A Large Isotope Effect on Formation of Tetramethylethylene Cations in γ-Irradiated 2,3-Dimethylbutane at 77 K. Tunneling of H2 Molecule

Article abstract of DOI:10.1021/j100093a016

The significant isotope effect on hydrogen elimination reaction from 2,3-dimethylbutane (h-DMB) cations was studied by ESR at 77 K.When a h-DMB-SF6 (0.6 mol percent) mixture is γ-irradiated at 70 K, h-DMB⁺ ions in addition to h-DMB radicals are produced.When the irradiated mixture is stored at 77 K for 10 min, tetramethylene (TME) cations are produced by H2 elimination from h-DMB⁺ ions.The rate constant for the H2 elimination reaction was measured as 1.1*1E-3 S^-1 at 77 K.When a 2,3-dimethylbutane-2,3-D2 (d-DMB)-SF6 (0.6 molpercent) mixture is γ-irradiated at 70 K and then stored at 77 K, TME⁺ ions are scarcely produced upon the storage of the irradiated mixture at 77 K even for 5 days.The rate constant for the D2 elimination reaction from d-DMB⁺ ions was measured as 6.5*1E-8 s^-1, which is much smaller than the rate constant for the H2 elimination reaction.The significant isotope effect on the reactions was explained in terms of a model of the tunnaeling elimination of a hydrogen molecule from a DMB⁺ ion.