Rate constant ranges

Acyl radicals undergo dccarbonylation. For aliphatic acyl radicals the rate constant for decarbonylation appears to be correlated with the stability of the alkyl radical formed. Values of the dccarbonylation rate constant range from 4 s for CH3C 0) to 1.5x10s s l [lor (CH.,)2C(Ph)C( )0] at 298 °C.3M The loss of carbon monoxide from phenacyl radicals is endothermic and the rate constant is extremely low (ca 10 8 s 1 at 298 nC).388 Consequently, the reaction is not observed during polymerization experiments. 

Biological. Following a lag time of 20 to 25 h, acetone degraded in activated sludge (30 mg/L) at a rate constant ranging from 0.016 to 0.020/h (Urano and Kato, 1986). Soil bacteria can... 

In water, carbofuran reacted with OH radicals at a first-order rate constant of 2.2 x 10 /M-sec (Mabury and Crosby, 1996a). Benitez et al. (2002) reported an apparent pseudo-first-order rate constant ranging from 5.1 x 10to 19.5 x lO Vsec for the reaction of carbofuran with ozone in water. When ozone and UV radiation was used to study the degradation kinetics, the pseudo-first-order rate constant was 22.8 x 10 Vsec. Similarly, the oxidation of carbofuran by Fenton s reagent and UV radiation ranged from 17.2 x 10 to >200 x lO Vsec. 

Photolytic. A rate constant 9.70 x lO" cmVmolecule-sec was reported for the reaction of thiophene and OH radicals in the atmosphere at room temperature (Atkinson, 1985). Thiophene also reacts with NO3 radicals in the atmosphere at rate constants ranging from 3.2 x 10 (Atkinson et ah, 1985) to 3.93 x lO" cmVmolecule-sec (Atkinson, 1991). 

The amount of data available for nickel (I I) allows some generalizations, although it must be remembered, that with the variety of experimental techniques and conditions, little reliance should be placed on small differences in separate values. Second-order rate constants range from 2 X 105 (HEDTA3) through 3 X 103 (NH3) to a value as low as 3.5 (Hate4 3), a variation understandable in terms of the proposed mechanism. 

Class IV. The exchange of water is slow. These are the only inert complexes. First-order rate constants range from 10 1 to I0-9 s-1. These ions are comparable in size to Class III ions and exhibit considerable LFSE Cr3+(rf3), Ru3+(k>w spin d5), Pt2+ (low spin d8). Best estimates for Co3+, which oxidizes water and is therefore unstable in aqueous solution, also place it in this class. 

The quenching of H(2P) atoms by small molecules has been studied extensively by Phillips et al. (1021-1023) and by Tanaka et al. (583, 960). The quenching rate constant ranges from 10 8 [Shukla et al. (874)] to 10 12 [Wauchopet al. (1023)] cm3 molec-1 sec-1 both for N2 and 02. The discrepancy is partially due to resonance trapping of the 1216 A line in the optically thick system. In the optically thin system the value is about 10-9 cm3 molec- 1 sec-1 [Braun et al. (142)]. The reaction of H(2P) atoms with H2 appears to produce three ground state H atoms [Van Volkenburgh et al. (992)]. The reactions of H(2P) atoms with 02 and N2 yielded electronically excited OH and NH [Wauchop and Phillips (1022)], respectively. 

Peroxy radicals(R02) react with organic compounds either by H-atom transfer or addition to a double bond. These reactions have rate constants ranging from <0.01 to 300 M 1 s 1 at 25°C (Howard, 1972 Hendry et al., 1974 Neta et al., 1990) and are rarely important under environmental conditions because of the low average concentration of R02 in surface waters (Table 15.5). However, H-atom transfers from phenol OH or aniline NH have large... 

We have confirmed that this state is a powerful reductant by an investigation of the electron transfer quenching of [Ir(p-pz)(COD)]jf by a series of pyridinium acceptors with varying reduction potentials (Figure 2 Table I). For acceptors with reduction potentials of t -1.5 to -1.9 V (vs. SSCE, CH3CN), the quenching rate constants range from 8 x 10 to 1 x 10 M ls l. The important point is... 

