Pseudo-unimolecular rate constants

Pseudo-unimolecular rate constants measured at various temperatures, one of which is tabulated. 

Pseudo-unimolecular rate constant in sec. f Water was added to absolute ethanol to make 99.8% ethanol. 

Plots of the concentration of carboxylate formed vs. time were drawn for each copolymer, and the initial rates of hydrolysis were determined by measurement of the slope of the tangent to the curve at zero time. The pseudo-unimolecular rate constant (K) is given by ... 

The calculated pseudo-unimolecular rate constants (k) for the hydrolysis reaction [Fig. 3], clearly show the inhibiting effect of AMPS, relative to sodium acrylate at all three temperatures. 

The first indication that A-acyloxy-A-alkoxyamidcs reacted by an acid-catalysed process came from preliminary H NMR investigations in a homogeneous D20/ CD3CN mixture, which indicated that A-acetoxy-A-butoxybenzamide 25c reacted slowly in aqueous acetonitrile by an autocatalytic process according to Scheme 4 (.k is the unimolecular or pseudo unimolecular rate constant, K the dissociation constant of acetic acid and K the pre-equilibrium constant for protonation of 25c).38... 

Upon addition of a solution of sulfuric acid in D20 the reaction of A-acetoxy-A-alkoxyamides obeys pseudo-unimolecular kinetics consistent with a rapid reversible protonation of the substrate followed by a slow decomposition to acetic acid and products according to Scheme 5. Here k is the unimolecular or pseudo unimolecular rate constant and K the pre-equilibrium constant for protonation of 25c. Since under these conditions water (D20) was in a relatively small excess compared with dilute aqueous solutions, the rate expression could be represented by the following equation ... 

Pseudo unimolecular rate constants k for sulfuric acid-catalysed solvolysis of 25c in CD3CN/D20 (adjusted to a constant ratio of 3.8 1) were found to be linearly dependent upon the acid concentration (Fig. 11) and the gradient afforded a composite rate constant of (2.41+0.10) x 10 2lmol 1 s-1 at 308K. From the intercept, ka, the rate constant for uncatalysed solvolysis, was at least three orders smaller and zero within experimental error. A similar linear dependence and near-zero uncatalysed rate constant was demonstrated for other /V-acetoxy-TV-alkoxybenzamides given in Table 3. 

The lifetime of the excited state (i°) is equal to the reciprocal of the sum of the (pseudo)unimolecular rate constants of all processes that cause the decay ... 

Lifetime (t) The lifetime of a molecular entity which decays in a first-order process is the time needed for a concentration of the entity to decrease to 1/e of its original value. Statistically, it represents the life expectation of the entity. It is equal to the reciprocal of the sum of the (pseudo)unimolecular rate constants of all processes which cause the decay. Lifetime is used sometimes for processes which are not first order. However, in such cases, the lifetime depends on the initial concentration of the entity, or of a quencher and therefore only an initial or a mean lifetime can be defined. In this case it should be called apparent lifetime, instead. Occasionally, the term half-life (T1/2) is used, representing the time needed for the concentration of an entity to decrease to one half of its original val-... 

At atmospheric pressure and in the presence of an unchanging concentration of positive ions P, the bimolecular rate constants can be replaced by pseudo-unimolecular rate constants k[> = k D[P] and 1approximately temperature-independent because recombination is exothermic since the energy is... 

For Eq. (3.10) and Eq. (3.12) the bimolecular rate constants can be replaced with pseudo unimolecular rate constants within the limits of either fractional electron capture or constant positive ion concentration. All the above reactions take place on a time scale that is fast relative to the time required for transport through the detector. Under steady state conditions the electron capture coefficient K (see Eq. 3.7) is given by... 

Let us now analyse the information that can be extracted from steady-state fluorescence data. First we note that the matrix of rate constants k (Eq. 15.57) contains two pseudo-unimolecular rate constants, k.iEH" ] and (Eq. 15.58,... 

Pseudo-unimolecular rate constant (h ) at 91-6 t 90 0°. % For data on a number of primary aromatic amines see (cf. Table 5.19). Reaction too slow to permit calculation of accurate Arrhenius parameters. 

Bq(s) = magnetic field experienced by sample k, k, m = rate constants for activation, deactivation, reaction kuj,i = macroscopic pseudo-unimolecular rate constant a = shape factor = (sample) volume susceptibility qNMR = rotationally inelastic cross section. 

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