Kinetics, acceptor

For the pseudo-homogeneous model St denotes an effective heat of reaction term. The source term for the pseudo-homogeneous model consists of two effective heat of reaction terms, one for the reforming reactions and one for the C02-acceptor kinetics ... 

Acceptor Kinetics. The kinetics of calcining and recarbonation of fresh Virginia dolomite at several spot conditions are shown in Figures 11 and 12. The total pressure was 1 atm. in all cases. 

Equation 17 is valid as long as the incipient fluidizing velocity of the falling particle exceeds the bed fluidizing velocity by about 50%. Obviously adequate control over acceptor residence time consistent with the requirements of acceptor kinetics can be effected in a commercial gasifier by appropriately sizing the acceptor particles. 

The common overall reaction in carbene chemistry is methylene transfer. A (substituted) methylene fragment is eliminated from the "carbene precursor and inserted into the carbene acceptor . Kinetic methods have been widely employed to determine whether divalent carbon intermediates are involved in these reactions. Two major lines of investigation may be distinguished, (/) kinetic studies of the decomposition of carbene precursors, and ( ) determination of the relative rates of product formation. The mechanistic possibilities range from the intervention of free carbenes to fully concerted methylene transfer reactions. 

Keywords Aromatic amines acceptors Kinetics Toxicity... 

Much of chemistry occurs in the condensed phase solution phase ET reactions have been a major focus for theory and experiment for the last 50 years. Experiments, and quantitative theories, have probed how reaction-free energy, solvent polarity, donor-acceptor distance, bridging stmctures, solvent relaxation, and vibronic coupling influence ET kinetics. Important connections have also been drawn between optical charge transfer transitions and thennal ET. 

Actually, collisions in which tlie batli becomes vibrationally excited are relatively rare, occurring witli a typical probability of 1% per gas-kinetic collision [6, 8, H and 13]. More common are processes tliat produce rotational and translational excitation in tlie batli acceptor while leaving tlie molecule in its ground (vibrationless) OO O state. 

The carrier concentrations in doped or extrinsic semiconductors to which donor or acceptor atoms have been added can be deterrnined by considering the chemical kinetics or mass action of reactions between electrons and donor ions or between holes and acceptor ions. The condition for electrical neutraHty is given by equation 6. When the predominant dopants are donors, the semiconductor is... 

Kinetic studies of the reaction of alcohols with acyl chlorides in polar solvents in the absence of basic catalysts generally reveal terms both first-order and second-order in alcohol. Transition states in which the second alcohol molecule acts as a proton acceptor have been proposed ... 

If the enzyme-catalyzed reaction is to be faster than the uncatalyzed case, the acceptor group on the enzyme must be a better attacking group than Y and a better leaving group than X. Note that most enzymes that carry out covalent catalysis have ping-pong kinetic mechanisms. 

In order to distinguish between kinetic and thermodynamic phenomena it is convenient to refer to the former as the 7tr/ i-effect and the latter as the tra/u-influence or static /ra/u-effect". though this nomenclature is by no means universally accepted. However, it appears that to account satisfactorily for the kinetic /rau.s-effect , both it (kinetic) and a (thermodynamic) effects must be invoked to greater or les.ser extents. Thus, for ligands which are low in the Trans series (e.g. halides), the order can be explained on the basis of a u effect whereas for ligands which arc high in the series the order is best interpreted on the basis of a jt effect. Even so, the relatively high position of H , which can have no rr-acceptor properties, seems to be a result of a a mechanism or some other interaction. 

The situation is different, however, in near-neutral or alkaline solutions in which the concentration of HjO will be small (< 10 mol dm ), and in these solutions the water molecule will act as the electron acceptor, and although diffusion occurs rapidly its reduction is kinetically more difficult than that of HjO, and will therefore require a higher activation overpotential. 

However, these observations are not proof of the role of a donor-acceptor complex in the copolymcrization mechanism. Even with the availability of sequence information it is often not possible to discriminate between the complex model, the penultimate model (Section 7.3.1.2) and other, higher order, models.28 A further problem in analyzing the kinetics of these copolyincrizations is that many donor-acceptor systems also give spontaneous initiation (Section 3.3.6.3). 

A true intramolecular proton transfer in the second step of an azo coupling reaction was found by Snyckers and Zollinger (1970a, 1970b) in the reaction of the 8-(2 -pyridyl)-2-naphthoxide ion (with the transition state 12.151). This compound shows neither a kinetic deuterium isotope effect nor general base catalysis, in contrast to the sterically similar 8-phenyl-2-naphthoxide ion. Obviously the heterocyclic nitrogen atom is the proton acceptor. 

Bagal et al. (1975) investigated in more detail the role of donor-acceptor complexes in the azo coupling reaction of the 4-nitrobenzenediazonium ion with 2-naphthylamine-3,6-disulfonic acid and that of the 4-chlorobenzenediazonium ion with 2-naphthol-6-sulfonic acid. Their kinetic results are, as would be expected, compatible with the mechanisms shown in Schemes 12-74 or 12-75. 

Recently, more detailed parameters for hydrogen bonding bases have been introduced and applied to many reactions demonstrating the existence of a linear free energy relationship between the hydrogen bonding donor and acceptor abilities and many kinetic or thermodynamic parameters91. 

The parameter aH is positive for electropositive (electron donor) adsorbates and negative for electronegative (electron acceptor) adsorbates. Even when deviations from linearity exist, the main feature of Eq. (2.23) remain valid and form the basis for understanding the main kinetic features of classical and electrochemical promotion ... 

The spillover effect can be described as the mobility of sorbed species from one phase on which they easily adsorb (donor) to another phase where they do not directly adsorb (acceptor). In this way a seemingly inert material can acquire catalytic activity. In some cases, the acceptor can remain active even after separation from the donor. Also, quite often, as shown by Delmon and coworkers,65 67 simple mechanical mixing of the donor and acceptor phases is sufficient for spillover to occur and influence catalytic kinetics leading to a Remote Control mechanism, a term first introduced by Delmon.65 Spillover may lead, not only to an improvement of catalytic activity and selectivity but also to an increase in lifetime and regenerability of catalysts. 

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