Bruce E. Smart

Fluorine substituent effects (on bioactivity)

Abstract The characteristic effects of fluorine and fluoroalkyl substituents on the physico-chemical properties of molecules that are important to biological activity of fluorinated compounds are highlighted. The influence of fluorination on acidity, hydrogen-bonding, and lipophilicity that affect compound absorption and distribution is described. The current perspectives on fluorine steric interactions and the controversial role of hydrogen-bonding involving the CF bond are discussed.

Electrophilic reactions of fluorocarbons under the action of aluminum chlorofluoride, a potent Lewis acid

Abstract A new Lewis acid — aluminum chlorofluoride — was demonstrated to be an effective catalyst for the isomerization of fluoroolefins, polyfluorinated epoxides and cyclopropanes. At ambient temperature this catalyst converts perfluorobutadiene-1,3 into perfluorobutyne-2 and perfluoro(4-methylpentene-2) into perfluoro(2-methylpentene-2) in nearly quantitative yield. At 100 °C, aluminum chlorofluoride causes the cleavage of perfluorinated tertiary amines.

ISOMERIZATION OF HALOPOLYFLUOROALKANES BY THE ACTION OF ALUMINUM CHLOROFLUORIDE

Abstract A combination of aluminum chlorofluoride (ACF) /fluoroolefin is an effective catalytic system for isomerization of vic-dichloroperfluoroalkanes into gem-isomers. For example, the isomerization of 1,2-dichloro-F- propane in the presence of catalytic amounts of ACF and hexafluoropropene proceeds at 130°C giving 2,2-dichloro- F-propane in high yield. This catalytic system is also effective for converting cyclic 1,2-dichloro-F-cycloalkanes into 1,1-dichloro-F-cycloalkanes. Dibromo-F-alkanes are more reactive and rearrange under the action of ACF alone at 25—100°C. Primary monoiodo- and monobromo-F-alkanes in the presence of ACF are converted into secondary isomers in moderate yields.

Bond energies in organofluorine systems: applications to Teflon® and fullerenes

Abstract Computational chemistry methods have been used to calculate bond energies in organofluorine compounds. The bond strengths in models of Teflon® have been calculated by using ab initio molecular orbital theory. The CF bond strengths fall in the expected ranges. The CC bond strengths are much higher than those in the corresponding hydrocarbon model. The CF bond strengths in the C60F, C60F2 and C70F were calculated at the non-local density functional theory level. These bond strengths are much weaker than those in saturated organofluorine compounds.

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.

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.

The effect of fluorine substitution on the structure of oxiranes and on the energetics of the oxiranylcarbinyl radical ring opening

Abstract Fluorine substituent effects on the structure of oxirane and on the kinetic behavior of oxiranylcarbinyl radicals, as determined by DFT calculations, have been found to be similar to those observed for the analogous fluorinated cyclopropylcarbinyl radical systems. A structural and energetic analysis showed that a stereoelectronic effect involving preferential interaction of the semi-occupied atomic orbital of the radical with the weaker ring bond is the major factor that contributes to the regiochemistry of the ring opening of fluorinated oxiranylcarbinyl radicals. With low and potentially zero activation barriers, 3,3-difluorooxiranylcarbinyl radical and cation undergo ring opening with CO bond cleavage and CC cleavage, respectively.