A product study of 1-adamantyl and 1-bicyclo[2.2.2]octyl radicals in hydrocarbon solvents. An unusually large hydrogen isotope effect

Photochemistry of Aryltert-Butyl Ethers in Methanol: The Effect of Substituents on an Excited State Cleavage Reaction

“…Photochemistry of the Adamantyl Ether 9. The adamantyl ether 9 provides a good comparison with tertbutyl ether 8j for two main reasons: (1) the chemistry of the alkyl fragment of the ether can be studied and (2) the adamantyl radical, in contrast to the tert-butyl radical, is known to be very unreactive toward disproportionation 35 by H atom donation as a consequence of the low stability of 1-adamantene. Kropp and co-workers 36 have shown that the adamantyl group can be used to study the partitioning between radical and ionic behavior in the photochemistry of phenyl thio and seleno ethers.…”

“…The adamantyl radical has been shown to be a very reactive H atom abstractor from studies on the photochemistry of azoadamantane, 19. 35 In fact, evidence was presented that the dimer 14, formed from 19, was only formed from in-cage recombination. Adamantyl radicals that escaped the cage seemed to result only in adamantane or aromatic addition products in solvents such as benzene, toluene, cyclohexane, pentane, and tertbutyl alcohol.…”

“…However, the adamantyl radical has a large isotope effect for H atom abstraction with k H /k D values of 11 (toluene) and 26 (cyclohexane) at 65°C. 35 Therefore, the adamantyl radical must be abstracting hydrogen atoms from methanol-d 4 in competition with some other nondeuterated source, probably the adamantane group of the starting ether, 9.…”

“…The products 13 , 14 , and 17 are those expected from the radical pair in methanol. The adamantyl radical has been shown to be a very reactive H atom abstractor from studies on the photochemistry of azoadamantane, 19 . In fact, evidence was presented that the dimer 14 , formed from 19 , was only formed from in-cage recombination.…”

Chloroform as a Hydrogen Atom Donor in Barton Reductive Decarboxylation Reactions

“…It is well-known that quantum mechanical tunneling effects can play an important role in reactions involving the transfer of light atoms (e.g., hydrogen atom), and this could also directly affect the patterns of reduction versus chlorination observed in the present work. Indeed, earlier work has provided evidence for tunneling effects in hydrogen abstraction reactions between the adamantyl radical and various hydrocarbon solvents. − Thus, to better delineate the contribution of tunneling in the observed product distributions, the transmission coefficients for HAT and CAT reactions were computed using multidimensional tunneling methods (see Table above), and the ratios of rate coefficients (at 333 K) for HAT versus DAT, HAT versus CAT, and DAT versus CAT are shown in Table . The contributions to these ratios (η tot ) from classical effects (η int ), variational effects (η var.…”