IMPORTANCE OF NEIGHBORING GROUP PARTICIPATION IN THE REMARKABLY RAPID PHOTOREDUCTION OF 1,1,4,4‐TETRAMETHYL‐l,4‐DIHYDRO‐2,3‐NAPHTHALENEDIONE#

Scaiano, J. C.; Wintgens, Véronique; Netto‐Ferreira, José Carlos

doi:10.1111/j.1751-1097.1989.tb02899.x

Cited by 14 publications

(10 citation statements)

References 15 publications

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“…Hydrogen abstraction rate constants were also measured for the reaction of the b-lapachones triplet 1-3 with 1,4-cyclohexadiene, a very efficient hydrogen donor, 38 for which the values obtained are in the range 10 5 -10 6 L mol −1 s −1 (Table 1). These rate constants are much slower than those observed for typical np* mono or diketones, such as benzophenone 38 or 1,1,4,4-tetramethyl-1,4-dihydro-2,3-naphthalenedione, 39 respectively, which are remarkably fast (>10 8 L mol −1 s −1 ), being comparable to those for other pp* ketones such as dinaphthylketones. 40 It is well known that the hydrogen abstraction rate constant of some ortho-quinones from 2-propanol, such as phenanthrenequinone, 33- 35 1,2-naphthoquinone 35,36 and 4,5-pyrenequinone, 37 is dependent on the solvent polarity.…”

Section: Resultsmentioning

confidence: 60%

Laser flash photolysis study of the triplet reactivity of β-lapachones

Netto‐Ferreira

Bernardes

Ferreira

et al. 2008

Photochem Photobiol Sci

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The photochemical reactivity of beta-lapachone (1), nor-beta-lapachone (2) and beta-lapachone 3-sulfonic acid (3) has been examined by laser flash photolysis. Excitation (lambda = 266 nm) of degassed solutions of , in acetonitrile or dichloromethane, resulted in the formation of detectable transients with absorption maxima at 300, 380 and 650 nm. These transients, with lifetimes of 5.0 micros, were quenched by beta-carotene at a diffusion-controlled rate constant and assigned to the triplet excited states of 1-3. Addition of hydrogen donors, such as 2-propanol, 1,4-cyclohexadiene, 4-methoxyphenol or indole led to the formation of new transients, which were assigned to the corresponding ketyl radicals obtained from the hydrogen abstraction reaction by the triplets 1-3 . In the presence of triethylamine it was observed the formation of the long-lived anion radical derived from , which shows absorption maxima at 300 and 380 nm. The low values observed for the hydrogen abstraction rate constants for the beta-lapachones 1-3 using 2-propanol and 1,4-cyclohexadiene as quenchers led us to conclude that their triplet excited states show pi pi* character.

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Section: Resultsmentioning

confidence: 60%

Laser flash photolysis study of the triplet reactivity of β-lapachones

Netto‐Ferreira

Bernardes

Ferreira

et al. 2008

Photochem Photobiol Sci

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“…[22][23][24] Taking as an example the quenching rate constant, (1.8 ± 0.2) × 10 8 L mol -1 s -1 ), for the hydrogen abstraction from 1,4-cyclohexadiene (a very efficient hydrogen donor), one can observe that this value is remarkably fast and comparable to those obtained for typical np* mono or diketones, such as benzophenone 21 or 1,1,4,4-tetramethyl-1,4-dihydro-2,3-naphthalenedione. 25 For comparison, ketones such as dinaphthylketones, having lowest energy triplet with pp* character, show quenching rate constant by 1,4-cyclohexadiene of ca. 10 6 L mol -1 s -1 .…”

Section: Resultsmentioning

confidence: 99%

Laser flash photolysis study of the photochemistry of thioxanthone in organic solvents

