Flash-photolysis generation and reactivities of triarylmethyl and diarylmethyl cations in aqueous solutions

McClelland, Robert A.; Kanagasabapathy, V. M.; Banait, Narinder S.; Steenken, S.

doi:10.1021/ja00193a031

Cited by 150 publications

(142 citation statements)

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“…While the effect of each additional substituent is not additive, each para-methoxy group significantly decreases the rate of reaction of the cation (9).…”

Section: Discussionmentioning

confidence: 95%

“…Consequently, the observed lack of carbon-carbon bond cleavage upon photosensitized (electron transfer) irradiation of 11 and 12 (reactions [8] and [9]) can be explained on therrnodynamic grounds.…”

Section: Discussionmentioning

confidence: 99%

“…Irradiation of methyl 2-(4-methoxypheny1)-2-phenylethyl ether (12) in the acetonitrile-methanol-0-d solution leads to relatively efficient deuterium incorporation at the bis-benzylic position (reaction [9]). No carbon-carbon bond cleavage was observed.…”

Section: A*mentioning

confidence: 99%

“…The radical cations of the para-methoxy derivatives, 12, 14, and the model compound 17, undergo deprotonation as evidenced by deuterium incorporation and, in the case of 14, isomerization (reactions [9], [ l 11 , and [ 131). Deprotonation from the radical cations of these para derivatives must be rapid enough to compete with deactivation by back-electron transfer (Scheme 3, step 3).…”

Section: Deprotonation Of the Radical Cationmentioning

confidence: 99%

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The effect of meta- and para-methoxy substitution on the reactivity of the radical cations of arylalkenes and alkanes. Radical ions in photochemistry. Part 26

Arnold¹,

Du²,

Henseleit³

1991

Can. J. Chem.

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. Can. J. Chem. 69,839 (1991). The effect of mera-and para-methoxy substitution on the reactivity of some radical cations has been determined. The compounds chosen for study were 1-(3-methoxypheny1)-1-phenylethylene (7), 1-(4-methoxypheny1)-1-phenylethylene (S), 3-(3-methoxypheny1)indene (9), 3-(4-methoxypheny1)indene (lo), methyl 2-(3-methoxypheny1)-2-phenylethyl ether ( l l ) , methyl 2-(4-methoxypheny1)-2-phenylethyl ether (l2), cis-and trans-2-methoxy-1-(3-methoxypheny1)indane (13), and cis-and trat1s-2-methoxy-l-(4-methoxyphenyl)indane (14). The radical cations of these compounds were generated by photosensitization (electron transfer) using 1,4-dicyanobenzene (3) as the electron acceptor. The three reactions studied were: (1) The addition of nucleophiles (methanol) to the radical cation of the arylalkenes, a reaction that yields the anti-Markovnikov addition product.(2) The carbon-carbon bond cleavage of radical cations, which yields products derived from the radical and carbocation fragments. (3) The deprotonation of the radical cation, a reaction that can be used to invert the configuration at a saturated carbon centre. The mechanisms of these reactions are discussed and the factors that need to be considered in order to predict reactivity are defined. Molecular orbital calculations (UHFISTO-3G) were carried out on the radical cations of the model compounds 3-and 4-vinylanisole and 3-and 4-methylanisole.Key words: photochemistry, photosensitize (electron transfer), radical cation, radical DONALD R. ARNOLD, XINYAO DU et KERSTIN M. HENSELEIT. Can. J. Chem. 69,839 (1991). On a dttermint l'effet de substituants en me' ta et en para sur la rCactivitC de quelques radicaux cations. Les composCs choisis pour cette ttude sont : les 1-(3-mtthoxyphtny1)-1-phtnylCthyl&ne (7), 1 -(4-mCthoxyphtny1)-1 -phtnyltthylkne (S), 3-(3-mtthoxyphtny1)indkne (9), 3-(4-mtthoxyphtnyl)ind&ne (lo), 1-mtthoxy-2-(3-mtthoxyphtny1)-2-phCnyltthane ( l l ) , I-mtthoxy-2-(4-mCthoxyphtny1-2-phtnyltthane (12), les cis-et trans-2-mtthoxy-I-(3-mtthoxyphtny1)indane (13) et les cis-et trans-2-mtthoxy-1-(4-mtthoxyphtny1)indane (14). On a gCnCrC les cations radicaux de ces composts par photosensibilisation (transfert d'Clectron), en utilisant le 1,4-dicyanobenzkne (3) comme accepteur d'tlectrons. Les trois rtactions ttudites sont: (1) l'addition de nuclCophiles (methanol) aux cations radicaux des arylalcknes, une rtaction qui conduit ?I un produit d'addition anti-Markovnikov; (2) le clivage de la liaison carbone-carbone des cations radicaux qui conduit ?I des produits qui dtrivent des fragments radicalaires et carbocationiques et (3) la dtprotonation des cations radicaux qui peut Ctre utiliste pour inverser la configuration ?I un site carbon6 saturt. On discute des mCcanismes de ces rkactions et on dtfinit les facteurs qu'il faut considtrer afin de pouvoir prtdire la rtactivitC. On a effectut des calculs d'orbitales moltculaires (UHF/ STO-3G) sur les cations radicaux des composts modkles, 3-et 4-vinylanisole et 3-et 4-mtthylanisole.

