The organic photochemistry of benzene—II

Bryce‐Smith, D.; Gilbert, Andrew

doi:10.1016/0040-4020(77)80069-0

Cited by 120 publications

(45 citation statements)

References 165 publications

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“…This possibility demonstrates that the measurement of quantum yields of formation of products cannot, in general, give reliable values of k r . [7] k t = k f + k ic + k isc + k r [8] k t = k f + k isc + A exp(-E a /RT) Values for k t as a function of temperature for applying eq. [8] have normally been obtained by measuring S 1 lifetimes (τ s ), but this is a very time-consuming process.…”

Section: Measurement Of Rate Constants Of Reaction Of S 1 By the Tempmentioning

confidence: 99%

“…[7] k t = k f + k ic + k isc + k r [8] k t = k f + k isc + A exp(-E a /RT) Values for k t as a function of temperature for applying eq. [8] have normally been obtained by measuring S 1 lifetimes (τ s ), but this is a very time-consuming process. Nevertheless, we used that method for Sets 2 and 3, and the results are given in Tables S2 and S3.…”

Section: Measurement Of Rate Constants Of Reaction Of S 1 By the Tempmentioning

confidence: 99%

“…[7] and [8], where the total rate constant of decay of the excited singlet state (k t ) is the sum of all the rate constants of the individual processes: fluorescence (k f ), internal conversion (k ic ), intersystem crossing (k isc ), and the reaction itself (k r ). Equation [8] results from the assumptions that nonactivated internal conversion for substituted benzenes is very slow (~10 3 s -1 ) (26), and that k r is the only activated process and follows an Arrhenius expression. From Scheme 2 and Fig.…”

Section: Measurement Of Rate Constants Of Reaction Of S 1 By the Tempmentioning

confidence: 99%

“…[3]) for benzene-d 6 in 2,2,2-trifluoroethanol (TFE) on photolysis in alcohol solvents (5,6). Research in this area up until 1980 has been the subject of several reviews (7)(8)(9)(10).…”

Section: Introductionmentioning

confidence: 99%

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Steric effects in the phototransposition reactions of dialkylbenzenes

Gonzalez¹,

Pincock²

2006

Can. J. Chem.

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The photochemistry, photophysical properties, and temperature dependence (-25 to +65°C) of fluorescence by quantum yields and excited singlet state lifetimes in acetonitrile have been examined for three sets of dialkylbenzene derivatives: Set 1 -ortho-xylene (10), tetralin (11), and indan (12); Set 2 -2,3-dimethylbenzonitrile (9-23), 5-cyanotetralin (T-23), and 4-cyanoindan (I-23); and Set 3 -3,4-dimethylbenzonitrile (9-34), 6-cyanotetralin (T-34), and 5-cyanoindan (I-34). Phototransposition reactions occur for 10, 9-23, 9-34, and T-34. Fitting of the temperature-dependent fluorescence data to an Arrhenius expression gave A and E a values for all substrates studied except I-23 and I-34. The fluorescence intensity of these two compounds was essentially independent of temperature. For the other compounds, the data revealed that the activation barrier separating the excited singlet state (S 1 ) from the reactive intermediate, a prefulvene biradical, was the important one in determining the reaction efficiency. The dominant mode of decay of the reactive intermediate was internal return to the starting material. Moreover, the general observation was made that nitrile substitution ortho to one of the alkyl groups in these dialkylbenzene derivatives reduced the rate at which they were converted to the reactive intermediate and, therefore, also the efficiency of the phototransposition reactions.Résumé : En se basant sur les rendements quantiques ainsi que les temps de vie de l'état singulet excité observés lors de réactions dans l'acétonitrile, on a étudié la photochimie, les propriétés photophysiques et la relation entre la tempé-rature (-25 à +65°C) et les rendements quantiques pour trois ensembles de dérivés benzéniques dialkylés, soit l'ensemble 1 formé d'ortho-xylène (10), de tétraline (11) et d'indane (12); l'ensemble 2 formé de 2,3-diméthylben-zonitrile (9-23), de 5-cyanotétraline (T-23) et de 4-cyanoindane (I-23); l'ensemble 3 formé de 3,4-diméthylbenzonitrile (9-34), de 6-cyanotétraline (T-34) et de 5-cyanoindane (I-34). Il se produit des réactions de phototransposition pour les composés 10, 9-23, 9-34 et T-34. Un ajustement des données de fluorescence influencées par la température à une expression d'Arrhenius permet de calculer les valeurs A et E a pour tous les substrats étudiés, à l'exception de I-23 et I-34. L'intensité de la fluorescence de ces deux composés est essentiellement indépendante de la température. Pour les autres composés, les données ont permis de déterminer que la barrière d'activation qui sépare S 1 , l'état singulet excité, de l'intermédiaire réactif, un biradical préfulvène, est celle qui est importante dans la détermination de l'efficacité de la réaction. Le mode dominant dans la désactivation de l'intermédiaire réactif est le retour interne vers le produit de dé-part. De plus, on a observé que la présence d'un substituant nitrile en position ortho par rapport aux groupes alkyles de ces dialkylbenzènes provoque une réduction de la vitesse avec laquelle ils se transforment en intermédiaire...

