Rate constants for hydrogen abstraction from alkoxides by a perfluoroalkyl radical. An oxyanion accelerated process.

A combination of laser flash photolysis and competitive kinetic methods has been used to measure the absolute bimolecular rate constants for hydrogen atom abstraction in water from a series of fluorinated alkoxides and aldehyde hydrates by the perfluoroalkyl radical, *CF2CF2OCF2CF2SO3- Na+. The bimolecular rate constants observed for the beta-fluorinated alkoxides were in the 10(5) M(-1) s(-1) range, such rates representing enhancements (relative to the respective alcohols) of between 100 and almost 1000-fold, depending on the reactivity of the alkoxide. Likewise, the monobasic sodium salts of chloral and fluoral hydrate exhibit similar rate enhancements, relative to their respective hydrates.

Large primary kinetic isotope effects in the abstraction of hydrogen from organic compounds by a fluorinated radical in water.

Isotope effects have been measured for the abstraction of hydrogen from a series of organic substrates by the perfluoro radical, Na+ -O3SCF2CF2OCF2CF2*, in water. Both primary and secondary deuterium isotope effects were measured, with the primary isotope effects ranging in value from 4.5 for isopropanol to 19.6 for acetic acid. The values for the alpha- and beta-secondary deuterium isotope effects were 1.06 and 1.035, respectively. It was concluded that tunneling contributes significantly to the production of the observed, large primary kinetic isotope effects in these C-H abstraction reactions.

Absolute rate constants for some hydrogen atom abstraction reactions by a primary fluoroalkyl radical in water.

A combination of laser flash photolysis and competitive kinetic methods have been used to measure the absolute bimolecular rate constants for hydrogen atom abstraction in water from a variety of organic substrates including alcohols, ethers, and carboxylic acids by the perfluoroalkyl radical, *CF(2)CF(2)OCF(2)CF(2)SO(3)(-) Na(+). Comparison, where possible, of these rate constants with those previously measured for analogous reactions in the non-polar organic solvent, 1,3-bis(trifluoromethyl)benzene (J. Am. Chem. Soc, 1999, 121, 7335) show that the alcohols react 2-5 times more rapidly in the water solvent and that the ethers react at the same rate in both solvents. A transition state for hydrogen abstraction that is more reminiscent of an "intimate ion pair" than a "solvent separated ion pair" is invoked to explain these modest solvent effects.

Use of gas-phase (1)H NMR to determine the kinetics of unimolecular rearrangement of 2,2-dichloro-1-methylenecyclopropane and the bimolecular dimerization of (dichloromethylene)cyclopropane.

Gas-phase (1)H NMR analysis has been applied to investigate the kinetics of the unimolecular rearrangement of 2,2-dichloro-1-methylenecyclopropane (1) to (dichloromethylene)cyclopropane (2) [k(1) = 7.9 x 10(12) exp(-34.4 +/- 0.6 kcal mol(-1)/RT)], as well as for the subsequent second-order dimerization of 2 [k(2) = 2.4 x 10(6) exp(-18.5 +/- 1.1 kcal mol(-1)/RT)] to form 7,7,8,8-tetrachlorodispiro[2.0.2.2]octane (3)