J. Am. Chem. Soc.

1968

DOI: 10.1021/ja01016a026

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Mechanistic organic photochemistry. XXXI. Electronic details of the photochemical phenyl migration in 4,4-diphenylcyclohexenone

Howard E. Zimmerman¹,

Kenneth G. Hancock²

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Exploratory Direct Photolysis Of 3-methyl-3-(9-phet~a1zthr~~1

Energy Of the Cyclohexenone Triplet1

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Cited by 41 publications

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“…This seems valid, since the triplet energy of biacetyl T,(BI) is 56 kcal/mol compared with 66.5 kcal/mol observed for T , of the phenanthryl vinyl methane 1. It has been noted (9) that triplet transfer processes which are 10 kcal/mol or more exothermic usually are diffusion controlled. Additionally, a bimolecular rate of diffusion of 2.3 X 10" s-' was calculated from the modified Debye equation (lo This led to 0.17 milliseconds for the lifetime (7) of the phenanthryl vinyl methane triplet '1.…”

Section: Methodsmentioning

confidence: 99%

“…Solvent removal in vacuo left 141 mg of material which was chromatographed on a 1.5 cm x 75 cm silica gel column. Elution with hexane and then 1% ether with 50 mL fractions gave 62 mg (4 1 %) of starting material in fractions 4-7 and 33 mg (22%) of product in fractions [8][9][10][11][12][13]. Stripping the column with 5% ether afforded 25 mg of unidentified ' The starting material was identified by nmr comparison with an authentic sample and the product was recrystallized to mp 39-40°C and proved to be identical with synthetically preparcd 2-methyl-4 -(9-phenanthry1)-l -butene.…”

Section: Exploratory Direct Photolysis Of 3-methyl-3-(9-phet~a1zthr~~mentioning

confidence: 99%

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The photochemistry of phenanthrene-substituted molecules

Wu²

1983

Can. J. Chem.

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7'11i.y 1)[1per is cledicoted to PI-ofessor Harry E. G L~I I~I~I~S 0 1 1 file occcr.sio11 of his 65th birtt~rlrlyHOWARD E. ZIMMERMAN and GUO-SHENG WU. Can. J. Chcm. 61, 866 (1983).The photochemistry of 3-methyl-3-(9-phcnanthry1)-1-butene was examined as part of 'an investigation into the effects of having two n chromophores of widely different energies participating in a di-n-methane rearrangement. Wc observed both direct and sensitized reactivity with quantum yiclds = 0.043 and 0.053. Thc primary reaction product from both direct and sensitized photolyses was I, 1-dimethyl-2-(9-phenanthryl)cyclopropan. However, in practice this product was obtained only from sensitized irradiations where it was almost completely unreactive. The triplet reactivity is unusual in that the typical free rotor decay exhibited by triplets does not lead to inhibition of di-n-methane reactivity in this case. This point is discussed. The intersystcm crossing efficiency of the phcnanthryl vinyl mcthanc reactant was obtained from the scnsitization of biacetyl phosphorescence by the phenanthrene derivative at varying biacetyl concentrations. This was +, , , = 0.86. This result and the bracketing relationships signify that essentially all of the direct irradiation rearrangement utilizes T I . In addition, from these experiments, 'k,,,,,,, was determined as 5.8 X 10' s-I. Similarly, 'k, = 250 s-I which is the slowest di-n-methane rearrangement encountered thus far. The rearrangement of the cyclopropane product to form 2-methyl-4-(9-phenanthry1)-I-butene was also investigated. 'I$ was determined to be 0.091 and '41 was determined as 0.00072. Thus the interesting contrast was encountered in which thc di-n-methane rearrangement proceeds from the triplet while the rearrangement of the cyclopropane product proceeds most efficiently from the singlet. HOWARD E. ZIMMERMAN et GUO-SHENG WU. Can. J. Chcm. 61, 866 (1983).On a CtudiC la photochimie du mCthyl-3-(phenanthryl-9-)-3 butene-I comme un aspcct dc la rechcrchc portant sur les effets de la presence de dcux chromophores n d'inergies tres differentes participant h la transposition di-n-mkthane. Nous avons observC les deux rCactivitCs directe et scnsibilisCc avec des rendemcnts quantiqucs +"IK = 0,043 et +SEN" 0,535. Le dimethyl-1, l (phinanthryl-9)-2 cyclopropane et le produit primaire de rCaction h partir de la photolyse directe et de la photolyse sensibiliske. Cependant, en fait, on obtient ce produit uniquement h partir des irradiations faites en presence de photosensibilisateurs oh il est presque complktement inactif. La reactivitk du triplet est inhabituelle en ce sens quc la dksintegration par centrifiguration libre typique exhibee par les triplets ne conduit pas h une inhibition de la r6activitC du di-n-methane dans ce cas. On discute de ce point. On retrouve I'efficacitC du croisement intersystkme du rCactif phCnanthrylvinyl methane h partir de la sensibilisation de la phosphorescence du biacCtyle par le derive du phknanthrene h des concentrations variables de biacCtyle. Cette efficacitk est...

