Rates of 1,5-hydrogen abstraction in 1,1,2,2-tetrafluoro-n-pentyl and 1,1,2,2,3,3-hexafluoro-n-pentyl radicals

A new competitive kinetic method to obtain the relative rates of intramolec ular hydrogen abstraction versus intermolecular deuterium abstraction has b een developed and used to measure the rates of the relatively slow unimolec ular 1,5-hydrogen abstractions by 1,1,2,2-tetrafluoroalkyl (XCH2CH2CH2CF2CF 2*) and 1,1,2,2,3,3-hexafluoroalkyl (XCH2CH2CF2CF2CF2*) radicals. Substitue nts at the site of C-H abstraction (X = CH3O-, CH3S-, CH3-; C6H5-, CH3C(O)O -) have only a moderate effect, with the rate constants for 1,5-shifts in t he 10(3) s(-1) range. Values of k(H) and k(D) for bimolecular hydrogen/deut erium transfer from t-BuMe2SiH(D) and Me3SiSiMe2H(D) are reported along wit h measures of side-chain H transfer from the deuterated silanes.