Photocycloaddition of 9,10-Dichloroanthracene to 2,5-Dimethyl-2,4-hexadiene. The Singlet Pathway for [4 + 2]-Adduct Formation in Benzene

Saltiel, Jack; Dabestani, Reza; Sears, Donald F.; McGowan, William M.; Hilinski, Ε. F.

doi:10.1021/ja00141a003

Cited by 10 publications

(6 citation statements)

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“…Products have been characterized, and the formation of strained trans -diene adducts taken to indicate that the reaction is concerted. 17a,f (The product structure reflects the dominant ground state conformer of the diene, ,11c not the most stable product). The nature of any intermediates such as excimers is unclear,14f as product formation might account for deactivation 18a the prototype for photochromic systems 2a…”

Section: Introductionmentioning

confidence: 99%

Modeling Photochemical [4 + 4] Cycloadditions: Conical Intersections Located with CASSCF for Butadiene + Butadiene

et al. 1997

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The [4 + 4] photocycloaddition of butadiene + butadiene has been studied at the CASSCF /4-31G level, as a prototype for a class of photochromic systems. For this model system, minima and transition structures are characterized by analytic frequency calculations, and conical intersections are located. Our results indicate that the standard model for the [4 + 4] addition (based on H4) needs to be revised. The reorganization of all 8π electrons is crucial (i.e., it is not always the same 4π electrons that are important). Efficient nonradiative decay of butadiene + butadiene can be explained by the presence of two distinct S 1/S 0 conical intersections. The first-the lowest-energy point on S 1 overall-is preceded by a barrier for the formation of a new σ bond. The resulting structure is similar to those previously characterized for methyl migration in but-1-ene and the addition of ethylene to benzene. A higher-energy barrier leads to a second crossing which resembles the rhomboidal funnel for the [2 + 2] addition of ethylene + ethylene, but which involves only one double bond from each butadiene. Both reaction paths commence at a true pericyclic minimum, at which the (S 0−S 1) energy gap of ∼37 kcal mol-1 prohibits decay.

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Section: Introductionmentioning

confidence: 99%

Modeling Photochemical [4 + 4] Cycloadditions: Conical Intersections Located with CASSCF for Butadiene + Butadiene

et al. 1997

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“…Although we have proposed competing generation of DBA• -and NR• from (DBA-DMHD)* following the mechanisms for a [4+2] adduct formation reported by Saltiel et al [20], no definitive information reflecting generation of NR' from (DBA-DMHD)* is presently obtained. Hence, an alternative mechanism is that NR• is generated by a diffusion-controlled reaction of DBA* with DMHD (cf.…”

Section: Resultsmentioning

confidence: 75%

“…Saltiel et al [20] proposed that an exciplex formed between the lowest excited singlet state (DCA*) of DCA and ground-state DMHD in benzene generated a neutral radical species essentially identical with NR') which was the precursor for formation of a [4+2] adduct. If this is true, the results obtained so far may be summarized as follows (cf.…”

Section: Resultsmentioning

confidence: 99%

Solvent-Dependent Quenching of the Lowest Excited Singlet State of 9,10-Dibromoanthracene by Ground-State 2,5-Dimethylhexa-2,4-Diene Yielding 9-Bromoanthracene or the [4+2] Adduct

