220. Influence of pressure on the Hammett reaction constant: dissociation of benzoic acids and phenylacetic acids

Fischer, Axel; Mann, B. R.; Vaughan, James R.

doi:10.1039/jr9610001093

Cited by 17 publications

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“…This assumption about kET is very reasonable for these substituted phenylacetyloxy radicals. A value of p = 0.5 has been measured (7) for the equilibrium acidities of substituted phenylacetic acids. If the substituent effect for the development of negative charge on the phenylacetyloxy radical as it is reduced to the corresponding anion is similar to this, then a p value equal to 30 mV/ u can be calculated for the reduction potentials.…”

Section: Discussionmentioning

confidence: 99%

Photolysis of the 1-naphthylmethyl ester of substituted phenylacetic acids: intramolecular charge transfer and rates of decarboxylation of arylacyloxy radicals

Hilborn¹,

Pincock²

1992

Can. J. Chem.

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. 70, 992 (1992). 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 for this decarboxylation process. The p value versus u 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-(I-naphthy1)-2-arylethane.Key words: acyloxy radical, decarboxylation, photolysis of benzylic esters.JAMES W. HILBORN et JAMES A. PINCOCK. Can. J. Chem. 70, 992 (1992). La photolyse des esters 6 et 8 dans le methanol conduit ii la formation de produits resultant ii la fois de cations et de radicaux naphtylmethyles. Pour les esters 6, la distribution des produits est independante de la nature de X, except6 lorsque X est un groupe methoxyle. On propose un mecanisme impliquant un clivage initial homolytique de la liaison carboneoxygkne dans 1'Ctat singulet excite de l'ester. Une competition entre le transfert d'electrons dans la paire de radicaux pour former la paire d'ions et la dtcarboxylation du radical arylacyloxy permet de calculer les vitesses de ce processus de decarboxylation. La valeur de p versus a s'approche de zero. Lorsque X est un groupe methoxyle, il se produit un transfert intramolCculaire d'tlectrons avec le noyau naphtalenique servant de accepteur et le fragment methoxyaromatique agissant comme donneur. Cet exciplexe se fragmente en dioxyde de carbone et I-(I-naphty1)-2-arylethane.

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Section: Discussionmentioning

confidence: 99%

Photolysis of the 1-naphthylmethyl ester of substituted phenylacetic acids: intramolecular charge transfer and rates of decarboxylation of arylacyloxy radicals

Hilborn¹,

Pincock²

1992

Can. J. Chem.

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“…For the pA's of phenylacetic acids, satisfactorjr correlations have been obtained with . [24][25] Making use of data for several insulated systems, Taft has devised a new scale, °, which differs significantly from the scale at the strongly electron-releasing end with more negative '8, e.g., °= -0.38 vs. " = -0.17 for the p-amino substituent. Making use of much the same data, Norman, et dl., have proposed still another scale, , which differs significantly from the others on the electron-withdrawing side with diminished <r's for the nitro and acyl substituents.…”

Section: Resultsmentioning

confidence: 99%

The ρ-ρ Relation and Transmission of Electronic Effects in the Reaction of Phenylacetic Acids with Diphenyldiazomethane

O'Ferrall¹,

Miller²

1963

J. Am. Chem. Soc.

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Directing and activating effects involving selenium and tellurium

Fringuelli

Taticchi

1986

PATAI'S Chemistry of Functional Groups

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220. Influence of pressure on the Hammett reaction constant: dissociation of benzoic acids and phenylacetic acids

Cited by 17 publications

References 0 publications

Photolysis of the 1-naphthylmethyl ester of substituted phenylacetic acids: intramolecular charge transfer and rates of decarboxylation of arylacyloxy radicals

Photolysis of the 1-naphthylmethyl ester of substituted phenylacetic acids: intramolecular charge transfer and rates of decarboxylation of arylacyloxy radicals

The ρ-ρ Relation and Transmission of Electronic Effects in the Reaction of Phenylacetic Acids with Diphenyldiazomethane

Directing and activating effects involving selenium and tellurium

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