1976 Volume 49 Issue 12 Pages 3376-3381
The ENDOR spectra of ten kinds of phenylgalvinoxyl derivatives in solution have been observed, and the hyperfine splitting constants have been determined. The formally equivalent four meta ring protons of the galvinoxyl skeleton in the phenylgalvinoxyl radical become magnetically nonequivalent in two groups of two. This behavior may be explained by assuming that splittings arising through pure spin polarization, or through mixed hyperconjugation and spin polarization, are different for syn and anti meta ring protons of the phenylgalvinoxyl radical. A similar effect has been observed in the ENDOR spectra of other phenylgalvinoxyl derivatives. In radicals with a large substitution group at the meta or para position of the phenyl ring, the galvinoxyl skeleton twists unsymmetrically on either side; thus, all or three among the four meta ring protons become magnetically nonequivalent. The solvent dependence of the ENDOR spectra of the phenylgalvinoxyl radicals constituted strong evidence for the importance of the solvent in fixing the conformation and symmetric property of the radical molecules. The proposed analyses of the ENDOR spectra were also supported by the McLachlan Molecular Orbital calculations.
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