PHOTOLYSIS OF MATRIX-ISOLATED CYCLOPROPYLIDENE KETENE - KINETIC AND THEORETICAL-STUDIES OF THE CYCLOPROPYLIDENE FORMATION

Cyclopropylidene ketene 2 is generated by ultraviolet irradiation (lam bda greater than or equal to 230 nm) of cyclopropanecarbonyl chloride isolated in argon matrices at 15 K. FT-IR spectra of the primary photo lysis products (2 and HCl) trapped in the same cage show the formation of molecular complexes. The HCl stretching mode observed at 2793.5, 2 739 cm(-1) is shifted to 61 cm(-1) below the frequency of monomeric HC l (2888.0, 2863.5 cm(-1)) in argon matrix. Irradiation of 2 at lambda greater than or equal to 230 nm induces reversible formation of CO and of a new transient assumed to be cyclopropylidene 3. This carbene rea cts with HCl trapped in the same cage or gives 1,2-propadiene by intra molecular rearrangement. The kinetic data show that the rate constant of 1,2-propadiene formation is twice as large as that of cyclopropyl c hloride formation. To account for the results of matrix isolation expe riments the photodissociation of the cyclopropylidene ketene was model ed by ab initio calculation using 6.31G and ''mini'' Huzinaga basis s ets.