IMINOXY RADICALS DERIVED FROM BENZOCYCLOHEPTENONE AND HETEROCYCLIC-ANALOGS

alpha-Keto-iminoxy radicals derived from benzocycloheptenone and heter ocyclic analogs have been prepared in situ by the reaction of nitrogen dioxide with the parent ketones and their ESR spectra have been inter preted. While the radical I (the E isomer) of 2,3-dihydro-1-benzoxepin -5(4H)-one resembles similar six-member ring radicals in its proton hy perfine splitting (hfs) constants, the radicals II, III and IV (the E isomers) originating from 6,7,8,9-tetrahydro-5H-benzocyclohepten-5-one , 2,3-dihydro-1-benzothiepin-5(4H)-one and 2,3-dihydro-1-benzothiepin- 1,1-dioxide-5(4H)-one respectively, present unusually low alpha-syn pr oton hfs constants. This fact was interpreted as being due to higher t orsion angles permitted in seven-member rings as compared with six-mem ber ones. The new data obtained for this region of conformational spac e complete the experimental mapping of spin densities in iminoxy radic als and - in connection with calculated data - lead to a coherent mode l of spin density transmission mechanisms in sigma-radicals.