The H/(CH₃)₃SiH/C₂H₄Reaction System and the Addition of (CH₃)₃Si to Ethene. An End-Product Study

Abstract

Me3Si and C2H5 radicals have been generated by the reaction of H atoms with mixtures of Me3SiH and C2H4 and the subsequent reactions studied by end-product analysis. The primary radicals undergo self- and cross-combination and disproportionation reactions. The Me3Si radical also adds to the C2H4, generating another radical, Me3SiCH2CH2. This radical in turn undergoes a variety of self- and cross-combination as well as disproportionation reactions with all the radicals present. A number of relative rate constants were extracted from the data. In particular the ratio k(H + Me3SiH)/k(H+C2H4) was found to be in good agreement with recent absolute determinations of these two rate constants. For the addition reaction we obtained the relative rate constant k(Me3Si + C2H4)/k 1/2(2Me3Si) = (8.7 ± 0.2) × 10-10 cm3/2 s-1/2 at room temperature. From studies in the temperature range 300−470 K the following values of the Arrhenius parameters for the addition reaction were obtained: 11.6 ≤ E a/kJ mol-1 ≤ 14.1 and 7.1 × 10-13 ≤ A/cm3 s-1 ≤ 1.9 × 10-12. In addition, it was found that alkyl and silyl radicals closely obey the geometric mean rule and that disproportionation reactions between alkyl and silyl radicals are of only minor importance. The reactivity of the silyl radical is much higher than that of the alkyl radical in adding to C2H4, and this can be explained in terms of polar effects.

Polarity-Mismatched Addition of Electrophilic Carbon Radicals to an Electron-Deficient Acceptor: Cascade Radical Addition–Cyclization–Trapping Reaction

“…Carbon radicals having electron-withdrawing groups possess electrophilic character . We next studied the reaction of 1 with the moderately electron-deficient radicals derived from ICH 2 CO 2 Et, ICH 2 CN, and BrC(CO 2 Et) 2 Me (Scheme ).…”

Kinetics of the Addition of Olefins to Si-Centered Radicals: The Critical Role of Dispersion Interactions Revealed by Theory and Experiment

“… a Values are represented as log 10 ( k ). The mean absolute error (MAE) and the mean error (ME) for each method are also shown. Sources of experimental data are. b Reference . c Reference . d Reference . e Reference and this work. …”

“…Also included are calculated results for the addition of small olefins to methyl, tert -butyl, and silyl radicals, where dispersion is expected to have a smaller effect due to the smaller molecular size. Experimental rate constants for these additional reactions were taken from literature sources. − All of the rate constants are expressed as log 10 ( k ). The mean error (ME) and mean absolute error (MAE) in the rate constants are reported and are also expressed in logarithmic units.…”

Free-Radical Carboalkynylation and Carboalkenylation of Olefins

“…Multicomponent reactions may offer an attractive solution, extending the nature of the fragments that may be added onto the olefinic backbone. Multicomponent processes rely on the matched polarity between the different partners . The free-radical addition onto an electron-rich olefin thus implies that an electrophilic radical component is added first on the olefin, affording a nucleophilic radical intermediate that should in turn be trapped by an electrophilic partner.…”