Hg(³P₁) photosensitized reactions of cyclopropane

Abstract

Under static conditions the major reaction product is a polymer. Polymerization is inhibited by free radical scavengers such as NO, 02, butadiene-1,3, etc. with a simultaneous large increase in propylene yields. The NO inhibited reaction affords propenaldoxime and acrylonitrile as principal products, indicating the presence of allyl radicals, and N 2 0 which is indicative of H atoms. Polymerization can also be suppressed by rapid flow: it is entirely a secondary process. The products of the flow experiments are: propylene, biallyl, allylcyclopropane, 4-methyl pentene-1, hexene-1, 2,3-dimethyl butane, CS and C9 hydrocarbons, HZ, CH*, C3Hs, and traces of bicyclopropyl. Most of the products can be accounted for by the self-scavenging of H atoms by propylene and the ensuing reactions of isopropyl and allyl radicals. The major primary step is the formation of an electronically excited cyclopropane, possibly the ground state triplet of trimethylene with a large excess of vibrational energy. The primary decomposition is retarded by pressure. O(decomp.) > 0.38, at 20 Torr, but is less than unity.

Photochemical rearrangement of an acyclic .beta.,.gamma.-unsaturated ketone to a conjugated cyclopropyl ketone. An oxa-di-.pi.-methane rearrangement

“…The direct analogy between the photochemical rearrangement of ß, -unsaturated ketone I and its 1,4diene analog II suggests similar mechanisms for the two processes (eq 1 for the ketone): (1) vinyl-carbonyl bridg-of an allyl radical to a cyclopropyl radical is the least favorable of the pathways available to radical species d. Closure of this species to give compounds I and IV would be expected to take precedence. 18 The absence of formation of a detectable amount of IV in the sensitized excitation and the effective use of a low energy sensitizer (E, 56) further indicate that an initial acyl cleavage is not likely and that 2,4 bonding between the carbonyl and vinyl groupings19 precedes a cleavage.…”