Rate constants of formation

Lewis and Suhr (1959 b) measured the influence of substituents on the rate of formation and the equilibrium of (jE )-benzenediazocyanide. Ritchie and Wright (1971 b) used the stopped-flow technique to determine the rate constants of formation and the equilibria of substituted (Z)-benzenediazocyanides in water, and also later in methanol. 

The reaction of Co2+ with ROOH limits initiation. In the quasistationary regime, the rate constants of formation and decomposition of hydroperoxide given by the following equations ... 

The ethylene bromonium and 1-bromoethyl cations and their neutral and anionic counterparts have been the subject of a tandem mass spectrometric study of dissociation and gas-phase redox reactions. IR and Raman studies of the bioactive bromonium cation (19), as its hydrogensulfate salt, agree with the results of an X-ray structure determination, and theoretical calculations are also in agreement, except for the details of the NO2 groups. The azaallenium ion (22) is an intermediate in the photolysis of (20) (21) and (22) could both be seen. Flash photolysis of (23) leads to (24), (25), and (26), all of which could be trapped by nucleophiles (27) was not an intermediate. NMR lineshape analysis of the spectmm of (28) leads to reaction rate constants of formation for both the intimate ion pair (29) and the solvent-separated ion pair (30). ... 

Fig. 16 The temperature dependencies of the rate constant of decay of singlet 2-fluorophenyInitrene 15a (1) and the apparent rate constant of formation of triplet 2-fluorophenylnitrene (20a) and ketenimine (18a) (2). Solid lines (1) and (2) results of non-linear global fit of the data to analytical solutions. Insert transient absorption spectra produced by LFP at 295 K (1) of 2-fluorophenyl azide 15a in pentane, detected 500 ns after the laser pulse (2) 4-fluorophenyl azide 15b detected 50 ns after the laser pulse and (3) persistent spectrum detected after 20 s of photolysis of 2-fluorophenyl azide 15a in methylcyclohexane at 77 K.

Rate Constants of Formation and of Propagation of T)x in Toluene at Room Temperature, with Li+ + [211] as Counterion... 

Vinyl fluoride is an interesting monomer, precursor of PVF or Tedlar (produced by the Dupont Company), known for its good resistance to UV radiation. But in telomerisation, the most intensive work was achieved by Tedder and Walton who used several telogens exhibiting cleavable C-Br or C-I bonds, under UV at various temperatures (Table 17). Their surveys were mostly devoted to the obtaining of monoadduct and to their kinetics (e.g., determination of relative rate constants of formation of normal and reverse isomers and of Arrhenius parameters). 

Nagle et al. have reviewed the kinetic scheme that underlies excimer formation, as it applies to Pt complexes [19]. A plot of Id/Im (integrated emission intensities of excimer and monomer bands, respectively) versus concentration of the complex should be linear. The slope is determined by all the rate constants of formation and decay of both excimer and monomer, but is approximately related to the equilibrium constant for excimer formation. Typically for Pt complexes that do show excimer emission, the rate constants for formation and subsequent decay of the excimer are substantially larger than monomer decay. The decay of both monomer and excimer are thus governed by the rate of excimer formation, leading to nearly identical decay kinetics for the two species. 

The a-proton of the external aldimine is then abstracted by a basic residue Bi and the quinonoid intermediate is formed (Fig. 9.13, III). The rate constants of formation of the quinonoid intermediate from L-tryptophan and S-benzyl-L-cysteine are estimated be 940 and 47.6 sec-1, respectively this demonstrates a drastic effect of the leaving group on labilization of the a-proton.78 ... 

It is supposed that any unit of the chain may form a contact with any unit of another chain. Variations of parameters allow the kinetics of dissociation and association in the system to be controlled. Rate constants of formation and disappearance of one contact were estimated122. It is seen on the computer display screen that a strongly defect structures are formed first. In time, these structures go over to completely stretched ones. A completely stretched ladder form of the complex was found to be the most advantageous from the energetic point of view. 

The value for the rate constant of formation of Equation (19) (k ) was obtained to be 90 M s . The key processes for the catalytic extraction of Ni(II)-pan with PADA are the fast aqueous phase formation of NKpada) " " and the adsorption of Ni(pan)(pada)+, followed by the ligand substitution of pada with pan [50]. This scheme is generally of importance as a guideline for the acceleration of the extraction rate using the interfacial reaction. 

