Photochemical reduction of xanthone in an alcoholic solution flowing in a column packed with MCM-41, a mesoporous silica, was dependent on the magnetic field. The free radical intermediates were detected by the spin trapping method and the yield of spin adducts was also dependent on the magnetic field. In addition, a radicalquenching experiment was made to analyze the bulk concentrations of the free radical intermediates as functions of the magnetic field. Although these magnetic field dependencies were different from those observed in the micelle, we concluded that these observations are explained with the '' relaxation mechanism '' of the radical pair model: i.e. the intermediate radical pair in a cage has a life span comparable to or longer than the spin lattice relaxation times of these radical intermediates. The mechanism and characteristics of this cage effect in the nanotube, which is opened at the both ends, are discussed.

The structures and reactions of radical cations of prototype alkanes such as ethane, propane, isobutane, neopentane, etc. produced in SF6 and in other halocarbon matrices irradiated at 4 K have been extensively studied by ESR. The geometrical structures as well as the unpaired electron orbitals of these cations are unequivocally characterized based on the simple symmetry considerations as well as the INDO MO calculations. The ESR hyperfine coupling constants determined for these cations as well as their deuterated homologs give conclusive evidence for the interpretations. The unpaired electron in linear alkane cations is delocalized over the in-plane C–H and C–C σ bonds forming delocalized σ radicals, whereas that in highly branched alkane cations is more confined to one of the C–C bonds forming localized σ radicals. The H1s spin density, giving a large hyperfine coupling in the linear alkane cations, is largely contributed from a direct participation of the C–H bond in the unpaired electron orbital, whereas that in the highly branched alkane cations is due to mainly hyperconjugation. The alkane cations undergo two types of reactions: one is deprotonation to form neutral alkyl radicals in SF6 and in CFCl2CF2Cl and the other is the H2 and CH4 elimination to form olefinic π cations in CFCl3. Based on the matrix effects on the structure of propane and isobutane cations, the site preference in forming alkyl radicals, and other observations, it is concluded that the alkane cations undergo reactions through the breakage of the bond in which the unpaired electron is highly populated.

E.s.r. evidence has been obtained that cyclopropane cations exhibit a static distortion from Dgh to C2" symmetry in a matrix at 4.2 K; the 3e' (D3h) highest occupied degenerate orbital splits into 6a, and 3bl (C2") orbitals and the unpaired electron occupies 6a1, giving dominant spin densities on the two basal carbon atoms. Recentlywe have found that C2H6+, a Jahn-Teller active molecule, trapped in SF, shows a reversible temperature t Preliminary results were presented at the 46th Autumn Annual Meeting of the Chemical Society of Japan, 3rd October, 1982, Niigata, Abstract p. 13; details were presented at the 21st E.s.r. Symposium, 26th October, 1982, Tsukuba, Abstract p. 48.change which may be ascribable to static and dynamic Jahn-Teller effects? Cyclopropane (cyclo-C3H6) with Dab symmetry possesses a degenerate highest occupied orbital (3e') so that cyclo-C,H,+ is also a Jahn-Teller active molecule. Recently Shida and CO-WOrkerS2 have observed the e.s.r. spectrum Of cyc10-C3H6f produced in CFC13 at 77 and have explained the extremely small hyperfine couplings giving an

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