ESR, ENDOR, and ESEEM spectroscopy study on the local structure and motionof reactants: Highly selective tunneling radical abstraction in a neopentane-ethane mixture

Local structures and motions of radical reactants in highly selective tunne ling abstraction reaction in neopentane-ethane mixture are investigated wit h CW-ESR, ENDOR, and ESEEM spectroscopy at different temperatures. H atoms produced by the radiolysis of neo-C5H12 in the neo-C5H12-C2H6 (2 mol %) mix tures above 40 K react selectively with the solute C2H6 to give ethyl radic als. The selective reaction is suppressed below 30 K. The local structures of neopentane matrix around neopentyl and ethyl radicals are approximately the same in the temperature range from 4.4 to 45 K. Although neopentyl radi cals are rigidly trapped below 100 K, ethyl radicals in neopentane matrix b egin to librate even at 6 K and increase the degree of motion up to 30 K, F inally, the librating motion of the ethyl radicals in neopentane matrix is vigorous above 40 K. The ethane molecule can take more favorable orientatio n for the hydrogen abstraction reaction by H atoms than rigid neopentane mo lecules by the vigorous libration motion, resulting in the selective reacti on with H atoms.