The cyclopropylmethyl free-radical clock.  Calibration for the 30-89.degree. C range

Mathew, Lata; Warkentin, John

doi:10.1021/ja00285a016

Cited by 75 publications

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“…The cyclopropyl methyl radical has been estimated to open with a rate constant of 2.1 X 10' s-' at room temperature (4,5). If the methyl group is substituted, as in the cyclopropylethyl radical, then the extra stabilization slows the rate of opening to a value estimated as 2 X lo7 s-' (9, 10).…”

Section: Discussionmentioning

confidence: 99%

“…Biradicals 4 and 5 can cyclize to 8 while 6 and 7 can close to 9. The biradicals 4 and 7 contain a cyclopropylalkyl radical that is known (5) to ring open rapidly to a homoallylic radical as shown for the formation of 10 and 11 from 4 and 7, respectively. If double bond geometry is correct in 10 and 11 then they can close to 12 and 13, respectively.…”

Section: Introductionmentioning

confidence: 99%

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Radical clocks as probes of 1,4-biradical intermediates in the photochemical cycloaddition reactions of 2-cyclopentenone with alkenes

Rudolph¹,

Weedon²

1990

Can. J. Chem.

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ANDREAS RUDOLPH and ALAN C. WEEDON. Can. J. Chem. 68, 1590 (1990). The products of the photochemical reaction of 2-cyclopentenone with 1,6-heptadiene and with vinylcyclopropane have been examined. With 1,6-heptadiene the products were cyclobutanes, which arise from 2 + 2 photocycloaddition between the cyclopentenone carbon-carbon double bond and one of the two terminal double bonds of the heptadiene. The 1,4-biradical that is an intermediate in this reaction contains a derivative of a 1-hexenyl radical; no products derived from cyclization of this intermediate to a cyclopentylmethyl radical were observed. With vinylcyclopropane some of the products isolated also arose from 2 + 2 photocycloaddition; in addition, comparable quantities of products resulting from rearrangement of the intermediate 1,4-biradical were obtained. In this case the initially produced intermediate 1,4-biradical contains a cyclopropylmethyl radical that can rearrange to a homoallylic radical; the products isolated were derived from intramolecular disproportionation in the new 1,7-biradical containing the homoallylic radical. The rate constant for the rearrangement of the cyclopropylmethyl radical to the homoallylic radical is known and was used as a clock to estimate the lifetime of the initially produced 1,4-biradical. The value estimated is of the order of 50 ns. The structures of the products indicate that the initial bonding between the excited cyclopentenone and vinylcyclopropane takes place at both the a-position and the P-position of the enone and not exclusively at the a-position as a recent report claims.Key words: enone photocycloaddition, 1,4-biradicals, radical clocks.ANDREAS RUDOLPH et ALAN C. WEEDON. Can. J. Chem. 68, 1590 (1990) On a examink la nature des produits de la rCaction photochimique he la cyclopent-2-&none avec I'hepta-1,6-dikne et avec le vinylcyclopropane. Avec l'hepta-I ,6-dikne, les produits sont des cyclobutanes qui proviennent d'une photocycloaddition 2 + 2 entre la double liaison carbone-carbone de la cyclopentknone et l'une des deux doubles liaisons terminales de I'heptadikne. Le 1,4-diradical intermkdiaire dans cette rkaction contient un dCrivt d'un radical hex-1-knyle; on n'a pas observt la formation de produits provenant de la cyclisation de cet intermediaire en un radical cyclopentylmtthyle. Avec le vinylcyclopropane, quelques produits isolks provenaient aussi d'une photocycloaddition 2 + 2; de plus, on a obtenu des quantitks comparables de produits provenant d'une transposition du 1,4-biradical intermediaire. Dans ce cas, I'intermCdiaire 1,4-biradical qui se forme initialement contient un radical cyclopropylmCthyle qui se transpose en un radical homoallylique; les produits isolCs proviennent d'une disproportionation intramolCculaire en un nouveau 1,7-biradical qui contient le radical homoallylique. La constante de vitesse pour la transposition du radical cyclopropylmCthyle en radical homoallylique est connue et on l'a utilisCe comme horloge pour Cvaluer le temps de vie du 1,4-biradical produit initialeme...

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Radical clocks as probes of 1,4-biradical intermediates in the photochemical cycloaddition reactions of 2-cyclopentenone with alkenes

Rudolph¹,

Weedon²

1990

Can. J. Chem.

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“…Coupling of the radicals with 1,1,3,3-tetramethylisoindolin-2-yloxyl (4) was used as the competing 4 reaction for clocking abstraction of Br from BrCC1,. Coupling rate constants were estimated from those for diffusion control and the latter were calculated from measured viscosities (10). Coupling with 4 occurred under pseudo first-order conditions, with 4 in about 12-fold excess.…”

Section: Methodsmentioning

confidence: 99%

“…The synthesis and spectra of 1 have been reported (10). Hydroxydiazenes 2 and 3 were prepared by analogous procedures, from l-butylhydrazine and phenylhydrazine, respectively.…”

Section: Methodsmentioning

confidence: 99%

“…[3], with kc = 0.2kd = 2.11 X lO%-'s-', where kd, the diffusion controlled rate constant, was calculated from the 15 viscosity of BrCCI, at 80°C (0.735 cP) as described earlier (10). The viscosity was not corrected for the presence of 4 2 , and the products of attack on the cis double bond) and 6-bromo-5-trichloromethyldecomposition of 2.…”

Section: Rate Corlstarltsmentioning

confidence: 99%

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Rate constants for abstraction of bromine from bromotrichloromethane by butyl, cyclopropylmethyl, and phenyl radicals in solution

Mathew¹,

Warkentin²

1988

Can. J. Chem.

