TRIMETHYLENEMETHANE; ACTIVATION ENERGY FOR RING-CLOSURE OF THE DIRADICAL

Article abstract of DOI:10.1016/0040-4020(82)80160-9

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.