“…This seems valid, since the triplet energy of biacetyl T,(BI) is 56 kcal/mol compared with 66.5 kcal/mol observed for T , of the phenanthryl vinyl methane 1. It has been noted (9) that triplet transfer processes which are 10 kcal/mol or more exothermic usually are diffusion controlled. Additionally, a bimolecular rate of diffusion of 2.3 X 10" s-' was calculated from the modified Debye equation (lo This led to 0.17 milliseconds for the lifetime (7) of the phenanthryl vinyl methane triplet '1.…”

Section: Methodsmentioning

confidence: 99%

“…Solvent removal in vacuo left 141 mg of material which was chromatographed on a 1.5 cm x 75 cm silica gel column. Elution with hexane and then 1% ether with 50 mL fractions gave 62 mg (4 1 %) of starting material in fractions 4-7 and 33 mg (22%) of product in fractions [8][9][10][11][12][13]. Stripping the column with 5% ether afforded 25 mg of unidentified ' The starting material was identified by nmr comparison with an authentic sample and the product was recrystallized to mp 39-40°C and proved to be identical with synthetically preparcd 2-methyl-4 -(9-phenanthry1)-l -butene.…”

Section: Exploratory Direct Photolysis Of 3-methyl-3-(9-phet~a1zthr~~mentioning

confidence: 99%

The photochemistry of phenanthrene-substituted molecules

Wu²

1983

Can. J. Chem.

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7'11i.y 1)[1per is cledicoted to PI-ofessor Harry E. G L~I I~I~I~S 0 1 1 file occcr.sio11 of his 65th birtt~rlrlyHOWARD E. ZIMMERMAN and GUO-SHENG WU. Can. J. Chcm. 61, 866 (1983).The photochemistry of 3-methyl-3-(9-phcnanthry1)-1-butene was examined as part of 'an investigation into the effects of having two n chromophores of widely different energies participating in a di-n-methane rearrangement. Wc observed both direct and sensitized reactivity with quantum yiclds = 0.043 and 0.053. Thc primary reaction product from both direct and sensitized photolyses was I, 1-dimethyl-2-(9-phenanthryl)cyclopropan. However, in practice this product was obtained only from sensitized irradiations where it was almost completely unreactive. The triplet reactivity is unusual in that the typical free rotor decay exhibited by triplets does not lead to inhibition of di-n-methane reactivity in this case. This point is discussed. The intersystcm crossing efficiency of the phcnanthryl vinyl mcthanc reactant was obtained from the scnsitization of biacetyl phosphorescence by the phenanthrene derivative at varying biacetyl concentrations. This was +, , , = 0.86. This result and the bracketing relationships signify that essentially all of the direct irradiation rearrangement utilizes T I . In addition, from these experiments, 'k,,,,,,, was determined as 5.8 X 10' s-I. Similarly, 'k, = 250 s-I which is the slowest di-n-methane rearrangement encountered thus far. The rearrangement of the cyclopropane product to form 2-methyl-4-(9-phenanthry1)-I-butene was also investigated. 'I$ was determined to be 0.091 and '41 was determined as 0.00072. Thus the interesting contrast was encountered in which thc di-n-methane rearrangement proceeds from the triplet while the rearrangement of the cyclopropane product proceeds most efficiently from the singlet. HOWARD E. ZIMMERMAN et GUO-SHENG WU. Can. J. Chcm. 61, 866 (1983).On a CtudiC la photochimie du mCthyl-3-(phenanthryl-9-)-3 butene-I comme un aspcct dc la rechcrchc portant sur les effets de la presence de dcux chromophores n d'inergies tres differentes participant h la transposition di-n-mkthane. Nous avons observC les deux rCactivitCs directe et scnsibilisCc avec des rendemcnts quantiqucs +"IK = 0,043 et +SEN" 0,535. Le dimethyl-1, l (phinanthryl-9)-2 cyclopropane et le produit primaire de rCaction h partir de la photolyse directe et de la photolyse sensibiliske. Cependant, en fait, on obtient ce produit uniquement h partir des irradiations faites en presence de photosensibilisateurs oh il est presque complktement inactif. La reactivitk du triplet est inhabituelle en ce sens quc la dksintegration par centrifiguration libre typique exhibee par les triplets ne conduit pas h une inhibition de la r6activitC du di-n-methane dans ce cas. On discute de ce point. On retrouve I'efficacitC du croisement intersystkme du rCactif phCnanthrylvinyl methane h partir de la sensibilisation de la phosphorescence du biacCtyle par le derive du phknanthrene h des concentrations variables de biacCtyle. Cette efficacitk est...