1998

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Irrespective of the dielectric constant (ε) or the hydrogen-bonding ability of a pure solvent, the lowest excited singlet state (DBA*) of 9,10-dibromoanthracene (DBA) is quenched by ground-state 2,5-dimethylhexa-2,4-diene (DMHD) giving rise to the appearance of an exciplex emission. By means of sub-picosecond and nanosecond laser photolysis as well as steady-state photolysis, however, the following solvent-dependent results are obtained; (1) in acetonitrile (ε = 37.5) and acetone (ε = 20.7), an exciplex (DBA-DMHD)* formed between DBA* and DMHD generates the DBA radical anion (DBA' -) as an intermediate for formation of 9-bromoanthracene (BA) from DBA; (2) in ethanol (ε = 24.6), 2-propanol (ε = 19.9), 1-octanol (ε = 10.3), diethyl ether (ε = 4.34), and heptane (ε = 1.92)" a neutral radical species (NR') generated by decomposition of (DBA-DMHD)* (or by a reaction of DBA* with DMHD) is an intermediate for formation of a dibenzobicyclo[2.2.2]octadiene-type compound (a [4+2] adduct); (3) both DBA'-and NR' are generated in methanol (ε = 32.7) but the rate (v) of BA formation upon steady-state photolysis of DBA in the presence of 1 M DMHD decreases in the order of v(acetonitrile, ε = 37.5) > v(acetone, ε = 20.7) > methanol, ε = 32.7). It thus can be concluded that the mechanism of exciplex decomposition and the reaction of DBA* with DMHD are affected by not only the dielectric constant of a pure solvent but also its hydrogen -bonding ability.

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“…We have developed , an approach for combining quantum chemistry with dynamics where the gradients that are used to drive the dynamics simulation are evaluated “on the fly” using a hybrid molecular mechanics valence bond (MMVB) method. Our purpose in this paper is to show how such a method can be used to model the photoproduct distribution for a photochemical reaction with two competing excited-state branchesthe [4 + 4] photocycloaddition of butadiene + butadiene 4,5 which is a model for diene + aromatic photoadditions in general. − The major product predicted for butadiene + butadiene by MMVB dynamics is consistent with the limited experimental data available 5c…”

Section: Introductionmentioning

confidence: 58%

“…As well as accounting for the formation of several products, decay funnels such as C and E can explain two other features of diene + aromatic photoadditions in general, e.g. butadiene + benzene, naphthalene, and anthracene. − First, dienes have been found to quench the fluorescence of aromatic molecules, implying a rapid and efficient route to S 0 such as a surface crossing. Second, there is evidence that these reactions are “concerted”: 10a,f if the dominant ground-state conformer of a diene is trans, , then a strained trans addition product is formed, suggesting that there is no intermediate at which rearrangement could take place to form the cis product, which is thermodynamically more stable.…”

Section: Introductionmentioning

confidence: 99%

Product Distributions from Molecular Mechanics−Valence Bond Dynamics: Modeling Photochemical [4 + 4] Cycloadditions

et al. 1998

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The purpose of this paper is to study the model [4 + 4] photocycloaddition of butadiene + butadiene by using direct dynamics calculationswith no geometric constraintsto describe motion along excited-state reaction paths and subsequent decay to the ground state. We use the molecular mechanics−valence bond (MMVB) potential, which is calibrated against previous CASSCF calculations for this system (Bearpark, M. J.; Deumal, M.; Robb, M. A.; Vreven, T.; Yamamoto, N.; Olivucci, M.; Bernardi, F. J. Am. Chem. Soc. 1997, 119, 709−718). Our dynamics calculations show that efficient nonradiative decay of butadiene + butadiene in the presence of two different S 1/S 0 conical intersections can account for the formation of many products. The major product predicted by MMVB is consistent with the limited experimental data available.

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Photocycloaddition of 9,10-Dichloroanthracene to 2,5-Dimethyl-2,4-hexadiene. The Singlet Pathway for [4 + 2]-Adduct Formation in Benzene

Cited by 10 publications

References 0 publications

Modeling Photochemical [4 + 4] Cycloadditions: Conical Intersections Located with CASSCF for Butadiene + Butadiene

Modeling Photochemical [4 + 4] Cycloadditions: Conical Intersections Located with CASSCF for Butadiene + Butadiene

Solvent-Dependent Quenching of the Lowest Excited Singlet State of 9,10-Dibromoanthracene by Ground-State 2,5-Dimethylhexa-2,4-Diene Yielding 9-Bromoanthracene or the [4+2] Adduct

Product Distributions from Molecular Mechanics−Valence Bond Dynamics: Modeling Photochemical [4 + 4] Cycloadditions

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