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“…While the effect of each additional substituent is not additive, each para-methoxy group significantly decreases the rate of reaction of the cation (9).…”

Section: Discussionmentioning

confidence: 95%

Section: Discussionmentioning

confidence: 99%

Section: A*mentioning

confidence: 99%

Section: Deprotonation Of the Radical Cationmentioning

confidence: 99%

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The effect of meta- and para-methoxy substitution on the reactivity of the radical cations of arylalkenes and alkanes. Radical ions in photochemistry. Part 26

Arnold¹,

Du²,

Henseleit³

1991

Can. J. Chem.

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“…The rate of addition of methanol to the radical cation la", within the methanol-solvation cage of the radical-ion pair, has been measured (3 x lo9 s-' (12)). Methoxy substitution greatly retards this reaction; the addition of methanol to the radical cation of 1,l-dianisylethylene has been estimated to be 10' M-I s-', almost two orders of magnitude slower than the addition to la" (12)(13)(14). This is clearly a reflection of the reduced positive charge density on the terminal carbon of the alkene; the positive charge is largely associated with the para-methoxy groups.…”

Section: The Addition Of Nucleophiles To the Radical Cations Of Arylamentioning

confidence: 99%

The effect of meta- or para-cyano substitution on the reactivity of the radical cations of arylalkenes and alkanes. Radical ions in photochemistry, Part 34

Arnold¹,

Du²,

Chen³

1995

Can. J. Chem.

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The effect of electron-withdrawing substituents, mera-orpnr~l-cyano, on the rcactivity of the radical cation of arylalkenes and alkanes has been determined. The radical cations were generated by single electron transfer (set) to an electron-accepting photosensitizer. Three reactions were studied: (i) the addition of nucleophile to the radical cation of arylalkenes, (ii) cleavage of the benzylic carbon-carbon bond of the radical cation of arylalkanes; and (iii) the deprotonation of the benzylic carbon-hydrogen bond of the radical cation of arylalkanes. The radical cations of 4-(1-pheny1ethenyl)benzonitrile (lb), 3-(1-phenylethenyl)benzonitrile (lc), 4-(2-methoxy-I-phenylethy1)benzonitrile (20). 3-(2-methoxy-I-phenylethy1)benzonitrile ( 2~) .cis-and tr.crrls-5-cyano-2-methoxy-1-phenylindane (60-cis and -rratls), and 6-cyano-3-phenylindene (7B) were generated, by single electron transfer to the lowest excited singlet state of 1,4-dicyanobenzene (3), in acetonitrile-methanol. The radical cations of lb, lc, and 70 react with methanol to yield the nrzri-Markovnikov adducts (20,2c, and 60-cis and 60-rmns). The radical cations of 2 0 . 2~. and 60-rrcrrzs cleave at the benzylic carbonsarbon bond to give products derived from the radical and carbocation fragments. The radical cation of 60-cis deprotonates from the benzylic position with subsequent formation of the diastereomer, 60-rrarls. This behaviour can be explained1 predicted on the basis of the proposed mechanisms for these reactions. Molecular orbital calculations (AM 1) support the conclusions.Key words: photosensitized, electron transfer, radical ions, radicals, molecular orbital calculations (AMI).RCsumC : On a dCterminC I'effet de substituants Clectroattracteur, les groupes rrle'ra-et pcrrcr-cyano, sur la rCactivitC de cations radicaux d'arylalcknes et alcanes. On a gCnCrC les cations radicaux par le transfert d'un seul Clectron i un photosensibilisateur accepteur d'klectron. On a CtudiC trois rCactions : (i) l'addition d'un nuclCophile sur le cation radical des arylalcknes; (ii) le clivage de la liaison carbone-carbone benzylique du cation radical des arylalcanes et (iii) la dCprotonation de la liaison carbone-hydrogkne benzylique du cation radical des arylalcanes. On a gCnCrC les cations radicaux des 4-(1-phCnylCthCny1)benzonitrile (10). 3-(1-phCnylCthCny1)-benzonitrile (lc), 4-(2-mCthoxy-1-phCny1Cthyl)benzonitrile (20). 3-(2-mCthoxy-I-phCnylCthy1)benzonitrile (2c), cis-et r,nr1~-5-cyan0-2-mCthoxy-I -phCnylindane (6b-cis et -fmrls) et 6-cyano-3-phCnylindkne (70) par un transfert d'un seul Clectron j. l'Ctat singulet excite le plus bas du 1,4-dicyanobenzkne (3), en solution dans l'acCtonitrile-mCthano1. Les cations radicaux des composCs lb, l c et 70 rkagissent avec le methanol pour donner des adduits arlri-Markovnikov (2b, 2c et 60-cis et 60-rrarls). Les radicaux cations 2 0 . 2~ et 60-rrans se clivent au niveau de la liaison carbone-carbone benzylique pour donner des produits dCrivCs des fragments radicalaires et carbocationiques. Le cation radica...

