The observed product ratio favoring I1 can be rationalized, at least qualitatively, in terms of less steric hindrance about the carbonyl groups with respect to solvation, fewer nonbonded hydrogen repulsions, and less ring strain. The steric hindrance about the carbonyl group in I is dramatically demonstrated by its lack of reactivity6 toward hydroxylamine. In contrast, under normal conditions the ketone I1 is easily converted to the corresponding oxime, 3. 90 % yield, m.p. 135-136"; Y N~,~~ 3226, 3125, and 1667 cm.-l. The n.m.r. spectrum shows a typical C-8 endo-proton doublet centered at T 8.72, J1 = -13 C.P.S. and J2 = -4 c.P.s., and a broad peak at T 6.74 (-0-H).We visualize the isomerization reaction as a transannularly assisted abstraction of a hydrogen atom from C-5 to form the carbanion Ia. Because of the proximity, the anion adds to the carbonyl group to form the bird-cage alkoxide anion IIIa, a transannular enolate anion, which is thermally unstable at the reaction temperature with respect to the less strained species Ia and IIa. Protonation of the anions then provides the thermodynamically controlled mixture of the ketones I and 11. No alcohol I11 could be found in the reaction products.The Crystal and Molecular Structure of Congressane, C14H20) by X-Ray Diffraction Sir :A structure analysis by X-ray diffraction of the material described in the accompanying communication by Cupas, Schleyer, and Treckerl has verified that the material is congressane (I).A fragment of a large octahedron grown from petroleum ether was mounted on the a axis and was used to take eight layers of equi-inclination Weissenberg photographs with Cu K a radiation. Visual estimates were ( I ) C. Cupas, P. von R. Schleyer, and D. J. Trecker, J . Am. Chem. SOC., 87, 917 (1965):

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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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