Photoisomerization of Dialkylbenzenes

Wilzbach, K. E.; Kaplan, Louis

doi:10.1021/ja01065a056

Cited by 68 publications

(43 citation statements)

References 1 publication

(1 reference statement)

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“…For example, the reaction LiH+ D 2 → LiD+ HD has a low energy barrier ͑6.9 kcal/mol DFT͒, and is the basis for a process to create isotopically labeled lithium hydride. 43 eFF correctly reproduces the trapezoidal geometry of the transition state, as well as the linear geometry of the precomplex intermediate ͑Fig. 12͒.…”

Section: G Reactions Involving Hydrogen; Allowed Versus Forbidden Rementioning

confidence: 75%

The dynamics of highly excited electronic systems: Applications of the electron force field

Goddard

2009

The Journal of Chemical Physics

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Highly excited heterogeneous complex materials are essential elements of important processes, ranging from inertial confinement fusion to semiconductor device fabrication. Understanding the dynamics of these systems has been challenging because of the difficulty in extracting mechanistic information from either experiment or theory. We describe here the electron force field ͑eFF͒ approximation to quantum mechanics which provides a practical approach to simulating the dynamics of such systems. eFF includes all the normal electrostatic interactions between electrons and nuclei and the normal quantum mechanical description of kinetic energy for the electrons, but contains two severe approximations: first, the individual electrons are represented as floating Gaussian wave packets whose position and size respond instantaneously to various forces during the dynamics; and second, these wave packets are combined into a many-body wave function as a Hartree product without explicit antisymmetrization. The Pauli principle is accounted for by adding an extra spin-dependent term to the Hamiltonian. These approximations are a logical extension of existing approaches to simulate the dynamics of fermions, which we review. In this paper, we discuss the details of the equations of motion and potentials that form eFF, and evaluate the ability of eFF to describe ground-state systems containing covalent, ionic, multicenter, and/or metallic bonds. We also summarize two eFF calculations previously reported on electronically excited systems: ͑1͒ the thermodynamics of hydrogen compressed up to ten times liquid density and heated up to 200 000 K; and ͑2͒ the dynamics of Auger fragmentation in a diamond nanoparticle, where hundreds of electron volts of excitation energy are dissipated over tens of femtoseconds. These cases represent the first steps toward using eFF to model highly excited electronic processes in complex materials.

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Section: G Reactions Involving Hydrogen; Allowed Versus Forbidden Rementioning

confidence: 75%

The dynamics of highly excited electronic systems: Applications of the electron force field

Goddard

2009

The Journal of Chemical Physics

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“…The phototransposition reactions of 10 have been described in the early literature (1,18) and have been repeated in AN by Pincock and co-workers more recently (13). The ratio of meta to para isomers is 11:1 (obtained at very low conversion), indicating that both one-step and two-step phototranspositions are occuring in the primary photochemical event.…”

Section: Setmentioning

confidence: 85%

“…[1]) and by Burgsthaler et al (2) for di-tert-butylbenzenes. It was demonstrated (3), by photolysis of [1,3,5-14 C 3 ]-mesitylene (eq.…”

Section: Introductionmentioning

confidence: 94%

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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“…M is any molecule which can act as a vibrational quencher, while N is total FB and BiA. In this mechanism, some steps such as intramolecular rearrangement of either singlet or triplet FB, which are known to occur (18)(19)(20) for benzene and substituted benzenes, have been omitted since these steps have very small quantum yields (21). Application of the steady-state treatment to the mechanism yields Can.…”

Section: Resultsmentioning

confidence: 99%

“…3 and 4). Equation [17] also allows the evaluation of kg/klO at various wavelengths [18] intercept/slope = kg/kl0 [B] Values of these ratios are listed below Our data indicate, then, FB intersystem crossover from the first singlet to the triplet may occur from a variety of vibrational levels, depending on the wavelengths of the incident radiation. Consequently, the triplet BiA molecules, produced by energy transfer between triplet FB and ground state BiA, will have a range of vibrational energies also dependent on the excitation wavelength.…”

Section: Resultsmentioning

confidence: 99%

Spectrofluorometric studies. VIII. The effect of CO₂ and CHCl₃ on the photochemistry of monofluorobenzene

Macbeath¹,

Unger²

1970

Can. J. Chem.

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The sensitized emission of biacetyl technique was used to study the effect of CHCI, and CO, on the triplet quantum yields of both benzene and monofluorobenzene.The rnonofluorobenzene was studied at h excitation (h,,) of 2470, 2590, and 2670 A. At 2470 A, the triplet yield increased by over 40% with both added gases; at h,, 2590 A, by around 30%; and at h,, 2670 A, about 20%. CHCI, is slightly more effective than CO, in enhancing the biacetyl phosphorescent yield. The quantum yield of fluorescence was unchanged with these added gases. Using a slightly improved technique, the comparison irradiation of a benzene-biacetyl mixture at h,, 2540 A with added CHCI, was repeated. The results confirmed that the biacetyl phosphorescent yield decreased with increasing pressures of CHCI,, but suggest that the effect is not as great as previously reported. At the same wavelength, the triplet yield is unaffected by the addition of CO,. The quantum yield of fluorescence of benzene is virtually unaffected by the added gases. The data suggest that in the monofluorobenzene case the CO, and CHCI, are quenching vibrationally excited triplet fluorobenzene molecules.

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Photoisomerization of Dialkylbenzenes

Cited by 68 publications

References 1 publication

The dynamics of highly excited electronic systems: Applications of the electron force field

The dynamics of highly excited electronic systems: Applications of the electron force field

Steric effects in the phototransposition reactions of dialkylbenzenes

Spectrofluorometric studies. VIII. The effect of CO₂ and CHCl₃ on the photochemistry of monofluorobenzene

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Photoisomerization of Dialkylbenzenes

Cited by 68 publications

References 1 publication

The dynamics of highly excited electronic systems: Applications of the electron force field

The dynamics of highly excited electronic systems: Applications of the electron force field

Steric effects in the phototransposition reactions of dialkylbenzenes

Spectrofluorometric studies. VIII. The effect of CO2 and CHCl3 on the photochemistry of monofluorobenzene

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Spectrofluorometric studies. VIII. The effect of CO₂ and CHCl₃ on the photochemistry of monofluorobenzene