Another distance dependence investigation was carried out by Harriman, Ziessel, and coworkers on [(tpy)Ru(BL)Os(tpy)]4+ donor/acceptor complexes having a bridging ligand (BL) with the structure tCC(PhCC)xl (Scheme 4, x = 1-5). While the absolute energy transfer rate constants ranged from 1.1 x 108 s 1 for x = 1 to 2 x 106 s-1 for x = 5, the resulting distance dependence yielded a very small ft value of 0.2 A-1. The authors comment on the... 

Table 4 lists calculated average shear rate constants and SDs of 10.24 0.55 (0.75% guar gum solution) and 10.36 0.27 (1.0% guar gum solution). The SDs are minimal. The average shear rate constant range calculated by Rieth (3) was 10.45-10.91 for the same helical impeller. The calculated overall average shear rate constant of 10.30 falls below the range reported by Rieth (3). 

Rate constants for the reactions of S0o with a wide variety of organic compounds are summarized in Table 2. The sulfite radical was found to oxidize ascorbate, trolox (a water soluble tocopherol derivative), methoxyphenol, hydroquinone and other phenolic compounds, sulfonated hydroquinones, phenylenediamines, and phenothiazines with rate constants ranging to 1 CrM 1 s. ... 

Fleischmann et al s 34 report cyclic voltammetry data for the oxidation of a series of aromatic hydrocarbons in a molten salt electrolyte, AlCl3-NaCl-KCl at 150°. Electrooxidation in this medium occurs at unusually low oxidation potentials. Tris-(p-substituted phenyl)amines, with the exception of tri (p-nitrophenyl) amine, yield very stable radical cations by all electrochemical criteria 380>S42 Mono- and bis-p-substituted triphenylamines, however, dimerize with rate constants ranging from 101 to 10s M 1 sec 1 to benzidines 176 (Eq. (237)), which subsequently are oxidized to the radical cations 177, whose ESR-spectra are observed. Dimerization is fastest with the p-N02 andp-CN-derivative, in accordance with HMO calculations, which predict the highest spin sensity in the p-position of these compounds 542 ... 

It has been common practice to equate the value of )3 with the degree of proton transfer in the transition state /3 values close to 0 are taken to be indicative of reactant-like transition states and those close to 1 of product-like transition states. Any value outside these limits is inconsistent with this practice. Early investigators were only able to follow reactions within a limited rate constant range. With the development of fast reaction techniques (Eigen, 1964 Caldin, 1964) the predicted (Br nsted and Pedersen, 1923) curvature of the plots was fully established (cf. Bell and Lidwell, 1940). Pronounced curvature is in fact seen for fast proton transfers in DMSO (see p. 156). 

The electrochemical techniques do not differ significantly with respect to time resolution. Pseudo first order rate constants ranging from about 0.1 to 10 S can be measured by techniques which monitor the response of the intermediate and LSV and electrocatalysis can give estimates of rate constants as high as 10 s . In the opinion of the author, the factors of most importance to be considered in selecting a measurement method of the first style are (i) the selectivity of the response, (//) the ease of obtaining reliable data, and (ill) the kinetic or thermodynamic information content of the data. Another factor of utmost importance to the non-specialist is (iv) the availability of instrumentation. 

An earlier experimental study involved the generation of benzylchlorocarbene, phenylchlorocarbene, methoxy-phenylcarbene, dimethylcarbene, cyclobutylidene, adamantylidene, and fluorenylidene by means of laser flash photolysis and their reactions with oxiranes and thiiranes <1998JA8681>. Absolute rate constants ranging from 10 to 10 ° M s at 22 °C were measured in acetonitrile and cyclohexane. Thermally generated dimethoxycarbene was found to be inefficient at abstracting oxygen or sulfur from an oxirane or a thiirane. 

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