Hydride molecules with

Such simple considerations led Scholten and Konvalinka to confirm the form of the dependence of the reaction velocity on the pressure, as had been observed in their experiments. Taking into account a more realistic situation, on the polycrystalline hydride surface with which a hydrogen molecule is dealing when colliding and subsequently being dissociatively adsorbed, we should assume rather a different probability of an encounter with a hydride center of a /3-phase lattice, an empty octahedral hole, or a free palladium atom—for every kind of crystallite orientation on the surface, even when it is represented, for the sake of simplicity, by only the three low index planes. 

A low ion pair yield of products resulting from hydride transfer reactions is also noted when the additive molecules are unsaturated. Table I indicates, however, that hydride transfer reactions between alkyl ions and olefins do occur to some extent. The reduced yield can be accounted for by the occurrence of two additional reactions between alkyl ions and unsaturated hydrocarbon molecules—namely, proton transfer and condensation reactions, both of which will be discussed later. The total reaction rate of an ion with an olefin is much higher than reaction with a saturated molecule of comparable size. For example, the propyl ion reacts with cyclopentene and cyclohexene at rates which are, respectively, 3.05 and 3.07 times greater than the rate of hydride transfer with cyclobutane. This observation can probably be accounted for by a higher collision cross-section and /or a transmission coefficient for reaction which is close to unity. 

This is the first example of a proton transfer process to a hydride complex with a second-order dependence. Theoretical calculations indicate that the role of the HX molecules is the formation of W-H H-Cl- H-Cl adducts that convert into W-Cl, H2 and HCl2 in the rate-determining state through hydrogen complexes as transition states. 

The resulting complex wonld be a hydride species with two further solvent molecules. Further studies are required to identify the stracture of this species (11). 

An unusual cationic domino transformation has been observed by Nicolaou and coworkers during their studies on the total synthesis of the natural product azadirachtin (1-105) [30]. Thus, exposure of the substrate 1-106 to sulfuric acid in CHjClj at 0°C led to the smooth production of diketone 1-109 in 80% yield (Scheme 1.27). The reaction is initiated by proto nation of the olefinic bond in 1-106, affording the tertiary carbocation 1-107, which undergoes a 1,5-hydride shift with concomitant disconnection of the oxygen bridge between the two domains of the molecule. Subsequent hydrolysis of the formed oxenium ion 1-108 yielded the diketone 1-109. 

Methylzinc hydride was formed by the insertion of excited zinc atoms, in their 3Pi state, into the C-H bond of methane in an argon matrix.229 The MeZnH product was characterized on the basis of its infrared spectrum and determined to be a linear molecule with C v symmetry. The band at 1866.1 cm-1 is due the Zn-H stretch, while the band at 565.5 cm-1 was assigned to the Zn-C stretching vibration. Additional bands for isotopically labeled species were also reported. 

The reaction of [Ni(ethene)3] with a hydride donor such as trialkyl(hydrido)-aluminate results in the formation of the dinuclear anionic complex [ Ni(eth-ene)2[2l 11 [22]. The nickel(O) centers in this complex are in a trigonal planar environment of two ethene molecules and a bridging hydride ion, with the ethene carbons in the plane of coordination. The two planes of coordination within the dinuclear complex are almost perpendicular to each other, and the Ni-H-Ni unit is significantly bent, with an angle of 125° and a Ni-Ni distance of 2.6 A [22],... 

Several reaction pathways for the cracking reaction are discussed in the literature. The commonly accepted mechanisms involve carbocations as intermediates. Reactions probably occur in catalytic cracking are visualized in Figure 4.14 [17,18], In a first step, carbocations are formed by interaction with acid sites in the zeolite. Carbenium ions may form by interaction of a paraffin molecule with a Lewis acid site abstracting a hydride ion from the alkane molecule (1), while carbo-nium ions form by direct protonation of paraffin molecules on Bronsted acid sites (2). A carbonium ion then either may eliminate a H2 molecule (3) or it cracks, releases a short-chain alkane and remains as a carbenium ion (4). The carbenium ion then gets either deprotonated and released as an olefin (5,9) or it isomerizes via a hydride (6) or methyl shift (7) to form more stable isomers. A hydride transfer from a second alkane molecule may then result in a branched alkane chain (8). The... 

