3)3(NCS)3] are by-products of the reactions, but have not been characterized (198). 

The structure (64) has now been suggested, on the basis of NMR and deuteration experiments, and a reasonable mechanism formulated.260 The same mechanism (Scheme 17) explains the formation of the dimer of ageratochroinene with various acids.261 Iodine in acid-free chloroform yields instead the dimer (65).261... 

The major pathways for the fragmentation of kojic acid (81,5-hydroxy-2-hydroxymethyl-pyran-4-one), are shown in Scheme 14 support for each route was provided by the appearance of metastable ion peaks (67MI22203). An RDA cleavage followed by loss of a CH2OH radical produces ion (81a), m/e 69, the structure of which was substantiated by deuteration experiments. The ion at m/e 97 arises by extrusion of CO from the molecular ion and loss of HO- from the side chain structures (81b) and (81c) were proposed. Decomposition of [M]t occurs to give ethylene and an HC=0 fragment. The initial stage involves loss of a -CHO radical from the hydroxymethyl substituent, a process which has... 

The above authors rationalized formation of the more hindered i omer by assuming the equilibrium to be displaced in its favor by virtue of the lower solubility of this isomn relative to the other. House and Ho,885 on the other hand, showed by deuteration experiments and nuclear magnetic resonance spectroscopy that the epimeriza-tion observed by Washerman and oo-workera1Wfi IH0 proceeds by way of an unueual oxide anion in which negative charge resides on carbon as ehovra in Eq. (SS). 

The chemical shifts of the six protons in the rather complex H NMR spectrum of benzo[6]thiophenes have been estimated from specific deuteration experiments.83,87,89 The chemical shifts of H-5... 

The decline in optical rotation of the esters 2a and 2 b as a function of time is not affected by the addition of triphenylphosphine (Fig. 1). P(CgHs)3 in concentrations up to 10-fold excess with respect to complex concentration had no effect at all on the rate of racemization of 2a and 267. Deuteration experiments indicated that triphenylphosphine is indeed the ligand which dissociates. When the racemization of the manganese esters 2 is carried out in the presence of deuterated triphenylphosphine, P(C6D5)3 is incorporated into the complexes 16 [Eq. (14)]. A kinetic study showed that the rate of triphenylphosphine exchange is exactly equal to the rate of racemization8. ... 

Lygin and Kiselev42 proved by deuteration experiments that intraglobular hydroxyls are even not accessible to D20. Therefore, the surface modification of silica with HMDS (or with other chemical modifiers) is a typical probe of surface hydroxyl groups. 

Radical additions of primary, secondary, and tertiary alkyl bromides 249 to diethyl mesaconate 248 catalyzed by 5 mol% vitamin B12a 247 (X=OH2) proceeded in yields of 63-90% [301]. Deuteration experiments and comparison to similar addition processes support that 247 is initially reduced to cobalt complex 253A. This reacts with 249 giving an alkylcobalamin(III) intermediate... 

Hydropyridinyl radicals have given excellently resolved ESR spectra which have been assigned following MO calculations and partial deuteration experiments. Experimental results from various workers are compared in Table III for a series of C-monosubstituted 1-hydropyridinyl radicals. 

To resolve the question of the connection of spermine with the benzofuran system, the compounds 185 (Scheme 33) and 186 (Scheme 34) were prepared and analyzed. In 179 the units are connected by three bonds, two of which are amide bonds. One of the amides is N-monosubstituted and must therefore represent one end of the spermine unit. By treatment of 180 with benzoyl chloride this N-substituted amide is transformed to an N-sub-stituted secondary amid (imide), which under mild hydrolysis conditions [preferred cleavage of the N-23—C-24 bond] followed by esterification yielded 185. Deuteration experiments, transformation reactions with 185, as well as extensive spectroscopic investigations, have shown that in 179 N-23 is connected to C-24 and not to C-19. 

Early experiments with bacteriorhodopsin (228) interpreted the Raman spectrum in terms of an unprotonated Schiff base, forming a charge-transfer complex with a protein functional group (210,212). This interpretation of the Raman data, essentially based on a comparison with the frequencies of model Schiff bases in solution, was criticized by Honig and Ebrey (48), who pointed out that consistency could also be obtained with a protonated Schiff base model. The latter hypothesis was subsequently confirmed by deuteration experiments similar to those described for rhodopsin (229,230), and by Raman spectra in denatured systems (231). In variance with the clear-cut similarity observed between the resonance-Raman spectra of rhodopsin and isorhodopsin, and those of the 11-cis and 9-cis model compounds, respectively,... 

A one-pot conversion of alkenes to iV-methylaziridines has been achieved by aminopalladation followed by an oxidative woik-up with bromine (Scheme 15). The reaction is stereospecific, as shown by deuteration experiments, but has been little exploited. - 2-Aminopalladium compounds such as (21) are extremely versatile depending on starting compounds and work-up reagents, Aey can be made to yield a wide variety of products (Scheme 16). ... 

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