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LUKOSE MATHEW and JOHN WARKENTIN. Can. J. Chem. 66, l l (1988).The radical chain decomposition of cyclopropylmethyl (I-hydroxy-1-mcthylethy1)-diazcnc ((CH3)2C(OH)N=NCHI--<1 1) at 253-341 K in hexafluorobenzene or in dichloromethane solution containing brornotrichloromethane affords cyclopropylmethyl bromide, 4-bromo-I-butene, I-bromo-5,5,5-trichloro-2-pentene, and 3,5-dibromo-I, I, I-trichloropcntane from the cyclopropylmethyl portion of 1. Other major products are nitrogen, acetone, and chloroform. The rate constant for formation of cyclopropylmethyl bromide by attack of cyclopropylmethyl free radicals from 1 at bromine of BrCCI, (kyy) was calculated from the product composition using the known rate constant for rearrangement of cyclopropylmethyl radicals to 3-buten-I-yl radicals. At 25"C, kTF = 6.5 X lo8 M-I s-I and the temperature dependence is given by log (ksm/M-I s-) = ( 10.6 5 0.3) -(2.4 C 0.4)/0, where 0 = 2.3R~kcal/mol-l. Non-chain decompositionof (CH3),C(OH)N=N-R(2, R = Bu, and3, R = Ph) in the presence of excess 1 ,I ,3,3-tetramethylisoindolin-2-yloxyl (4) and bromotrichloromethane afforded BuBr and PhBr, respectively, in yields determined by the relative concentrations of 4 and BrCCI3. Rate constants for coupling ( k c ) of Bu. and Ph. with 4 were assumed to be proportional to rate constants for diffusion controlled reactions, kd, which were estimated from measured viscosities. Values of k ! : and k; : , calculated from kc and product yields for reactions at 80°C, are 0.26 X lo9 and 1.55 X lo9 M-' s-l, respectively. The relative radical reactivities toward BrCC13 at 80°C are Ph, 6; cpm, 5; Bu, 1.LUKOSE MATHEW et JOHN WARKENTIN. Can. J. Chem. 66, 1 1 (1988).La dCcomposition radicalaire en chaine du cyclopropylmCthy1 (hydroxy-l methyl-1 Cthyl) diazkne ((CH3)2C(OH)N= NCH2CH(CH2),, I), a des tempkratures allant de 253 2 341 K, dans des solutions d'hexafluorobenzkne ou de dichloromCthane contenant du bromotrichloromtthane, conduit au bromure de cyclopropylmCthyle, au bromo-4 butkne-I, au bromo-l trichloro-5,5,5 pentkne-2 et au dibromo-3,5 trichloro-l ,I , l pentane qui dtrivent tous de la portion cyclopropylmCthyle du compost 1. Les autres produits importants sont l'azote, I'acCtone et le chloroforme. On a calculi2 la constante de vitesse pour la formation du bromure de cyclopropylmtthyle par attaque des radicaux libres cyclopropylmCthyles, provenant du compost 1, au niveau du brome du BrCC13 (kTF); pour ce faire, on afait appel a lacomposition des produits-et on a utilisC la constante de vitesse connue pour la transposition des radicaux cyclopropylmCthyles en radicaux butkne-3 yles. A 25"C, kgm = 6.5 X lo8 M-' s-I et lavariation avec la tempkratureest donnte parl'iquation suivante : log (kxm/M-I s-I) = (10,6 C 0,3) -(2,4 -C 0,4)/0, dans laquelle 0 = 2,3R~kcal/rnol-'. Les dCcompositions des composCs (CH3)?C(OH)N=N-R (2, R = Bu, et 3, R = Ph) par un processus qui n'implique pas de chaines, en presence d'un excks de tCtramCthyl-1,1,3,3 isoindolinyl-2 oxyl (4) et de bromotrichloromCthane, fournissent respect...

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The Saegusa Oxidation and Related Procedures

Bras

Мuzart

2019

Organic Reactions

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The cyclopropylmethyl free-radical clock. Calibration for the 30-89.degree. C range

Cited by 75 publications

References 0 publications

Radical clocks as probes of 1,4-biradical intermediates in the photochemical cycloaddition reactions of 2-cyclopentenone with alkenes

Radical clocks as probes of 1,4-biradical intermediates in the photochemical cycloaddition reactions of 2-cyclopentenone with alkenes

Rate constants for abstraction of bromine from bromotrichloromethane by butyl, cyclopropylmethyl, and phenyl radicals in solution

The Saegusa Oxidation and Related Procedures

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