Adducts of group IVB radicals with sulphur-containing diaryl ketones

The hyperfine splitting constants for the paramagnetic adducts of ·MR3 radicals (M = Si, Ge, or Sn) with some dithienyl and bisthienothienyl ketones, benzophenone, and fluorenone are reported and compared with those for the corresponding diarylhydroxymethyl radicals. From the results, and with the aid of INDO calculations, it has been found that in the former derivatives the O-M bond eclipses the 2pz orbital of the carbonyl atom, at variance with the hydrogen adducts, which exhibit practically planar conformations. Barriers to rotation of the OH group in benzophenone and fluorenone derivatives have been determined from the temperature dependence of the aH^OH splitting and are 5.1 and 6.5 kcal mol ^-1, respectively.