Electron Spin Resonance of RĊHCOR′ Radicals in X-Irradiated Ketone—Urea Inclusion Compounds

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Abstract
Single crystals of six inclusion compounds formed between aliphatic ketones and urea were x irradiated at room temperature, and the free radicals produced were investigated by electron spin resonance. The six ketones investigated were 2‐nonanone, 6‐undecanone, 3‐tetradecanone, 2‐undecanone, 2‐dodecanone, and 3‐undecanone. The long‐lived free radicals observed in all of these compounds (RCH2ĊHCOR′) are formed by the removal of one α proton from the parent ketone. The unpaired spin density in the 2p orbital adjacent to the carbonyl group is 0.81±0.08. A contour plot of the spin density as a function of the molecular orbital parameters is given. In qualitative agreement with the ESR results, the molecular orbital methods predict the position of maximum spin density to be adjacent to the carbonyl group.