Chemical activation study of the reactions of methylene with oxetan and 3,3-dimethyloxetan

Abstract

Methylene (singlet) formed by the photolysis of ketene (313 nm) reacts with oxetan to yield 2-methyl- and 3-methyloxetans by insertion in the C—H bonds and probably also tetrahydrofuran. These products are formed chemically activated and undergo unimolecular decomposition unless collisionally stabilized. Using perfluoropropane as the bath gas, the results obtained with 2-methyloxetan have been interpreted using RRKM theory and a step-ladder model with a most probable step size of ca. 9 kJ mol^–1. Using 206 nm radiation yields methylene with excess energy, some of which is still present when it reacts, and results in the production of 2-methyloxetan with an average lifetime approximately one-half that of the energised molecule produced when 313 nm radiation is used.

Similarly methylene reacts with 3,3-dimethyloxetan to yield chemically activated 3-ethyl-3-methyloxetan and 2,3,3-trimethyloxetan. A third compound tentatively identified as 3,3-dimethyltetrahydrofuran is also formed. The decomposition of these 3 molecules has been followed and in the case of the ethylmethyloxetan the average energy transferred in collision with 3,3-dimethyloxetan has been found to be ca. 6.5 kJ mol^–1.

Some deductions can be made about the Arrhenius parameters for the thermal decomposition of the (as yet unreported) trimethyloxetan and the dimethyltetrahydrofuran.