Rate constants table

The rate of acid-induced demetalation depends only slightly on the nature of the head substituents X (Table I). In contrast, the tail-R groups dramatically affect k and, for the most part, k3, suggesting that tail amide O-atoms are sites of peripheral protonation. Thus, the acid tolerant Fem-TAML catalysts with tail electron-withdrawing groups should be more acid resistant and replacement of R = Me with R = F results in a remarkable stabilization. The rate constants (Table I) show that under weakly acidic conditions (pH 2-3), when the k pathway dominates over k3, fluorinated lk is 105-fold more H +-tolerant than la. 

Tables I, III, V, and VII give the kinetic mass loss rate constants. Tables II, IV, VI, and VIII present the activation parameters. In addition to the activation parameters, the rates were normalized to 300°C by the Arrhenius equation in order to eliminate any temperature effects. Table IX shows the char/residue (Mr), as measured at 550°C under N2.

Lai + COCH3)2 Lai + COCH3)3 and Lai + COCH3)4 computed from the Af1, Af5, k223 and k2A rate constants (Table 4), and their speciation as a function of (pH. Reproduced from ref. 10b with permission. 

Physiological parameters for volumes and blood flow of the compartments are listed in Table 2-4. Physiologic constants (compartment volume, blood flows, etc) were taken from published values. Values for the solubility of n-hexanc in blood and tissues (partition coefficients) are taken from human tissue (Perbellini et al. 1985). Rate constants (Table 2-4, Figure 2-5) were estimated from animal and human data and are all assumed to be first-order. 

The dioxo complexes of W(IV) and Mo(IV), having high pKa values (Table II), are formed via hydrolysis as the rate-determining step (Scheme 4) and the observed rate constants for the inversion along the O-M-O axis for the W(IV) and the Mo(IV) complexes are therefore defined by Eq. (18). These were calculated as a function of pH, using the proton exchange rate constants (Table IV) and the acid dissociation constants (Table II)... 

Other important aromatic amines such as chlorpromazine (26) have also been subjected to oxidation studies using oxidants produced by pulse radiolysis. Typical among these is the use of chloroalkylperoxyl radicals formed by pulse radiolysis in a variety of solvents. These oxidants yield the corresponding radical cation. The rate constants (Table 3) for these reactions were determined42. Other studies have determined the reactivity between chlorpromazine and BiV- in H2O/DMSO in varying proportions. The rate constants for the formation of the radical cation of chlorpromazine were similar in value to those obtained from the peroxy radical reactions4. 

Experimental and predicted volatilization rate constants for the five pesticides are listed in Table II. It should be noted that, despite low H values for the pesticides, experimental volatilization rates for diazlnon and parathlon are fairly rapid from water under the conditions of our tests (t> of 4.2 and 9.6 days, respectively). When compared to their hydrolysis rate constants (Table I), volatilization can be seen to be a more important route of loss than hydrolysis for diazlnon, parathlon, and methyl parathlon. The relative volatilization rates reported here for diazlnon and parathlon are in good agreement with those reported by Lichtenstein (14). 

Studies using smaller implants of 2.9 mm diameter indicated statistically significant differences in the two rate constants (Table 2) and extent of drug released from the implant in comparison with implants of mean diameter 6.2 mm. This could be attributed to an increase in surface area per unit volume of the smaller implant. 

In the amorphous tram- and the side vinyl polybutadienes, the first-order reaction rate constants (Table III) give high initial yields (G0) for olefin disappearance when the initial concentration is inserted in the rate equation kD = n(CJCD), where k = rate constant, C = initial concentration, and CD = concentration after dose D. The activation energies for the disappearance of both these olefinic species range from 3.4 to 4.0 keal. per mole, not very different from the activation energy observed for cis disappearance. 

Although it is not known whether the base is an essential feature of a substrate, the nucleoside moiety is necessary since bis- and tris-p-nitrophenyl phosphate esters are not hydrolyzed (61). The nature of the R substitution on the 3 -OH clearly affects the affinity of the substrate or inhibitor for the enzyme, even though it does not affect the maximal catalytic rate constant (Table I). The importance of the 5 - and 3 -phosphate groups in determining the affinity of inhibitors (3, 66) is consistent with the contribution of these groups to substrate affinity (61). These effects result from the phosphoryl groups themselves rather than... 

