Relative Arrhenius parameters

In a senes of papers. Tedder and co-workers reported the factors determining the reactivity of perfluormated radicals with various fluoroethylenes Relative Arrhenius parameters for tnfluoromethyl radicals [17] and pentafluoroethyl radicals [/5] were determined, with higher selectivity demonstrated for the higher homologue Selectivity of addition to unsymmetncal olefins was found also to increase with greater radical branching [19]... 

Table 7 in Section 3, showed that the pre-exponential, 4-factor for the addition of alkyl radicals to olefins is of the order 10s 1 mol-1 s-1. Table 17 (p. 68) lists the relative Arrhenius parameters (taking ethylene as standard) for the addition of a wide range of halogenoalkyl radicals to fluoroethylenes. These tables correspond to the relative rate tables discussed in Section 5 in which the... 

Relative Arrhenius parameters (ethylene as standard for the addition of alkyl radicals to propene and fluoropropenes... 

The kinetics of the reactions of alkoxy radicals have been reviewed and evaluated by Gray et al. [369]. Results for H-abstraction reactions of methoxy radicals are shown in Table 33. It is not possible with alkoxy radicals to monitor the radical concentrations by measuring the rates of formation of the dimers since these are peroxides which are difficult to analyse. The reactions of methoxy radicals with alkanes were studied indirectly by measuring the rates of consumption of the alkanes in competitive experiments involving pairs of reactants [366]. This yielded relative Arrhenius parameters which were put on an absolute basis by... 

Metathetical reactions of trichlorosilyl radicals. Relative Arrhenius parameters for the reactions SiCl3 + RX XSiCl3 + R... 

Tables 111 and IV show the relative Arrhenius parameters for the addition of a wide variety of radicals to fluoroethylene,...

Table V shows the relative rates for addition at 150° and most of the data comes from Tables III and IV. However two radicals (CH2C1 and CBr3. ) are included in this Table for which no accurate temperature variation is available. The general pattern of results confirms the picture built up from the tables of relative Arrhenius Parameters. The relative rates are the results of direct measurement and therefore probably represent a more accurate summary. A very noticeable feature of Table V is the low rates of addition of heptafluoro-iso-propyl radicals to CHF- and CF2- sites. This strongly suggests that classical "steric hindrance" plays a significant role in free radical addition.

It should be noticed that the products M2 are derived from the solute and therefore are not formed by molecular processes. Consequently the experimentally determined values of G(M2) can be substituted directly into expression VII. Since [KH] and a are known, this expression can then be used to obtain the rate constant ratio kj /k and the respective relative Arrhenius parameters E -0.5Et and This method was used in the deri-... 

Another situation exists in BrCH2CN and CCI3CN solutions, where at very low solute concentrations, GCCH3CN) and G(CHCl2CN) reach constant values. Since the alkane concentration is constant this can happen only if IM] [R]. Under these conditions expression VIII can be used for the derivation of kii/k. . The relative Arrhenius parameters of the H transfer reactions of... 

Table III. Relative Arrhenius Parameters of H Atom Transfer...

In trichlorosilane the chain decomposition of chloromethanes, CM, proceeds by reactions 52 and 53. In the ClsSiH-ClM systems the relative Arrhenius parameters of the Cl atom transfer, reaction 52, were determined in competitive studies (41). The same method was... 

Kinetic data are available for the range 7S S 98 i % sulphuric acid, and Arrhenius parameters at several acidities. The relative rate was obtained as before. 

Viswanadhan and Matticc278 carried out calculations aimed at rationalizing the relative frequency of backbiting in these and other polymerizations in terms of the ease of adopting the required conformation for intramolecular abstraction (see 2.4.4), More recent theoretical studies generally support these conclusions and provide more quantitative estimates of the Arrhenius parameters for the... 

RELATIVE RATES AND ARRHENIUS PARAMETERS FOR REACTION OF XC6H4NMe+ AND... 

In Section 3.4, traditional methods of obtaining values of rate parameters from experimental data are described. These mostly involve identification of linear forms of the rate expressions (combinations of material balances and rate laws). Such methods are often useful for relatively easy identification of reaction order and Arrhenius parameters, but may not provide the best parameter estimates. In this section, we note methods that do not require linearization. 

If pt is used in the rate law instead of c,-, there are two ways of interpreting rt and hence kt. In the first of these, the definition of r, given in equation 1.4-2 is retained, and in the second, the definition is in terms of rate of change of p,. Care must be taken to identify which one is being used in a particular case. The first is relatively uncommon, and the second is limited to constant-density situations. The consequences of these two ways are explored further in this and the next section, first for the rate constant, and second for the Arrhenius parameters. 

The kinetics of conversion of POZ into FOZ and the Arrhenius parameters in solution can be measured by following the disappearance of a characteristic peak of the POZ, generated in situ in a solution of the olefin in liquid ethane or CS2, at low temperature. The peak at 690 cm is the most convenient one because it is relatively free from interference... 

Arrhenius parameters for nickel carbide hydrogenation 162) is close to both lines on Fig. 3. Compensation behavior for reactions on the carbide phase must include an additional feature in the postulated equilibria, to explain the removal of excess deposited carbon, if the active surface is not to be poisoned completely. The relative reduction in the effective active area of the catalyst accounts for the lower rates of reaction on nickel carbide, and the difference in the compensation line from that of the metal (Fig. 3) is identified as a consequence of the poisoning-regeneration process. After any change in reaction conditions, a period of reestablishment of surface equilibria was required before a new constant reaction rate was attained (22). 

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). 

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