Kinobscurinone, a benzo[b]fluorenone quinone previously reported to be
''NMR silent,'' affording neither H-1- nor C-13 NMR spectra under a v
ariety of conditions, has now been shown to exist in part as a free ra
dical under ambient conditions. The g value for kinobscurinone was fou
nd to be 2.0052; no hyperfine splitting was observed. ESR signals were
similarly observed for three other substituted benzo[b]fluorene quino
nes. (C) 1997 Elsevier Science Ltd.