The hydrolysis of p-trifluoromethylphenyldimethylethoxysilane was carried out at four different acid concentrations and the rate constants were calculated (Table 8). If the reaction is first order in acid, the rate constant should not change as shown in Table 8. Each of the alkoxysilanes was hydrolyzed with a ten-fold excess of water. If the rate equation is correct, water does not react until after the rate determining step and should not affect the rate constants (Table 9).- Again, this is the case. If the mechanism proceeded through a pentavalent state such as Smith suggested, we would expect to see water involved in the rate equation. At this point, Jada s mechanism seems more likely. 

Initially studies of metal ion-promoted hydrolysis were centred on simple monoamin esters.36,44,43 However, many of the initial investigations led to rather conflicting results. Th reactions are difficult to study due to the low formation constants of the active complexes. Mor recent measurements46 48 have provided rate constants (Table 4) which show only order c magnitude agreement however, it has been possible to establish that hydroxide ion is th predominant nucleophile at pH values of ca. 5. Higher pH values lead to precipitation of meti hydroxides. Evidence for nucleophilic attack by water has also been obtained.46"48... 

Fig. 10 Empirical relationship between the logarithm of the proton transfer rate constants (Table 1) and the corresponding free energies of reaction ArG°. Triangles (y) k /(M 1 s 1). Filled circles ( ) k /(M 1 s-1). Empty circles (O) kjf/s-1.

Kinetic rate constants, EHomo/ and Hammett s constants can be correlated with reaction rate constants. Table 8.6 summarizes the QSAR models for these volatile compounds. 

First order rate constants (Table VII) varied in the order coal >anthracene> ghenanthrene>coal oil in the temperature range of 450 - 500 c under a pressure of... 

Recently, detailed comparative analyses determined the relative reactivity of HNO from Angeli s salt toward a variety of biomolecules and provided estimates of the rate constants [Table I (147, 209)]. As expected the most facile reactions occurred among HNO and metal complexes, such as Mb02 ( 1 x 107 A/-1 s-1) and metMb ( 8 x 105M 1 s 1), and thiols, particularly GSH ( 2 x 106 AT1 s 1). 

Such is not found experimentally. If a retarding effect is to be quantitated it will likely come from a direct measurement of the excited state rate constants. Table II summarizes the key results to date. 

Although there is a certain trend of q t lues decreasing with increasing rate constants (Table 3), this correlation is far from being linear. This can be seen in particular if q values for the same coupling component, e.g. resorcinol in different acid-base equilibrium forms, are compared. The reactivity of the unionized resorcinol molecule is 7.44 and 11.74 powers of ten lower than its monoanion and dianion, respectively. The monoanion has a comparable reactivity to 3-methoxyphenolate ion as expected. 

Appendix B Specific Reaction Rate Constants TABLE 5 CH4/CH3OH/CH2O/CO/H2/O2 Mechanism ... 

Reductive dimerization of the NAD" " analogues 104a-c, in MeCN, and the reoxidation of the dimers have been studied in detail by CV and LSV [300]. This allowed the estimation of the values and the dimerization rate constants (Table 22). Also in aqueous medium, 104a undergoes fast reductive dimerization, and the 4,4 -tetrahydrodimer was isolated as a mixture of two diastereomers [301]. 

Whereas radioactive decay is never a reversible reaction, many first-order chemical reactions are reversible. In this case the characteristic life time is determined by the sum of the forward and reverse reaction rate constants (Table 9.5). The reason for this maybe understood by a simple thought experiment. Consider two reactions that have the same rate constant driving them to the right, but one is irreversible and one is reversible (e.g. k in first-order equation (a) of Table 9.5 and ki in first-order reversible equation (b) of the same table). The characteristic time to steady state tvill be shorter for the reversible reaction because the difference between the initial and final concentrations of the reactant has to be less if the reaction goes both ways. In the irreversible case all reactant will be consumed in the irreversible case the system tvill come to an equilibrium in which the reactant will be of some greater value. The difference in the characteristic life time between the two examples is determined by the magnitude of the reverse reaction rate constant, k. If k were zero the characteristic life times for the reversible and irreversible reactions would be the same. If k = k+ then the characteristic time for the reversible reaction is half that of the irreversible rate. 

The hydrolysis of alkyl and aryl acetoacetates (HS) possesses pH-independent rate constants (Table 1) corresponding to the decomposition of the conjugate base of the ester (CH3CO-CH"-CO2Ar). Comment on the hydrolysis mechanism considering that the value of PLg for the alkaline hydrolysis of aryl acetates is -0.26. 

---