There are no data available on the rate of formation of dialkyloxonium ions like protonated 1,3-dioxolane in Eq. (16). It is remarkable that the rate constants of formation of secondary onium ions from linear ethers, acetals, sulfides etc. are also utdcnovra. These should however be lower than the rate constants of proton transfer in water (an upper limit) being close to 10 mole 1 s but certainly higher than the rate constantsof protonation of olefins... 

ZnA+ (HA = amino acid) rapidly associates with the free base porphyrin to form a molecular complex (I) in which ZnA" " is weakly bound to the porphyrin plane. Then the water molecule coordina zincfll) in I dissociates, and zinc(ll) is incorporated into the porphyrin core. Thus the over-all rate constant of formation of zinc(ll) porphyrin in the presence of an amino acid is given by... 

The rate constant for electron transfer is defined as the rate constant of formation of the exciplex state. 

In this equation, Effis the drug effect, iJmax is the maximum effect of drug, ECso is the concentration of drug required to attain half-maximal effect, Cp is the concentration of drug. Precursor is the predecessor for the biomarker, Kq is the rate constant of formation of the precursor. Biomarker is the PD biomarker being described, K ya is the synthesis rate constant of that biomarker, is the degradation rate constant... 

The transient absorption spectra similar to that of the ion-pair state of indole cation radical and flavin anion radical were also observed in D-amino acid oxidase (5), although the spectra were not so clear as those of flavodoxin. In D-amino acid oxidase, the coenzyme, flavin adenine dinucleotide (FAD), is wealtly fluorescent. The fluorescence lifetime was reported to be 40 ps (16), which became drastically shorter (less than 5 ps) when benzoate, a competitive inhibitor, was combined with the enzyme at FAD binding site (17). The dissociation constant of FAD was also marlcedly decreased by the binding of benzoate (17). These results suggest that interaction between isoalloxazine and the quencher became stronger as the inhibitor combined with the enzyme. Absorbance of the transient spectra of D-amino acid oxidase-benzoate complex was remarkably decreased. In this case both rate constants of formation and decay of the CT state could become much faster than those in the case of D-amino acid oxidase free from benzoate. 

Hence, the ratios of rate constants of formation of cyclohexene and 4-methylcyclohexene to that of 4-vinylcyclohexene are calculated by the following equations. 

Transient bivalent gold ions and two unidentified species, possibly Au°, were prepared and stiuded in different aqueous matrices by pulse radiolysis. Their absorption spectra and rate constants of formation and decay are reported. Bivalent gold was prepared by the oxidation of Au(CN)2 in neutral chloride solutions of N20, and also by the reduction of AuClf in the presence of CH3OH. The kinetics of its decay indicates disproportionation. The reduced species of Au(CN)2 from H atoms is different from that obtained with e aq, the latter being attributed to an electron adduct. Both of these species decay, forming colloidal gold. 

Three-component formation was observed for pyrene- and naphtha-lene-/9-CD complexes in the presence of surfactants such as n-alkyl sulfates (chain length C4-C12), n-alkylammonium chlorides (Cj-Cg), and n-al-kyltrimethylammonium bromides (CiQ-Cig) [118]. The two complexes exhibit different behavior in the presence of surfactants. With respect to the value of the two-component system, increased association constants were found for pyrene (short-chain surfactants gave higher constants than long-chain). Lower association constants were found for / -CD-naph-thalene in the presence of surfactants. By following the time course of T-T absorption of the two aromatics in the presence of nitrite, it was found that their different behaviors were due to surfactant influence on the rate constants of formation (k+) and dissociation (k ) of the inclusion compound. For naphthalene, a reduction of k+ was observed in the presence of surfactants while k was unaffected. For pyrene, short-alkyl-... 

Additional work soon discredited this postulate. The 386 nm transient could not be detected in other solvents. No transient was detected upon LFP of 10 in benzene or hexafluorobenzene. In cyclohexane, a transient with X = 367 nm was formed 144 ns after the laser pulse. Only in nitrile solvents were transient absorption bands observed near 400 nm. The definitive experiment was performed by Linda Fladel who demonstrated that the pseudo-first order rate constant of formation of the 386 nm absorbing transient was linearly dependent on the concentration of acetonitrile. This proved that the transient is formed by reaction of an invisible species which reacts with acetonitrile. The observable transient was ylide 12 formed by capture of 11. The same transient was formed by LFP of azirine 13. 

Thus the observed rate constant of formation of probe product AP depends on both and k [P],... 

The reaction of borane with keten forms a single addition product BC2H5O (bimolecular rate constant of formation =4 x 10 1 mol s at low partial pressures of reactants). Kinetic and mass-spectrometric data are consistent with the formulation (64). 

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