Abstract: The active radicals produced in the photochemical hydrogen abstraction reactions between benzophenone and aliphatic or aromat;c hydrocarbons have been studied by combination of spin trapping reagent 2,4, 6-tri-t-butylnitrosobenzene (TBN) by ESR spectroscopy.Results show that R₃R₂R₁Ċ reacts with TBN to form N-alkoxyanilino spin adducts, and RĊHR' reacts with TBN to form both N-alkoxyanilino and Nitroxide spin adduets.Therefore, TBN may be used for distinguishing radicals from aliphatic or aromatic hydrocarbons with and without steric hindrance.