Hydrogen origin

It has been revealed that the formation of protonic acid sites from molecular hydrogen is observable for the catalysts other than Pt/S042--Zr02, and the protonic acid sites thus formed act as catalytically active sites for acid-catalyzed reaction. We propose the concept "molecular hydrogen-originated protonic acid site" as a widely applicable active sites for solid acid catalysts. 

Hydrogenation Temperature (°) Hydrogenation (Original Mol. Reaction Time (hr.) of Polybutadiene. Wt. = 209,000) Mn (Osmometry) % Chain Scission ... 

Hadler 26) employed conformational analysis to explain the difference in the proportion of cholestane to coprostane derivatives resulting from the reduction of A and d steroids. He suggested that the hydrogenation process involved the formation of a quasi-ring structure between the unsaturated carbon atoms and two hydrogens originally dissolved in the metal, a mechanism which is similar to one proposed by Beeck (27) and by Jenkins and Rideal 28). He assumed, in effect, that the saturated struc-... 

Fig. 12.81. Accumulated hydrogen (originating in electrochemical formation at the surface) produces cracks inside a metal. When it is strained, the metal fractures along the cracks rather than yielding. It has become brittle.

Figure 4. Changes of the transmission of 645 nm light through the film deposited on the Si02 substrate under Ar+1%H2 gas exposure, plotted as a function of hydrogen originally contained in the film.

Fig. 5. Biosynthetic pathways for (I) 6-methylsalicylic acid and (II) the triacetic acid lactone. The structures of the intermediates have not been identified. The stereochemical course of the prochiral carbons (C-2 and C-4 in the triketide intermediate, C-3 and C-5 in 6-MSA) was investigated using R)- and (S)- [l- C,2- H]malonic acid extender substrate analogs in a coupled assay with 6-MSAS and succinyl-CoA transferase. The distinguishable hydrogens originating from the chiral malonyl CoA are labeled with H and H. Triacetic acid lactone synthesis is catalyzed by 6-MSAS in the absence NADPH...

These are reactions that incorporate metals into organic rings. The most common of these are orthometallations, oxidative additions in which the ortho position of an aromatic ling becomes attached to the metal. The first example in Figure 14-4 is an OA in which an ortho carbon and the hydrogen originally in the ortho position add to iridium. 

The removal of ions disturbs the equilibrium between the weak acid and its ions. Consequently, more HA ionizes to reestablish the equilibrium. The newly produced ions can then be neutralized by more OH" and so on until all of the hydrogen originally present is neutralized. The overall result, the sum of reactions 1 and 2, is the titration of HA with OH". 

A gaseous binary compound has a vapor density that is 1.94 times that of oxygen at the same temperature and pressure. When 1.39 g of the gas is burned in an excess of oxygen, 1.21 g water is formed, removing all the hydrogen originally present. 

Promotional effects of Co or Ni are also construed in terms of a "remote control" theory proposed by Delmon and co-workers [3]. On the basis of the findings that catalytic synergies are generated even for physical mixtures of supported component sulfides, it is claimed in this theory that the catalytic, activity of Mo sulfides is enhanced by spillover hydrogen originally generated on highly dispersed Co or Ni promoter sulfides in the proximity. 

It has not yet been possible to show that the hydrogen originally at C-24 in cycloartenol is still present in the same position in the final alkylated products... 

The fate of the 3 -H of the substrate after its abstraction by RDPR or RTPR has been studied with [3 - H]UDP (46) and [3 - H]UTP (47), respectively. Examination of the 2 -deoxy products via NMR spectroscopy indicated the presence of deuterium in the 3 -position. Taken together with the tritium isotope effect studies, these results indicate that the hydrogen originally removed from the 3 -position of the substrate is returned to the same position in the products. 

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