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Section: Measurement Of Rate Constants Of Reaction Of S 1 By the Tempmentioning

confidence: 99%

Section: Measurement Of Rate Constants Of Reaction Of S 1 By the Tempmentioning

confidence: 99%

Section: Measurement Of Rate Constants Of Reaction Of S 1 By the Tempmentioning

confidence: 99%

“…[3]) for benzene-d 6 in 2,2,2-trifluoroethanol (TFE) on photolysis in alcohol solvents (5,6). Research in this area up until 1980 has been the subject of several reviews (7)(8)(9)(10).…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Steric effects in the phototransposition reactions of dialkylbenzenes

Gonzalez¹,

Pincock²

2006

Can. J. Chem.

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“…1,2 In the presence of alkenes photocycloaddition can result, leading to ortho, meta, and para adducts, for example, [2+2], [3+2] and [4+2] cycloadditions, Figure 1. meta-Cycloaddition of alkenes with benzene has been extensively exploited to construct a dazzling array of synthetic targets, [3][4][5] while ortho and para cycloadditions of benzene have received less attention.…”

Section: Introductionmentioning

confidence: 99%

Photo-[4+4]-cycloaddition (para) of meta-substituted benzenes with 2-pyridones

Khatri

Vrubliauskas

Sieburth

2015

Tetrahedron Letters

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a b s t r a c tBenzene is unreactive as a photochemistry partner with 2-pyridone, however benzene substitution can allow for an efficient [4+4] (a k a, 'para') photocycloaddition. Productive substituents include alkoxy, cyano, ester, and trifluoromethyl, suggesting that inductively electron-withdrawing groups are sufficient, however a single fluorine substituent does not result in cycloaddition. When the product of this cycloaddition contains a conjugated system (e.g., an unsaturated ester) a secondary photocycloaddition can follow, forming triply bridged all-syn-[3]ladderane products.

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Stereospecific nucleophilic trapping of encounter complexes between photoexcited 1-cyanonaphthalene and norbornadiene

Weng

Roth

1998

J. Phys. Org. Chem.

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Photo-induced electron donor-acceptor reactions between 1-cyanonaphthalene (CNN) and norbornadiene (N) generate products of several structure types. Methanol adducts (1-3) formed in polar solvents are rationalized via the radical cation, N Á , and stereospecific (exo-) nucleophilic attack by methanol. In less polar solvents, CNN and N form [2 + 2]-cycloadducts, exclusively on the exo-face of N. In non-polar solvents containing methanol, CNN, N and methanol combine to form 1:1:1 adducts, containing the sensitizer on the endo-and the methoxy groups on the exo-face. The formation of these products is rationalized via the trapping of encounter complexes of different geometries. Any rearrangement of the norbornenyl system can be eliminated, since neither tricyclyl nor 7-methoxynorbornenyl structures are formed. Apparently, the alcohol captures an endo-encounter complex of CNN and N by attack from the exo-face, similar to the attack of methanol on N Á .

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The organic photochemistry of benzene—II

Cited by 120 publications

References 165 publications

Steric effects in the phototransposition reactions of dialkylbenzenes

Steric effects in the phototransposition reactions of dialkylbenzenes

Photo-[4+4]-cycloaddition (para) of meta-substituted benzenes with 2-pyridones

Stereospecific nucleophilic trapping of encounter complexes between photoexcited 1-cyanonaphthalene and norbornadiene

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