The 222 enthalpies of formation included in the G3/99 test set contain a wide variety of molecules with many different kinds of bonds. They are conveniently classified into subgroups of molecules. They include 47 molecules containing non-hydrogen atoms, 38 hydrocarbons, 91 substituted hydrocarbons, 15 inorganic hydrides, and 31 open-shell radicals. Together, they provide a comprehensive assessment of new theoretical models in a wide variety of bonding environments. 

CHC13 CeHs (CH3)2C0 CH4 metal hydrides, or protons in molecules with shift reagents added... 

Palladium hydride is not a stoichiometric chemical compound but simply a metal in which hydrogen is dissolved and stored in solid state, in space between Pd atoms of crystal lattice of the host metal. Relatively high solubility and mobility of H in the FCC (face-centered-cubic) Pd lattice made the Pd H system one of the most transparent, and hence most studied from microstructural, thermodynamic, and kinetic points of view. Over the century that followed many metal-hydrogen systems were investigated while those studies were driven mostly by scientific curiosity. Researchers were interested in the interaction of hydrogen molecule with metal surfaces adsorption and diffusion into metals. Many reports on absorption of in Ni, Fe, Ni, Co, Cu, Pd, Pt, Rh, Pd-Pt, Pd-Rh, Mo-Fe, Ag-Cu, Au-Cu, Cu-Ni, Cu-Pt, Cu-Sn, and lack of absorption in Ag, Au, Cd, Pb, Sn, Zn came from Sieverts et al. [30-33]. 

Fig. 8). Signals from molecules with ratios of anhydride (A)/diisopropanol-amine (D) of n n and n (n-b 1) were predominantly observed. Other signals, for example composed of n (n+2), n (n+3), etc., indicative of the reaction proceeding via pathway C in Fig. 6 (observed abundantly in resins made of diethanolamine) appeared only in minor amounts. The signals with n n ratios of an-hydride/diisopropanolamine, also present in minor amounts (usually between 5% and 20%) compared to the n (n-i-1), can be ascribed to cycle formation [14]. The relative abundance of these perspective peak series varied considerably with the monomer ratios, i. e., molecular weights and the type of cyclic anhy-... 

The reaction of atoms, radicals or excited triplet states of some molecules with silicon hydrides is the most important way for generating silyl radicals [1,2]. Indeed, Reaction (1.1) in solution has been used for different applications. Usually radicals X are centred at carbon, nitrogen, oxygen, or sulfur atoms... 

Pines and Kolobielski (18) have shown that phenylcyclohexene, although it is not a cyclic diolefin, will also undergo reactions similar to those that cyclic diolefins undergo when treated with base catalysts. When heated to 200-220 with a sodium-benzyl-sodium catalyst, it underwent a hydrogen transfer reaction resulting in the formation of biphenyl and of phenyl-cyclohexane molecular hydrogen was not produced. The mechanism of this reaction may be pictured as an elimination of sodium hydride from one molecule with the hydride ion being accepted by another molecule (A"-E"). 

Catalysis of hydrosilylation by dimeric or by monomeric rhodium (and iridium) siloxide complexes occurs via preliminary oxidative addition of siUcon hydride followed by elimination of disiloxane (detected by GC/MS) to generate the square planar 16e hydride complex with an already coordinated molecule of alkene (Scheme 7.7). 

Scheme 10.8 represents proton transfer to hydride ligands with the participation of two proton donor molecules, emphasizing the role of homoconjugated [X- H X] species in the kinetics of the process. Note that the second HX molecule initiates the formation of the solvent-separated or contact ion pair, corresponding to pathway (1) or (2). Following the principles of formal kinetics, pathway (1) can be expressed via... 

A -bromo derivative (37.1.1.45), which is reacted with sodium ethoxide realizing the key moment of the synthesis—the transformation of the piperidine derivative to a quinuclidine derivative (37.1.1.46). Reducing the keto group in this molecule with lithium aluminum hydride gives the desired quinine (37.1.1.47) [17-22]. 

Both P-hydride transfers result in polypropene molecules with one vinylidene and one n-propyl end group. The two transfers are zero- and first-order, respectively, in monomer. P-Hydride transfer yields vinyl end groups in ethylene polymerization. 

An alternative way of envisaging hydride formation is by reaction of a neutral molecule with H, hydride ion. The -ate termination is again used. 

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