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Intramolecular reactivity of arylcarbenes: Biphenyl-2-ylcarbenes

Dorra

Gomann

Guth

et al. 1996

J. Phys. Org. Chem.

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Biphenyl-2-ylcarbenes, 2-ArC6H,CR, were generated photolytically and thermally from diazo precursors. Cyclization, leading to fluorenes, competes with capture of the carbenes by methanol but proceeds faster than intramolecular hydrogen shifts (with R = Me) and intermolecular C-H insertion reactions (with R = H in cyclohexane). By comparison of product ratios with kinetic data for related carbenes from the literature, the cyclization rate is estimated as cu 10" s-'. The intramolecular reactivity of biphenyl-2-ylcarbenes is not significantly attenuated by variation of R (R = H, Me, Ph). Very minor effects of triplet sensitization and methanol quenching indicate that fluorenes arise from spin-equilibrated biphenyl-2-ylcarbenes, presumably from the singlet state. When A r = mesityl, the carbene predominantly inserts into C-H bonds of the 2'-methyl groups, giving rise to a dihydrophenanthrene. Formation of a fluorene derivative, by formal insertion into C-C bonds, occurs as a minor process. This unprecedented reaction points to intervention of an o-xylylene in which the methyl group migrates. Laser flash photolysis (LFP) of 2-PhC6H,CN,Ph generates a transient absorption which is due to the To -+ T, transition of 9-phenylfluorene rather than to the presumed o-xylylene. On LFP of 2-ArC,H,CN,Ph in trifluoroethanol-acetonitrile, protonation of the carbenes gives rise to carbocations, 2-ArC,H,CH 'Ph. The transient absorption spectra of these cations are strongly influenced by twisting about the Ar-Ar bond (Ar = P h i o-tolyl< mesityl) whereas the rates of nucleophilic capture vary only slightly. Biphenyl-2-ylcarbenium ions (Ar = R = Ph) cyclize more slowly than the analogous carbenes, by a factor of 310,.

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Flash-photolysis generation and reactivities of triarylmethyl and diarylmethyl cations in aqueous solutions

Cited by 150 publications

References 1 publication

The effect of meta- and para-methoxy substitution on the reactivity of the radical cations of arylalkenes and alkanes. Radical ions in photochemistry. Part 26

The effect of meta- and para-methoxy substitution on the reactivity of the radical cations of arylalkenes and alkanes. Radical ions in photochemistry. Part 26

The effect of meta- or para-cyano substitution on the reactivity of the radical cations of arylalkenes and alkanes. Radical ions in photochemistry, Part 34

Intramolecular reactivity of arylcarbenes: Biphenyl-2-ylcarbenes

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