Tetrahedron p. 799 - 808 (1982)
Update date:2022-09-26
Topics:
Dowd, Paul
Chow, Mudan
The energy of activation for ring-closure of ground state triplet trimethylenemethane (I) to methylenecyclopropane has been measured by following the rate of disappearance of the electron spin resonance spectrum over the temperature range - 155 deg C to - 140 deg C, in a series of frozen solid matrices.The experiments described make use of 3-methylenecyclobutanone and methylenecyclopropane as precursors to trimethylenemethane.Kinetic results obtained starting from methylenecyclopropane were most satisfactory and lead to an energy of activation for ring-closure of 7 kcal/mole.This value is significantly smaller than the approx. 20 kcal/mole barrier estimated on the basis of theoretical models.Truncation of the barrier by a tunnelling mechanism is made unlikely by the finding that trimethylenemethane-d6(I-d6) undergoes ring-closure with the same 7 kcal/mole energy of activation as the parent I.
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