CIDNP study of the photoreduction of benzophenone with secondary alcohols

Hollander, Jan A. den; Hartel, Arnold J.; Schippers, P. H.

doi:10.1016/0040-4020(77)80128-2

Cited by 10 publications

(1 citation statement)

References 33 publications

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“…2b Similar memory effects have been reported previously.' 5, 16 It is well-known that the energy level of NBD' lies significantly below that of QC" (by 9-1 1 kcal rn0l-')~9" and that the excited singlet energy surface connecting NBD and QC delivers singlet excited molecules preferentially to NBD. ' 9 l 8 Therefore, it is expected that the singlet DBMBF, could not sensitize the isomerization of NBD to QC4 even if the free energy difference calculated by the Rehm-Weller equation ' favours the electron transfer and NBD quenches singlet excited DBMBF, with a near diffusion limited rate constant (see Table 2).…”

Section: Discussionmentioning

confidence: 99%

Electron transfer photoisomerization of norbornadiene to quadricyclane cosensitized by dibenzoylmethanatoboron difluoride and aromatic hydrocarbons

Liu¹,

Zhang²,

Li³

et al. 1994

J. Chem. Soc., Perkin Trans. 2

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Chemically induced dynamic nuclear polarization (CI DN P) was used to study the valence isomerization of norbornadiene (N BD) to quadricyclane (QC) sensitized by dibenzoylmethanatoboron difluoride (DBMBF,). While DBMBF, readily sensitized QC to NBD via an electron transfer mechanism, it did not promote the reverse isomerization. In contrast, in the presence of an aromatic co-sensitizer, such as toluene, ethylbenzene, biphenyl or durene, DBMBF, sensitized NBD isomerization to QC. The novel result is rationalized by invoking a photoinduced electron transfer mechanism, involving triplexes as the key intermediate which facilitates triplet recombination of the ion radical pair.The photosensitized valence isomerization of norbornadiene (NBD) to quadricyclane (QC) has been the subject of intense experimental and theoretical investigation in view of its significance in solar energy storage and mechanistic interests. Recently one of us has reported that dibenzoylmethanatoboron difluoride (DBMBF,) sensitized, from its singlet excited state, the photoisomerization of QC to NBD with high efficiency, but did not sensitize the reverse conversion, NBD to QC." It was proposed that the conversion of QC to NBD was initiated by photoinduced electron transfer between DBMBF, and QC, and that the failure of the reverse conversion was due to the unfavourable energetics of the NBD'+ to QC.' tran~formation.~We have probed the intermediate involved in the cation radical reaction of the DBMBF, sensitized NBD-QC valence isomerization by chemically induced dynamic nuclear polarization (CIDNP). In the process, we have found that certain aromatic compounds could also act as co-catalysts, driving DBMBF, sensitizing of NBD isomerization to QC (Scheme l), causing CIDNP effects and NMR line-broadening of DBMBF, c c ' \ /' o. . B.

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Section: Discussionmentioning

confidence: 99%

Electron transfer photoisomerization of norbornadiene to quadricyclane cosensitized by dibenzoylmethanatoboron difluoride and aromatic hydrocarbons

Liu¹,

Zhang²,

Li³

et al. 1994

J. Chem. Soc., Perkin Trans. 2

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Kinetics of Ketyl Radical Reactions Occurring in the Photoreduction of Benzophenone by Isopropyl Alcohol

Demeter

László

Bérces

1988

Ber Bunsenges Phys Chem

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Benzophenone – isopropyl alcohol – acetonitrile, benzophenone – benzhydrol – acetonitrile and acetone – isopropyl alcohol – acetonitrile systems were studied by laser flash photolysis transient absorption technique and by steady‐state quantum yield determinations. Kinetic parameters were derived for reactions of the ketyl radicals formed in the primary photoreduction steps. The room temperature overall rate coefficients at 0.001 mol dm−3 benzophenone and 2.6 mol dm−3 isopropyl alcohol in acetonitrile are in 108 dm3 mol−1 s−1 units: 12.8 ± 0.6, 8.0 ± 0.4 and 0.59 ± 0.01 for Mc2ĊOH + Me2ĊOH, Me2ĊOH + Ph2ĊOH and Ph2ĊOH + Ph2ĊOH, respectively. (The error limits represent 2 standard deviations.) Combination was shown to be the only significant reaction in the interaction of two Ph2ĊOH radicals, while disproportionation is the dominating path in the reactions inolving Me2ĊOH radicals. Evidences are presented for the existence of four reaction channels in the cross reaction of the two ketyl radicals. These are combination (4a), disproportionations (4b) and (4c) and formation of a “light absorbing transient” (4d), with branching ratios k4a/k4 = 0.18 ± 0.08, k4b/k4 = 0.61 ± 0.11, k4c/k4 = 0.05 ± 0.02 and k4d/k4 = 0.18 ± 0.03, respectively. – The radical transfer reaction Me2ĊOH + Ph2CO → Me2CO + Ph2ĊOH, which may change considerably the product distribution and quantum yields in the photoreduction of benzophenone by isopropyl alcohol at medium and low light intensities, was investigated by quantum yield determinations and a room temperature rate coefficient of k5 = (7.3 ± 1.2) · 104 dm3 mol−1 s−1 was extracted through computer model simulation. This rate coefficient is considerably lower than the values reported previously.

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Photoinduzierte H‐Abstraktionen an Benzylarylethern durch Benzophenon

1978

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Photoinduced H‐Abstraction on Benzyl Aryl Ethers by Benzophenone The triplet state of benzophenone abstracts in benzene of benzyl aryl ether 6 hydrogen atom from the CH2‐group. The formed α‐ether radicals 1 and diphenylhydroxymethyl radicals 8 react to form the three possible reaction products in statistical distribution. Benzaldehydes 2 and phenols 11 are formed in a side reaction. From quantum yield measurements of the benzophenone reduction in dependence upon the concentration of benzyl phenyl ether 6a follows a rate constant of the H‐abstraction of 9.5 ·105 M−1s−1 which is in good agreement with measurements in presence of naphthalene as a quencher. The quenching constant for benzophenone triplet by naphthalene is 2 · 109 M−1s−1. For benzyl phenyl ethers substituted in the benzyl ring the reaction constant for the H‐abstraction reaction was determined, ϱ = −0,68,

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CIDNP study of the photoreduction of benzophenone with secondary alcohols

Cited by 10 publications

References 33 publications

Electron transfer photoisomerization of norbornadiene to quadricyclane cosensitized by dibenzoylmethanatoboron difluoride and aromatic hydrocarbons

Electron transfer photoisomerization of norbornadiene to quadricyclane cosensitized by dibenzoylmethanatoboron difluoride and aromatic hydrocarbons

Kinetics of Ketyl Radical Reactions Occurring in the Photoreduction of Benzophenone by Isopropyl Alcohol

Photoinduzierte H‐Abstraktionen an Benzylarylethern durch Benzophenon

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