Benzophenone‐sensitized photopolymerization of methyl acrylate was shown to be remarkably enhanced by the addition of small amounts of triethylamine. This was attributed to the efficient formation of an electron‐transfer complex between photoactivated benzophenone and ground‐state amine. Ketyl and amine free radicals derived from this complex were postulated to be the chain‐initiating species. Quantum yield experiments indicated that methyl acrylate itself was also a quencher of the benzophenone triplet state.

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When heated, neat or in hydrocarbon solvent, cis,trans-\,3-cyclooctadiene underwent both dimerization and isomerization. The structures of the 2 + 2 cyclodimers were assigned as the trans.cis, trans.trans, and cis,cis dimers. The ratio of the three dimers was found to be independent of the reaction temperature. The reaction followed good second-order kinetics and has /í* = 19 kcal/mol and 5+ = -10 eu. The results have been rationalized on the basis of a stepwise mechanism for dimer formation.he concerted, suprafacial, thermal fusion of two olefins to form a cyclobutane ring is a symmetryforbidden process.4 In accord with this prediction, thermal "1,2" cycloadditions of simple olefins have been shown to involve diradical intermediates.5 Thermal cycloaddition can, in theory, proceed in a concerted symmetry-allowed fashion by a (tt2s + ir2a) combination of the two 7 bonds.4 The high degree of stereospecificity in the 2 + 2 cycloaddition of olefins with alienes,6-12 ketenes,13-19 and reactive isocyanates20'21 points toward the possibility that these reactions are concerted. It appears that a cumulative -bond system can function more readily as a Tr2a donor than an isolated double bond. Orbital symmetry theory applied to the concerted fragmentation of cyclobutane demands that the process occur via the (

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spectrum of I had a quartet at 4.62,12 a singlet at 8.51, and a doublet at 8.60, which partially overlapped the singlet. These absorptions are assigned to the methine, gem-dimethyl, and methyl protons, respectively, of 2methylbutene-2 ozonide. The methyl:methine peak area ratio was 9.4:1. The spectrum of II has a triplet at 5.13, a multiplet at 8.56, a singlet at 8.83, and a triplet at 9.30. These are assigned to the methine, methylene, gem-dimethyl, and methyl protons, respectively, of 2-methylpentene-2 ozonide. The integrated areas were 1:8:3.16 for methine:gem-dimethyl plus methylene: methyl. Yields of the ozonides were 2.09, 2.22, 4.92, 2.0, and 2.06 mmoles, respectively, for the ozonides of butene-2, 2-methylbutene-2, pentene-2, 2-methylpentene-2, and hexene-3 (total yield of ozonides = 21.6%).We are presently investigating the possibility of obtaining ozonides from the remaining unobserved zwitterion-carbonyl combination, that is, the reaction of ketonic zwitterions with simple ketones.Acknowledgment. L. D. L. wishes to thank the Director of the Rubber and Plastics Research Association of Great Britain for a 1 year leave of absence, during which time this work was carried out.(12) All n.m.r. results are reported as -values with tetramethylsilane as external standard.