ESR, ENDOR, and ESEEM Spectroscopy Study on the Local Structure and Motion of Reactants:  Highly Selective Tunneling Radical Abstraction in a Neopentane−Ethane Mixture

Local structures and motions of radical reactants in highly selective tunneling abstraction reaction in neopentane−ethane mixture are investigated with 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 %) mixtures above 40 K react selectively with the solute C2H6 to give ethyl radicals. 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 radicals are rigidly trapped below 100 K, ethyl radicals in neopentane matrix begin to librate even at 6 K and increase the degree of motion up to 30 K. Finally, the librating motion of the ethyl radicals in neopentane matrix is vigorous above 40 K. The ethane molecule can take more favorable orientation for the hydrogen abstraction reaction by H atoms than rigid neopentane molecules by the vigorous libration motion, resulting in the selective reaction with H atoms.