Structural Effects in the Photochemical Processes of Ketones in Solution

Pitts, James N.; Johnson, Harry W.; Kuwana, Theodore

doi:10.1021/j100818a033

Cited by 106 publications

(34 citation statements)

References 4 publications

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“…With the assumption that the same triplet is responsible for hydrogen abstraction (k,), and that the triplet reacts only with the olefin the following SternVolmer relationship may be derived For purposes of comparison with cyclopentenone the quenching of benzophenone triplets in isopropanol by cyclohexenone was investigated. A linear Stern-Volmer plot (31)(32)(33)(34)(35) was obtained with a slope of 105 M -I (Fig. 3).…”

Section: Decay and Reaction Rate Constantsmentioning

confidence: 96%

Photochemical synthesis 29. Photoannelation and cyclohexenone

Mayo¹,

Nicholson²,

Tchir³

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.

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Section: Decay and Reaction Rate Constantsmentioning

confidence: 96%

Photochemical synthesis 29. Photoannelation and cyclohexenone

Mayo¹,

Nicholson²,

Tchir³

1970

Can. J. Chem.

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“…Since an n,a* triplet state is more electrophilic than a r,a* triplet, the compounds that are most efficient in abstracting hydrogen atoms and/or electrons will have a lowest triplet state with predominantly n,a* character (13,14,30,34,45,46). The intrinsic reactivity of the a,a* triplet state toward concerted hydrogen abstraction is 2 to 4 orders of magnitude less than the n,a* triplet (45).…”

Section: Photoreduction Of Quinones Quinone Photochemistrymentioning

confidence: 99%

“…Electron-donating groups destabilize the n,a* triplet state while stabilizing the a,a* triplet state (13)(14)(15)34). For example, the lowest triplet state of 1,4-benzoquinone (T, n,s*) increases in a,a* character as methyl groups are added.…”

Section: Photoreduction Of Quinones Quinone Photochemistrymentioning

confidence: 99%

Photoreduction fluorescence detection of quinones in high-performance liquid chromatography

Poulsen¹,

Birks²

1989

Anal. Chem.

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A slmple, reagent-free photochemlcai reactlon detector for quinones Including, but not ilmited to, the K vitamins is presented. Quinones are photoreduced to dihydroqulnones vla hydrogen abstraction from the hlgh-performance liquid chromatography (HPLC) moblie phase in a postcolumn photoreactor. An advantage over previous reaction-detection methods for quinones Is the slmpiiclty of thls system. No postcolumn reagent addttlon pumps are required. Additionally, the reaction Is accompilshed In a very short reactor which mlnhnlres band broadening and anatysis time. Detectlon Ihnits for many qukrone derlvatlves are In the low -ram range with good selectlvlty. I n this paper, the photochemistry of the detection scheme and its optimization for use in HPLC are discussed. As a sample appllcatlon, the detection of vitamin K, in a plant extract (Capsella bursa pasfw/us) without prefractlonatlon Is Included. A new photoreactor housing for carrying out anaeroblc reactions In low-dlsperslon, PTFE photoreactors is described.

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“…The observation of the E spectrum suggests the participation of TM in the process of radical generation and it could be considered that the radical was generated by It is known that the first excited state of benzophenone is an n,~* triplet (E S : 76; E T = 69 kcal mol-1), and the quantumyield for ISC is 1.0. The ISC proceeds in highly spin specific manner, while the half-life of the triplet state is very short (Tp < 80 ms at 77K) [48]. Figure 5c shows the transient ESR spectrum of 15 generated from the dimer in the presence of 0.2 M benzophenone observed I us after the laser pulse irradiation.…”

Section: Cidep Studies On the Photochemi Cal Cleavage Of Pyridinymentioning

confidence: 99%

Kinetic ESR and CIDEP studies on the monomer-dimer equilibrium systems of pyridinyl radicals

Ikegami

1986

Reviews of Chemical Intermediates

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Structural Effects in the Photochemical Processes of Ketones in Solution

Cited by 106 publications

References 4 publications

Photochemical synthesis 29. Photoannelation and cyclohexenone

Photochemical synthesis 29. Photoannelation and cyclohexenone

Photoreduction fluorescence detection of quinones in high-performance liquid chromatography

Kinetic ESR and CIDEP studies on the monomer-dimer equilibrium systems of pyridinyl radicals

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