OXYGEN-17 SEMIQUINONES . EFFECT OF FLUORINE SUBSTITUTION

A series of fluorinated semiquinone radicals has been studied by electron spin resonance spectroscopy. The isotropic fluorine hyperflne coupling constants, aF, for 2-fluoro-, 2,5-difluoro-, 2,3,5,6-tetrafluoro-, and 3,6-difluoro-2,5-dioxysemiquinone were found to be 3.50, 5.35, 3.95, and –3.85 G, respectively. Oxygen-17 enrichment of several radicals allowed observation of the values of aO, and these were found to differ very slightly from the values found in unfluorinated semiquinones. In addition, interactions with naturally abundant carbon-13 were examined and also found similar in magnitude to those reported for unsubstituted semiquinones. The proton coupling constants observed in the partially fluorinated radicals, however, indicated that within the ring, changes of up to 40% in spin density occur upon fluorine substitution. This is the first instance in which fluorination has been found to produce such large redistributions of unpaired electron density. © 1969, American Chemical Society. All rights reserved.