Solutions of chloranil (CA) in toluene or benzene have been oxidation potential of N is not larger than that of HB and the products 8-10 may well be formed through an ET to 3 CA. irradiated in the presence of the C 7 H 8 valence isomers homobenzvalene (HB), norbornadiene (N), and quadri-However, the pathway leading to product 3 most probably involves diradical intermediates. This should also be the case cyclane (Q). In the case of HB, the adducts 3-6 were obtained, all of them having a rearranged structure. By a for the adducts 11 and 12, which were produced upon irradiation of methyl phenylglyoxylate (PG) in the presence separate irradiation it was shown that 4 is a consecutive product of 3. The structure of 4 was established by X-ray of N. In the case of Q, an ET to 3 CA is again highly likely, followed by a combination of the radical ions to generate the diffraction analysis. These reactions are most probably initiated by an electron transfer (ET) from HB to 3 CA, zwitterion 29, which eventually collapses to produce the oxetane 8 as the sole identifiable product. The continue by bond formation between the radical ions to give the zwitterion 14, which undergoes Wagner-Meerwein photoreactions of CA with N and Q proceeded much less efficiently in acetonitrile solution. rearrangements, and are completed by ring-closure between the charged centres of the resulting zwitterions. The ralane, barbaralone, [15] and benzvalene (BV ว 2) give