Rodrigues¹,

Silva²,

Netto‐Ferreira³

2010

J. Braz. Chem. Soc.

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A fotorreatividade do estado excitado triplete de tioxantona (TX) foi investigada empregando a técnica de fotólise por pulso de laser. O máximo do comprimento de onda de absorção e o tempo de vida para o seu estado excitado triplete são dependetes do solvente. Quando foram utilizados solventes doadores de hidrogênio, foi observado o surgimento de uma nova banda no espectro de absorção para os transientes, com máximo a 410 nm, a qual foi atribuída ao radical cetila derivado da tioxantona. As constantes de velocidade de supressão para o triplete de tioxantona, k q , variaram de (1,7 ± 0,1) × 10 6 L mol -1 s -1 para tolueno a ca. 10 9 L mol -1 s -1 para fenol e seus derivados contendo substituintes poleres, bem como para indol, trietilamina e DABCO.The photoreactivity of the triplet excited state of thioxanthone (TX) was investigated employing the laser flash photolysis technique. The wavelength for the absorption maximum and the lifetime of the triplet excited state are solvent dependent. When hydrogen donor solvents were employed, a new band at 410 nm was observed in the triplet absorption spectrum, which was attributed to the ketyl radical derived from thioxantone. Quenching rate constants, k q , ranged from (1.7 ± 0.1) × 10 6 L mol -1 s -1 for toluene to ca. 10 9 L mol -1 s -1 for phenol and its derivatives containing polar substituents, as well as for indole, triethylamine and DABCO.

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“…1 On the other hand, 1,1,4,4-tetramethyl-1,4-dihydro-2,3-naphthalendione, which has also a low lying n * triplet state, shows remarkably fast hydrogen abstraction rate constants. 2 Despite its low triplet energy (E T = 230 kJ mol -1 ) 2 the reaction rate constant for the latter diketone in the presence of hydrogen donor exceeds that of triplet benzophenone. 3 Large hydrogen abstraction rate constants were also found for acenaphthenequinone, for which rate constant values ranging from 6.2x10…”

Section: Introductionmentioning

confidence: 99%

“…This extra stabilization occurs through intramolecular hydrogen bonding between the hydroxyl group and its vicinal carbonyl. 2 Ketones having a low energy triplet state with * character are much less reactive towards aliphatic or benzylic hydrogen abstraction than those with n * character. 5 Thus, examples of * ketones for which hydrogen abstraction rate constants could be measured, such as 1,1'-, 1,2'-and 6 The -dicarbonyl compounds 1,2-naphthalenedione and 9,10-phenanthrenequinone show triplet reactivity, which is dependent on the solvent polarity.…”

Section: Introductionmentioning

confidence: 99%

Laser flash photolysis study of the phenolic hydrogen abstraction by 1,2-aceanthrylenedione triplet

Serra

Lucas

Netto‐Ferreira

2004

J. Braz. Chem. Soc.

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A técnica de fotólise por pulso de laser de nanossegundo foi empregada no estudo da reatividade do triplete de 1,2-aceantrilenodiona (1) ), assim como o fato de que a constante de velocidade de supressão por -caroteno é controlada por difusão, sugerem que a energia do triplete de energia mais baixa para 1,2-aceantrilenodiona situa-se entre 88 e 219 kJ mol -1 .The nanosecond laser flash photolysis technique has been used to study the reactivity of 1,2-aceanthrylenedione (1) triplet towards phenols. Using acetonitrile as solvent, the quenching rate constant k q ranged from 3.3 x 10 5 L mol -1 s -1 (phenol) to 1.3 x 10 7 L mol -1 s -1 (4-hydroxyphenol). Phenols with electron donating substituents were more reactive. The kinetic isotope effect (k H /k D ) observed for the quenching of 1 with 4-methoxyphenol was 1.5. The Hammett plot for the reaction of the triplet of 1 with phenols gave a reaction constant = -1.04 in acetonitrile solution. The low value for the quenching rate constant measured for this triplet with 1,3-cyclohexadiene (k q =2.0 x 10 4 L mol ) and the diffusion controlled quenching rate constant obtained for -carotene suggest that the energy of the lowest triplet state for 1,2-aceanthrylenedione is located between 88 and 219 kJ mol -1 .

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IMPORTANCE OF NEIGHBORING GROUP PARTICIPATION IN THE REMARKABLY RAPID PHOTOREDUCTION OF 1,1,4,4‐TETRAMETHYL‐l,4‐DIHYDRO‐2,3‐NAPHTHALENEDIONE#

Cited by 14 publications

References 15 publications

Laser flash photolysis study of the triplet reactivity of β-lapachones

Laser flash photolysis study of the triplet reactivity of β-lapachones

Laser flash photolysis study of the photochemistry of thioxanthone in organic solvents

Laser flash photolysis study of the phenolic hydrogen abstraction by 1,2-aceanthrylenedione triplet

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