Kinetic effects of fluorine substituents in free-radical chemistry. Hydrogen-atom abstraction reactions of perfluoro-n-alkyl radicals

Cyclizations of 5-Hexenyl, 6-Heptenyl, 7-Octenyl, and 8-Nonenyl Radicals. The Kinetic and Regiochemical Impact of Fluorine and Oxygen Substituents

“…It was then fortunately possible to devise a good competition experiment using pentafluorostyrene in competition with (TMS) 3 SiH, wherein the rate constant k H = 5.2 (±0.6) × 10 7 M -1 s -1 was obtained in a manner described previously . This value is virtually identical to that for the analogous H-transfer to a perfluoro- n -alkyl radical [ k H = 5.1 (±0.5) × 10 7 M -1 s -1 ] …”

Cyclization reactivities of fluorinated hex-5-enyl radicals

“…All values of k H for the various per-and partially-fluorinated radicals, except for that used in determination of the rates of cyclization of 2k, had been previously determined, and these values are also given in Table 1. [14][15][16][17] The value of k H for the reduction of 1,1,2,2-tetrafluoroalkyl radicals by (TMS) 3 SiH was determined in this work, by the usual method, 16 and its value is also given in Table 1. With all required values for k H being available along with the determined ratios of k C5 and k C6 to k H , it was therefore possible to calculate the values for k C5 and k C6 for each of the hex-5-enyl radical systems, 2b-m.…”

Absolute Rates of Intermolecular Carbon−Hydrogen Abstraction Reactions by Fluorinated Radicals

“…Thus rate constants for hydrogen abstraction by perfluoroalkyl radicals from relatively electropositive atoms such as Sn, Si, or even carbon are much larger than those of the analogous alkyl radicals. For example, the rate constants for hydrogen abstraction from n -Bu 3 SnH and Et 3 SiH by n -R f • are 85 and 714 times larger, respectively, than by n -R • . − With a preliminary indication of molar rate constants in the range of 10 4 −10 5 M -1 s -1 for hydrogen transfer from relatively good C−H donors such as tetrahydrofuran (THF), we considered it important to evaluate and quantitate the bimolecular C−H donor ability of a broad range of functionalized organic compounds having C−H bonds in a variety of molecular environments. In commercial polymerizations, H-transfer from C−H bonds of surfactants and initiators can be the main source of polymer inhibition or low molecular weight product as a result of terminating chain transfer .…”