Surface photochemistry: ¹³C enrichment by photolysis on silica gel

Abstract

The enrichment of the 13C isotope by partial photolysis of dibenzyl ketone on silica gel has been demonstrated. The 13C enrichment is substantial and is parallel to the increase in the probability of geminate radical recombination on a silica surface as compared with that in solution. A substantial 13C enrichment was also observed for the rearranged starting material, 1-phenyl-4′-methylacetophenone. The single-stage isotope separation factors are different for the two ketones although both are isomers derived from the same benzyl–phenylacetyl radical pairs.

Templation of the Excited-State Chemistry of α-(n-Alkyl) Dibenzyl Ketones: How Guest Packing within a Nanoscale Supramolecular Capsule Influences Photochemistry

“…Such a large cage effect on the secondary radical pair although noteworthy is not unprecedented in an organized assembly. Similar large cage effect has been noted earlier in micelles, zeolites, and crystals. , Lack of formation of AA and BB suggests that the capsular assembly is stable in the time scale of the lifetime of the secondary radical pair . The structures of the host−guest complexes shown in Figure account for the presence of cage effect and formation of AB and rearranged AB products.…”

“…Detailed studies have revealed that the changes in product distribution in organized assemblies are attributable to the restriction on the translational mobility (diffusion) of the primary and secondary radical pairs. Photochemistry of dibenzyl ketones has been investigated in organized assemblies such as micelles, cyclodextrins, and zeolites and in the crystalline state, and a common thread in these processes is the enhanced formation of 3 with respect to 7 and 8 (Scheme ) . Uniquely, in some of these confined media rearrangements, product 9 was obtained in less than 10% yield .…”

“…One of the most interesting features within the capsule is the formation of the rearrangement product(s) of the starting ketone. Such products are formed in less than 10% yield in micelles and zeolites and are not formed in crystals. , Even more fascinating is that the methyl-, ethyl-, and propyl-substituted dibenzyl ketones yield mostly one rearrangement product ( 10 ), whereas butyl- and pentyl-substituted dibenzyl ketones give the two rearrangement products 9 and 10 , and hexyl-, heptyl-, and octyl-substituted dibenzyl ketones do not photorearrange. Formation of 10 as the major product from methyl-, ethyl-, and propyl-substituted dibenzyl ketones is consistent with the expectation that the alkyl-substituted α-C−C bond would cleave more readily than the unsubstituted one .…”

Colour stabilisation of wood composites using polyethylene glycol and melamine resin

“…Therefore, H-abstraction, energy transfer (singlet oxygen formation (Beyer et al 1995)) and oxygen diffusion are hindered. Moreover, if the α-cleavage of lignin is reduced as well, the net yield of the process is determined by the diffusion of radicals out of the cage (Johnston and Wong 1984). In this study, the influence of melamine resins and PEG as H-donors on the degradation of wood and wood composites was investigated .…”

Magnetic Field Effects on the Dynamics of Radical Pairs: The Partition Effect in Vesicles

“…Radical reactivity in organized environments can be different from that observed in homogeneous solutions, and understanding these differences is of prime importance to establish how radicals interact with biological systems. The dynamics of radical pairs has been extensively studied in organized structures, such as micelles, microemulsions and solid supports including silica gel and zeolites (1)(2)(3)(4)(5)(6)(7)(8). However, only limited studies have been performed in biological systems (9)(10)(11)(12)(13)(14)(15) of which vesicles (16) are mimetic systems for cell membranes.…”