Laser flash photolysis of 3-phenylcyclopent-2-enone: absorption spectrum and reactivity of its triplet excited state

Kelly, John M.; McMurry, T. Brian H.; Work, D. Neil

doi:10.1039/c39870000280

Cited by 5 publications

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“…We chose to study phenyl substituted enones because of both an increased optical density at the excitation wavelength and an increased lifetime relative to their unsubstituted analogs. [16][17][18] We performed geometry optimizations and frequency calculations at the B3LYP/6-31G* level of theory on both the ground and lowest triplet excited states of each enone. 19 The results of the frequency calculations (scaled by 0.96 20 ) are displayed as bars in Fig.…”

Section: Resultsmentioning

confidence: 99%

Time-resolved IR studies of cyclic enone triplet excited states and their reactions with alkenes

Cohen

Showalter

Brady

et al. 2003

Phys. Chem. Chem. Phys.

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The pp* triplet excited states of 3-phenyl-2-cyclohexenone (1) and 3-phenyl-2-cyclopentenone (2) have been observed by time-resolved infrared (TRIR) spectroscopy. The reaction of various alkenes with the triplet excited state of 2 has also been studied by TRIR spectroscopy, and the partitioning between fragmentation and ring closure of the biradical intermediates involved has been estimated. Within a series of structurally related biradicals, more stable ones undergo ring closure more efficiently. Scheme 1 Representative enone-alkene [2 + 2] reactions. y Dedicated to Professor Dr Z. R. Grabowski and Professor Dr J. Wirz on the occasions of their 75th and 60th birthdays. z Electronic supplementary information (ESI) available: Optimized geometries and ab initio-calculated IR frequencies and intensities for cyclic enones. See

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Section: Resultsmentioning

confidence: 99%

Time-resolved IR studies of cyclic enone triplet excited states and their reactions with alkenes

Cohen

Showalter

Brady

et al. 2003

Phys. Chem. Chem. Phys.

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“…They simply establish that if involved, it is not directly detectable by this technique. Kelly et al (18) recently reported that self-quenching plays a role in the decay of triplet 3-phenylcyclopent-2-enone which has a triplet lifetime of 2.9 IJ.S at room temperature. In the case of ketones 1-111 their triplet lifetimes are much shorter and as a result self-quenching is unlikely to be of importance.…”

Section: Discussionmentioning

confidence: 99%

A reinvestigation of the interaction between triplet states of cyclohexenones and amines

Weir¹,

Scaiano²,

Schuster³

1988

Can. J. Chem.

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. J. Chem. 66, 2595Chem. 66, (1988.Laser flash photolysis studies lead to the conclusion that the short-lived triplet states of cyclohexenones are readily quenched by amines. For example, in the case of 2-cyclohexen-1-one (I) its triplet state (TT = 40 ns in acetonitrile) is quenched by triethylamine with a rate constant of (9.0 2 0.8) x lo7 M-' s-I. Cyclohexenone triplets are also quenched efficiently by DABCO and by triphenylamine leading to the formation of the corresponding amine radical cations. The new evidence reported rules out the involvement of long-lived detectable exciplexes. Cohen and Peters and their co-workers have studied this process with benzophenone and related ketones, and have demonstrated convincingly that the quenching process involves electron transfer to give initially amine radical cations and ketone radical anions (2). Schuster and Brisimitzakis demonstrated that reactive 2,5-cyclohexadienone triplets are quenched by amines of appropriate ionization potential to give a set of products not observed in the absence of amines. In all cases, the amine interacts directly with ketone triplet (3).Reactions of photoexcited a,~-unsaturated carbonyl compounds with amines are known to give 1:l adducts, presumably via the enone triplet states (4). Dunn et al. have reported results of nanosecond flash studies on excitation of cvclohexanone I and analogues such as I1 (see Chart I) in the presence of 1,4-diazabicyclo [2.2.2]octane (DABCO) which demonstrate that long-lived DABCO radical cations (X,,, 450 nm) are formed from an intermediate which has the same lifetime (ca. 25 ns) as the transient species (X,,, 280 nm) generated on laser excitation of the enone in the absence of amines (5). This transient has been suggested by Bonneau (6) and by Schuster et al. (7) to be a highly twisted triplet excited state of these cyclohexenones. In the presence of even small amounts of DABCO, long-lived absorption is observed which interferes with analysis of the fast component of the decay curve at wavelengths in the range 270-300 nm; at the DABCO concentrations required for observation of the growth of the radical cation at 450 nm, the fast decay at 280 nm cannot be monitored (5,8).In contrast to the above findings, Pienta and McKimmey reported results of product analyses from excitation of I in the

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“…4) which is red shifted 12 nm from that of the 3-phenylcyclopentenone triplet absorption spectrum. 18 It is clearly a product of the quenching reaction, probably retains triplet multiplicity and decays unimolecularly. We assume this transient to be either exciplex or triplet 1,4-biradicals arising from the phenylenone and 1-phenylpropene.…”

Section: Cyclohexane Solutionmentioning

confidence: 99%

Photochemistry of substituted cyclic enones. Part 12.1 Photocycloaddition of 3-phenylcyclopentenone and 3-phenylcyclohexenone to (E )- and (Z )-1-phenylpropene

Kelly¹,

Kelly²,

McMurry³

1999

J. Chem. Soc., Perkin Trans. 2

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The quantum yields of adduct formation and isomerisation of (E)-and (Z)-1-phenylpropene by 3-phenylcyclopentenone 1 and 3-phenylcyclohexenone 2 have been measured by 1 H-NMR spectroscopy in solutions of d 6 -benzene. The adducts formed for each photoreaction have been shown to be independent of the starting 1-phenylpropene isomer. For 3-phenylcyclopentenone 1, a photostationary state of 32 : 68 (E)-to (Z)-1-phenylpropene is achieved during the course of the reaction. This isomerisation reaction may occur through reversion of triplet 1,4-biradical intermediates to ground state molecules or by an energy transfer process. However for 3-phenylcyclohexenone 2 isomerisation occurs only through reversion of triplet 1,4-biradical intermediates. The mechanism of photoadduct formation and that of the isomerisation reaction are discussed for both phenylenones.Rate constants for quenching of the 3-phenylcyclopentenone 1 and 3-phenylcyclohexenone 2 triplet states by (E)-and (Z)-1-phenylpropene, 3 and 4, in cyclohexane and benzene solutions have been recorded using laser flash photolysis. In cyclohexane at high quencher concentration, complex decay kinetics are observed consistent with observation of both the enone triplet state and either a triplet exciplex or 1,4-biradical intermediates.

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Laser flash photolysis of 3-phenylcyclopent-2-enone: absorption spectrum and reactivity of its triplet excited state

Cited by 5 publications

References 0 publications

Time-resolved IR studies of cyclic enone triplet excited states and their reactions with alkenes

Time-resolved IR studies of cyclic enone triplet excited states and their reactions with alkenes

A reinvestigation of the interaction between triplet states of cyclohexenones and amines

Photochemistry of substituted cyclic enones. Part 12.1 Photocycloaddition of 3-phenylcyclopentenone and 3-phenylcyclohexenone to (E )- and (Z )-1-phenylpropene

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