“…It is noteworthy that Zimmerman and Hancock have observed weak emission in this region from 4,4-diphenylcyclohexenone (27).…”

Section: Energy Of the Cyclohexenone Tripletmentioning

confidence: 83%

Photochemical synthesis 29. Photoannelation and cyclohexenone

Mayo¹,

1970

Can. J. Chem.

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Values of 1.7 x 10' s-I and 2.5 x lo7 M-' s-' for k,, the unimolecular rate constant for decay, and k,, the rate constant for addition to cyclohexene, have been obtained for cyclohexenone. These indicate that this cyclenone decays somewhat faster and reacts significantly slower with the same substrate (in the same solvent) than does cyclopentenone. Evidence is adduced, from sensitization experiments and the phosphorescence quenching of a range of carbonyl compounds, that the reactive triplet and lowest triplet of cyclohexenone lie close together, if they are indeed not identical, and the energy of this triplet is in the region of 66-68 kcal/mole. This is higher than that indicated by photostationary state measurements. This latter method, applied to cyclenones, may be suspect, and triplet energies so derived subject to doubt (that of cyclopentenone included) or have a different significance from those obtained by other methods. Further attempts to demonstrate the existence of a lower, cycloadditively unreactive, triplet in cyclopentenone have been negative. It now seems far more likely that the original interpretation was in error, that the lowest energy triplet is near 73 kcal/mole, and that a special mechanism for quenching benzophenone triplets by ground state cyclopentenone exists. The evidence for other multiple reactive triplets is re-examined as is the evidence for the nature of the states involved.

“…By way of contrast, the cis isomer of enone 3 (i.e., compound 7, eq. [3]), which could be isolated in small amounts when 3 was irradiated for relatively short periods of time (vide infra), exhibited an NMR spectrum in which the vinyl doublets appeared at 6.79 and 6.32 ppm with a mutual coupling constant of 12 Hz. The photochemistry of enone 3 was examined in both benzene and acetontrile solution and the progress of the reaction monitored by gas chromatography.…”

Section: Resultsmentioning

confidence: 99%

The photochemistry of trans-1,4,4,4-tetraphenyl-but-2-en-1-one: A highly efficient aryl migration (type B) enone photorearrangement

2003

Can. J. Chem.

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4,4, in acetonitrile or benzene leads to trans-cis isomerization (7) along with rearrangement to trans-1-benzoyl-2,2,3-triphenylcyclopropane (8). Formation of the latter product represents a new example of the aryl migration (type B) enone photorearrangement reaction first reported by Zimmerman and co-workers for 4,4-diphenylcyclohex-2-en-1-one (1). The quantum yield in the case of enone 3 (0.4) is approximately 10 times greater than that for 4,4,-diphenylcyclohex-2-en-1-one, a result that is ascribed to steric acceleration of phenyl migration from the triphenylmethyl group plus greater resonance stabilization of the intermediate biradical.Résumé : La photolyse de la trans-1,4,4,4-tétraphénylbut-2-én-1-one (3) dans l'acétonitrile ou le benzène conduit à une isomérisation trans-cis (7) ainsi qu'à un réarrangement en trans-1-benzoyl-2,3,3-triphénylcyclopropane (8). La formation de ce dernier produit représente un nouvel exemple de réaction de photoréarrangement d'énone avec migration d'aryle (type B) qui avait été observé pour la première fois par Zimmerman et ses collaborateurs pour la 4,4-diphénylcyclohex-2-én-1-one (1). Le rendement quantique dans le cas de l'énone 3 (0,4) est approximativement dix fois plus grand que celui observé avec la 4,4-diphénylcyclohex-2-én-1-one; on attribue cette différence à l'accélération sté-rique associée à la migration du phényle à partir du groupe triphénylméthyle ainsi qu'à la plus grande stabilisation par résonance du biradical intermédiaire.

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