Spin Trapping by Use of Nitroso-Compounds. VII. β-Fluorine Splitting Constants in Nitroxides

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Abstract
Hyperfine splitting constants of β-fluorine atoms in aryl perfluoroalkyl nitroxides, ArN(Rf)O·, where Ar= 2,4,6-tri-t-butylphenyl, phenyl, pentafluorophenyl, and 2,3,5,6-tetramethylphenyl and Rf=trifluoromethyl, pentafluoroethyl, and heptafluoroisopropyl were explored. The temperature dependence of hyperfine splitting constants was studied in the cases of 2,4,6-tri-t-butylphenyl and pentafluorophenyl nitroxides. In the former nitroxides the conformation of β-fluorine atoms are rigid and dihedral angles between the Cβ–F bonds and pz orbitals are 30 and 0° when perfluoroalkyl groups are ethyl and isopropyl, respectively. The conformational dependence of β-fluorine splitting constants are discussed, and it is concluded that the cos2θ law, aβF=(B0+Bcos2θ)ρπ, is also applicable to β-fluorine splitting constants in a series of nitroxides. The values of B0 and B seem significantly dependent on the compound.

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