Radical kinetics

Demonstrate that the variations in the rate of initiation and r are consistent with free-radical kinetics and evaluate k. ... 

Cyclopropylcarbinyl radicals (5) are alkyl radicals but they undergo rapid ring opening to give butenyl radicals." The rate constant for this process has been measured by picosecond radical kinetic techniques to be in the range of 10 M s for the parent to lO Af s for substituted derivatives. This process has been observed in bicyclo[4.1,0]heptan-4-ones. ... 

Example 13.5 Determine the instantaneous distributions of chain lengths by number and weight before and after termination by combination. Apply the quasi-steady and equal reactivity assumptions to a batch polymerization with free-radical kinetics and chemical initiation. 

Example 13.7 A 50/50 (molar) mixture of st5Tene and acrylonitrile is batch polymerized by free-radical kinetics until 80% molar conversion of the monomers is achieved. Determine the copolymer composition distribution. 

Platz J, OJ Nielsen, J Sehested, TJ Wallington (1995) Atmospheric chemistry of l,Ll-trichloroethane UV absorption spectra and self-reaction kinetics of CCljCHj and CCI3CH2O2 radicals, kinetics of the reactions of the CCljCHjOj radical with NO and NOj, and the fate of alkoxy radical CCI3CH2O. J Phys Chem 99 6570-6579. 

The major breakthrough in the development of such RsE species was achieved several years ago by Sekiguchi et al., who reported the isolation and full identification of a homologous series of (t-Bu2MeSi)3E (E = Si, Ge, Sn) radicals without Jt-bond conjugation. " All of these radicals, kinetically and thermodynamically stabilized by the bulky electropositive silyl substituents, were prepared by the same very simple and straightforward method, which clearly danonstrated the generality of this synthetic approach. 

Greiner, N.R. (1967) Hydroxyl-radical kinetics by kinetic spectroscopy. II. Reactions with C2H6, C3H8, and iso-CA IK) at 300 K. J. Chem. Phys. 46, 3389-3392. 

A major source of error in any indirect method is inaccuracy of the basis rate constants. Errors can result from determinations of rate constants by a sequence of several indirect studies or by an unanticipated solvent effect on the kinetics of a basis reaction. An error can also result in calibration of a radical clock if the requisite assumption that the clock radical will react with a rate constant equal to that of a simple model radical is not correct. Nevertheless, indirect methods in general, and radical clock studies in particular, have been the workhorse of radical kinetic determinations. 

It is with great pleasure that we dedicate this review to Dr. Keith U. Ingold, a mentor and friend and leader in the field of radical kinetics, on the occasion of his 70th birthday. 

Staffer et al. [81] have investigated the sonochemical polymerisation of both methyl methacrylate and acrylamide. No polymerisation was observed in the absence of an initiator. However in the presence of initiator and ultrasound, polymerisation conformed to the usual radical kinetics. Orszulik [82] has also been able to show that whilst polymerisation and copolymerisation of acrylic monomers did not occur in the absence of the initiator, in the presence of AZBN as initiator moderately high yields were produced after prolonged sonication (17 h). 

Typical energies of activation for propagation and termination are given in Table 6.2 and typical free radical kinetic values in Table 6.3. 

Many examples of radicals kinetically favoring addition to double bonds... 

Schindler and coworkers verified the formation of hydroxyl radicals kinetically and further RRKM calculations by Cremer and coworkers placed the overall concept on a more quantitative basis by verifying the measured amount of OH radical. An extensive series of calculations on substituted alkenes placed this overall decomposition mechanism and the involvement of carbonyl oxides in the ozonolysis of alkenes on a firm theoretical basis. The prodnction of OH radicals in solution phase was also snggested on the basis of a series of DFT calculations . Interestingly, both experiment and theory support a concerted [4 4- 2] cycloaddition for the ozone-acetylene reaction rather than a nonconcerted reaction involving biradical intermediates . 

Abbatt, J. P. D., K. L. Demerjian, and J. G. Anderson, A New Approach to Free-Radical Kinetics Radially and Axially Resolved High-Pressure Discharge Flow with Results for OH + (C2HA, C,Hx, n-C4H,(), -C5Hi2 - Products at 297 K, J. Phys. Chem., 94, 4566-4575 (1990). 

Greiner, N. R., Hydroxyl Radical Kinetics by Kinetic Spectroscopy. VI. Reactions with Alkanes in the Range 300-500 K, . /. Chem. Phys., 53, 1070-1076 (1970). 

Wallington, T. J., J. Sehested, and O. J. Nielsen, Atmospheric Chemistry of CF,C(0)02 Radicals. Kinetics of Their Reaction with N02 and Kinetics of the Thermal Decomposition of the Product CF,C(0)02N02, Chem. Phys. Lett., 226, 563-569 (1994e). 

Many examples of radicals kinetically favoring addition to double bonds over triple bonds are known.11 Yet, vinyl radical cyclization in the present procedure is initiated by the addition of a tin radical to a triple bond.12 The apparent selectivity of the tin radical for the triple bond in the presence of a double bond is, at least in some cases, a result of reversible addition to both followed by selective cyclization of the vinyl radical. ... 

Chuang, Y.-Y., Radhakrishnan, M. L., Fast, P. L., Cramer, C. J., and Truhlar, D. G. 1999. Direct Dynamics for Free Radical Kinetics in Solution Solvent Effect on the Rate Constant for the Reaction of Methanol with Atomic Hydrogen ,. /. Phys. Chem. A, 103, 4893. 

The past decade has been an extremely fruitful one in the field of quantitative free radical kinetics. Two papers can be identified as the starting point of much of this work. The first of these is the acetone photolysis study by Noyes and Dorfman1 which gave confidence to the use of acetone as a reproducible source of methyl free radicals in a fairly simple kinetic environment. The second is the study of Gomer and Kistiakow-sky2 of the absolute rate of recombination of CH3 radicals. The latter study made it possible to give absolute values for the Arrhenius parameters for the reactions of alkyl free radicals with stable molecules. It also opened the way for putting the reactions of methyl radicals with other alkyl radicals on an absolute basis. 

Peroxy radicals are intermediates in the atmospheric oxidation of air pollutants and in oxidation reactions at moderate temperatures. They are rapidly formed from free radicals by addition of 02. Free radicals in the atmosphere are quantitatively converted to R02 with a half-time of about 1 fis. The peroxy radicals are then removed by reaction with other trace species. The dominant pathways are reactions with NO and NOz. Only a few peroxy radicals have been detected with a mass spectrometer, and extensive research on these reactions has been done by UV absorption spectroscopy with the well-known and conveniently accessed band in the 200- to 300-nm region. Nevertheless, FPTRMS has been used for some peroxy radical kinetics investigations. These have usually made use of the mass spectrometer to observe more than one species, and have given information on product channels. The FPTRMS work has been exclusively on atmospheric reactions of chlorofluoromethanes and replacements for the chlorofluoromethanes. 

Hammett s correlation for rate constants of chlorinated alkanes reacting with hydroxyl radical. Experimental conditions elementary hydroxyl radical kinetic data, pH 9. 

Khursan SL, Martem yanov VS, Denisov ET (1990) Mechanism of the recombination of peroxyl radicals. Kinet Catal 31 899-907... 

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