Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Deuterium, dissociation

Of the remaining studies of the overall reaction between deuterium and oxygen, the measurements of the first explosion limit by Kurzius and Boudart [58], and their deduction of an expression for in the temperature range 800—1000 K, have already been discussed in Sect. 3.6.4. A shock tube study of the development of the ignition, as well as of deuterium dissociation in the presence of argon and the isotopic exchange reactions (xxiv) and (xxv)... [Pg.147]

Samson P, Nesbitt A, Koel BE, Hodgson A (1998) Deuterium dissociation on ordered Sn/ Pt(lll) surface alloys. J Chem Phys 109 3255... [Pg.50]

In benzene solution one of the triphenylphosphine ligands in (131) is replaced by a solvent molecule to give intermediate (132). The latter can add a mole of deuterium leading to (133) or can equilibrate with (134) in the presence of an olefin. There is some evidence, however, that in the presence of alcohol and oxygen the dissociation step (131 -> 132) is inhibited and the displacement of the triphenylphosphine by the solvent in forming (133) occurs only in the presence of hydrogen (or deuterium). ... [Pg.184]

Hydrogen was recognized as the essential element in acids by H. Davy after his work on the hydrohalic acids, and theories of acids and bases have played an important role ever since. The electrolytic dissociation theory of S. A. Arrhenius and W. Ostwald in the 1880s, the introduction of the pH scale for hydrogen-ion concentrations by S. P. L. Sprensen in 1909, the theory of acid-base titrations and indicators, and J. N. Brdnsted s fruitful concept of acids and conjugate bases as proton donors and acceptors (1923) are other land marks (see p. 48). The di.scovery of ortho- and para-hydrogen in 1924, closely followed by the discovery of heavy hydrogen (deuterium) and... [Pg.32]

Much evidence has been obtained in support of the El mechanism. For example, El reactions show first-order kinetics, consistent with a rate-limiting spontaneous dissociation process, l- urthermore, El reactions show- no deuterium isotope effect because rupture of the C—H (or C—D) bond occurs after the rate-limiting step rather than during it. Thus, we can t measure a rate difference between a deuterated and nondeuterated substrate. [Pg.392]

In the El reaction, C-X bond-breaking occurs first. The substrate dissociates to yield a carbocation in the slow rate-limiting step before losing H+ from an adjacent carbon in a second step. The reaction shows first-order kinetics and no deuterium isotope effect and occurs when a tertiary substrate reacts in polar, nonbasic solution. [Pg.397]

A dissociative mechanism is indicated by the fact that excess phosphine inhibits elimination from molecules like m-Pd(PPh3)2Me2 and Pt(PPh3)2Bu2. On thermolysis of mixtures where one molecule contains deuterium, such as... [Pg.220]

More recently, a number of reports dealing with 1,3-sulfonyl shifts which proceed by other mechanisms have been published. For example, Baechler and coworkers suggested that the higher activation enthalpy observed for the isomerization of the deuterium labeled methallyl sulfone 72 in nitrobenzene at 150°C as compared to the corresponding sulfide, together with the positive entropy of activation may be taken as evidence for a homolytic dissociation mechanism (equation 44). A similar mechanism has also been suggested by Little and coworkers for the gas-phase thermal rearrangement of deuterium labelled allyl sec-butyl sulfone, which precedes its pyrolysis to alkene and sulfur dioxide. [Pg.688]

Selective removal of the iodine from fluorinated compounds was performed by 5% Pd/C catalyzed hydrogenolysis in the presence of triethylamine or sodium acetate.467 Ra-Ni and 1% NaOH were used for the cleavage of the C-I bond.468 The adsorption of chloroiodomethane was studied on a Pt(lll) surface. Dissociation began with C—I bond cleavage at about 150 K. Co-adsorbed deuterium atoms weaken the bonding between the starting compound and the surface and decrease the amount of dissociated molecules.469... [Pg.190]

Deuterium exchange within saturated products occurs by dissociative adsorption followed by multiple stepwise migrations as described in assumption 15 followed by the addition of deuterium and/or hydrogen from the equilibrated surface hydrogen-deuterium pool. [Pg.293]

We shall assume that the molecules H2 and D2 dissociate into ions upon adsorption. Let us also assume that the adsorption centers for deuterium atoms are the same as for hydrogen atoms. The question as to the nature of these centers is here of no interest. We shall denote the surface concentration of adsorption centers by N. The surface concentrations of the chemisorbed atoms of hydrogen and deuterium are denoted, respectively, by JVh and Nd. Let us further assume that the surface is saturated by hydrogen and deuterium atoms so that... [Pg.182]

The spectra of C3H6 and C3D6 show that chemisorption of propylene is dissociative, but they fail to identify which carbon-hydrogen bond is broken on adsorption. To this end the spectra of a number of deuterium-labeled propylenes were studied and compared. These results are summarized in abbreviated form in Table VI, which specifies the hydrogen fragment formed on adsorption the fragment was identified as an OH if a band appeared near 3593 cm-1 or as an OD if a band appeared near 2653 cm-1. In those cases where the spectrum changed with time the summary... [Pg.32]


See other pages where Deuterium, dissociation is mentioned: [Pg.207]    [Pg.207]    [Pg.318]    [Pg.299]    [Pg.106]    [Pg.89]    [Pg.688]    [Pg.297]    [Pg.55]    [Pg.271]    [Pg.97]    [Pg.105]    [Pg.221]    [Pg.208]    [Pg.499]    [Pg.30]    [Pg.24]    [Pg.32]    [Pg.41]    [Pg.45]    [Pg.103]    [Pg.60]    [Pg.133]    [Pg.134]    [Pg.135]    [Pg.135]    [Pg.136]    [Pg.138]    [Pg.140]    [Pg.142]    [Pg.143]    [Pg.12]    [Pg.41]    [Pg.129]    [Pg.373]    [Pg.471]    [Pg.476]    [Pg.821]   
See also in sourсe #XX -- [ Pg.10 , Pg.19 ]




SEARCH



© 2024 chempedia.info