Quenching and radical formation in the reaction of photoexcited benzophenone with thiols and thio ethers (sulfides). Nanosecond flash studies

Inbar, Shai; Linschitz, Henry; Cohen, Saul G.

doi:10.1021/ja00370a038

Cited by 52 publications

(19 citation statements)

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“…Interestingly, although the ionization potentials vary over a range of ca 0.3 eV for the secondary aliphatic amines, the quenching rate constants remain nearly constant except for 2,2,6,6-tetramethylpiperidine (6) and diisopropylamine (8). This insensitivity to the donor strength may indicate that the 'direct' hydrogen transfer pathway k dir NH dominates.…”

Section: Quenching By Secondary Aminesmentioning

confidence: 97%

Quenching of n,?*-excited azoalkanes by amines: structural and electronic effects on charge transfer

Pischel

Nau

2000

J. Phys. Org. Chem.

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Section: Quenching By Secondary Aminesmentioning

confidence: 97%

Quenching of n,?*-excited azoalkanes by amines: structural and electronic effects on charge transfer

Pischel

Nau

2000

J. Phys. Org. Chem.

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“…It is well-known that reaction by the ET-PT (22,23) and charge-transfer assisted (12,13) mechanisms proceeds with enhanced rates as solvent polarity increases. In contrast, reaction by the HBX-EPT mechanism can be expected to be faster in solvents of low polarity, because hydrogen bonding is favored in nonpolar solvents.…”

Section: Discussionmentioning

confidence: 99%

Geometric and solvent effects on intramolecular phenolic hydrogen abstraction by carbonyl n,π* and π,π* triplets

Lathioor¹,

Leigh²

2001

Can. J. Chem.

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The photochemistry of a series of alkoxyacetophenone, -benzophenone, and -indanone derivatives, which contain a remote phenolic group linked to the ketone by a para,para¢-or meta,meta¢-oxyethyl spacer, has been studied in acetonitrile and dichloromethane solutions using laser flash photolysis techniques. The corresponding methoxysubstituted compounds and, in the case of the alkoxyindanones, derivatives bearing just a remote phenyl substituent, have also been examined. The triplet lifetimes of the phenolic compounds are determined by the rates of intramolecular abstraction of the remote phenolic hydrogen, and depend on the solvent, the geometry of attachment and the configuration of the lowest triplet state. In contrast to the large (>500-fold) difference in lifetime of the para,para¢-and meta,meta¢-alkoxyacetophenone derivatives, both of which have lowest p,p* triplet states, smaller differences are observed for the alkoxyindanone (lowest charge transfer triplet,~twofold difference) and alkoxybenzophenone (lowest n,p* triplet,~18-fold difference) derivatives in acetonitrile solution. The triplet lifetimes of the acetophenone and benzophenone are significantly shorter in dichloromethane than in acetonitrile, consistent with the intermediacy of a hydrogen-bonded triplet exciplex in the reaction. This is not the case with the para,para¢-indanone derivative, sugesting that hydrogen abstraction in this compound is dominated by a mechanism involving initial charge transfer rather than hydrogen bonding. This is most likely due to orientational constraints that prevent the remote phenolic -O-H group from adopting a coplanar arrangement with the n-orbitals of the carbonyl group.Résumé : Faisant appel à des techniques de photolyse éclair au laser et opérant dans des solutions d'acétonitrile et de dichlorométhane, on a étudié la photochimie d'une série de dérivés alkoxyacétophénones, -benzophénones et -indanones comportant un groupe phénolique dans une position éloignée, mais liée à la cétone par un espaceur oxyéthyle en para,para¢-ou méta,méta¢-. On a aussi étudié les composés correspondants portant des substituants méthoxy ainsi que, dans le cas des alkoxyindanones, des dérivés ne portant qu'un substituant phényle en position éloignée. On a déterminé les temps de vie du triplet des composés phénoliques à partir des vitesses d'enlèvement intramoléculaire de l'hydrogène phénolique éloigné; ils dépendent du solvant, de la géométrie de fixation et de la configuration de l'état triplet le plus bas. Par opposition à la grande différence (>500 fois) dans les temps de vie des dérivés para,para¢-et méta,méta¢-alkoxyacétophénones qui ont tous les deux des états triplets p,p* plus faibles, on observe des différences plus faibles pour les dérivés alkoxyindanones (triplet de transfert de charge le plus faible; différence du simple au double) et alkoxybenzophénones (triplet n,p* le plus faible; différence correspondant à une réaction environ 18 fois plus rapide) dans une solution d'acétonitrile. Les temps de vie des dérivés de l'acétop...

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“…Moreover, GSH efficiently quenches triplet carbonyls (6.7 x 10 s M-Is -I) by a reaction involving its SH group. The quenching process seems to proceed by a charge transfer complex followed by H abstraction from the S-H bond and/or from the a-carbon atom [64]. Other thiol-containing compounds, such as cysteine, methionine, and GSSG, also quench triplet carbonyls efficiently (kQ = 3.2-, 35-, and 13 x 10 s M-Is -1, respectively).…”

Section: Hi Deactivation Of the Excited Statementioning

confidence: 99%

The role of singlet oxygen and triplet carbonyls in biological systems

Durán

Cadenas

1987

Reviews of Chemical Intermediates

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Quenching and radical formation in the reaction of photoexcited benzophenone with thiols and thio ethers (sulfides). Nanosecond flash studies

Cited by 52 publications

References 0 publications

Quenching of n,?*-excited azoalkanes by amines: structural and electronic effects on charge transfer

Quenching of n,?*-excited azoalkanes by amines: structural and electronic effects on charge transfer

Geometric and solvent effects on intramolecular phenolic hydrogen abstraction by carbonyl n,π* and π,π* triplets

The role of singlet oxygen and triplet carbonyls in biological systems

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