SURFACE PHOTOREACTIONS OF 2-BENZOYLCYCLOPENTANONES - SILICA-GEL SURFACE AS A POSSIBLE FIELD BRINGING OUT THE LATENT REACTIVITY OF DISPERSEDMOLECULES

Irradiation of 2-benzoyl- and 2-(p-methylbenzoyl)cyclopentanone (la an d Ib), which have the lowest n,pi excited states and showed no photor eactivities in inert solvents, neat or in the solid state, gave two ty pes of products on a silica gel surface; one arose from the cleavage o f the C-C bond a to the benzoyl group and the other arose from the cyc lopentanone C-1-C-2 bond cleavage. Analysis of Langmuir adsorption iso therm of la by a non-linear least-squares method revealed that 7.9 x 1 0(-4) mot of 1a was spread as a monomolecular layer over 1 g of silica gel, The photoreactivity of 1a on the surface was very sensitive to t he coverage; the efficiency of disappearance of la decreased monotonic ally from 100% at low coverages to zero at nearly 100% coverage. Close packing of molecules of 1 on the surface diminished the photoreactivi ty. A silica gel surface provided a possible dispersion field for brin ging out the latent photoreactivity of 1.