- Photolysis of the 1-naphthylmethyl ester of substituted phenylacetic acids: intramolecular charge transfer and rates of decarboxylation of arylacyl radicals
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The photolysis of esters 6 and 8 in methanol leads to products resulting from both naphthylmethyl cations and radicals.The product distribution is nearly independent of X for the esters 6 except when X equals methoxy.A mechanism involving initial homolytic cleavage of the carbon-oxygen bond in the excited singlet state of the ester is proposed.Competition between electron transfer in the radical pair to form the ion pair and decarboxylation of the arylacyloxy radical allows calculations of the rates of this decarboxylation process.The ρ values versus ? is close to zero.When X equals methoxy, intramolecular electron transfer occurs with the naphthalene ring serving as the acceptor and the methoxyaromatic as the donor.This exciplex fragments to carbon dioxide and 1-(1-naphthyl)-2-arylethane. Key words: acyloxy radical, decarboxylation, photolysis of benzylic esters.
- Hilborn, James W.,Pincock, James A.
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p. 992 - 999
(2007/10/02)
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- Photolyses of (3-Naphthoxypropyl)-, (4-Naphthylbutyl)-, and (4-Naphthyl-4-oxobutyl)cobaloxime
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The cobalt-carbon bond of the titled compounds is photochemically cleaved to generate an organoradical and a cobaloxime(II) radical pair. 3-(1- or 2-naphtoxy)propyl, 4-(1- or 2-naphthyl)butyl, and 4-(1-or 2-napthyl)-4-oxobutyl radicals thus formed undergo three types of reactions: (a) hydrogen abstraction to give a saturated terminal, (b) hydrogen elimination to give a terminal olefin, and (c) substitution on the naphthalene ring.In benzene and radicals follow process b exclusively (the radicals from (3-(2-napthoxy)propyl)cobaloxime (1a), (3-(1-napthoxy)propyl)cobaloxime (2a), and (4-(1-napthyl)butyl)cobaloxime (2 b)) or preferentially (the radicals from (4-(2-napthyl)butyl)cobaloxime (1 b), (4-(2-napthyl)-4-oxobutyl)cobaloxime (1c), and 4-(1-napthyl)-4-oxobutyl)cobaloxime (2c)).In chloroform, process a becomes important to the extent as the sum of the other two processes.In water-acetonitril (4:1), process c becomes important and even takes precedence of others for the radicals from 1b and 1c.This feature is accounted for by the folding of the side chain of hydrophobic radicals.Encapsulation of the radicals in β-cyclodextrin stimulates process c except for the case of the radical from 2c.In the case of cobaloxime 2c, α-cyclodextrin does not effect the partition process of the intermediate radical.This feature is accounted for by the shallow inclusion of the radical due to the hydrogen bonding as depicted in Figure 1d.
- Tada, Masaru,Hiratsuka, Mitsunori,Goto, Hiroyuki
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p. 4364 - 4370
(2007/10/02)
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