Chemistry of the biradicals produced in the Norrish Type II reaction

Scaiano, J. C.; Lissi, E. A.; Encina, M. V.

doi:10.1007/bf03155998

Cited by 60 publications

(33 citation statements)

References 235 publications

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“…Such a large variation in the relative rate constants for cleavage and coupling of the putative 1,4-biradicaloid intermediates is surprising. The two main factors that should affect the partitioning of such species between cleavage and coupling are the relative thermodynamic stabilities of the coupling and cleavage products and the conformational preferences of the 1,4-biradical as they are reflected in the relative transition state energies for cleavage and coupling (37)(38)(39)(40)(41). In the present cases, thermodynamics would clearly be expected to strongly favor coupling over cleavage in all cases.…”

Section: Discussionmentioning

confidence: 75%

Steady state and time-resolved spectroscopic studies of the photochemistry of 1-arylsilacyclobutanes and the chemistry of 1-arylsilenes

Leigh¹,

Boukherroub²,

Bradaric³

et al. 1999

Can. J. Chem.

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Direct photolysis of 1-phenylsilacyclobutane and 1-phenyl-, 1-(2-phenylethynyl)-, and 1-(4'-biphenylyl)-1-methylsilacyclobutane in hexane solution leads to the formation of ethylene and the corresponding 1-arylsilenes, which have been trapped by photolysis in the presence of methanol. Quantum yields for photolysis of the three methyl-substituted compounds have been determined to be 0.04, 0.26, and 0.29, respectively, using the photolysis of 1,1-diphenylsilacyclobutane Φsilene = 0.21) as the actinometer. The corresponding silenes have been detected by laser flash photolysis; they have lifetimes of several microseconds, exhibit UV absorption maxima ranging from 315 to 330 nm, and react with methanol with rate constants on the order of (2-5) × 109 M-1 s-1 in hexane. Absolute rate constants for reaction of 1-phenylsilene and 1-methyl-1-phenylsilene with water, methanol, tert-butanol, and acetic acid in acetonitrile solution have been determined, and are compared to those of 1,1-diphenylsilene under the same conditions. With the phenylethynyl- and biphenyl-substituted methylsilacyclobutanes, the triplet states can also be detected by laser flash photolysis, and are shown to not be involved in silene formation on the basis of triplet sensitization and (or) quenching experiments. Fluorescence emission spectra and singlet lifetimes have been determined for the three 1-aryl-1-methylsilacyclobutanes, 1,1-diphenylsilacyclobutane, and a series of acyclic arylmethylsilane model compounds. These data, along with the reaction quantum yields, allow estimates to be made of the rate constants for the excited singlet state reaction responsible for silene formation. 1-Methyl-1-phenylsilacyclobutane undergoes reaction from its lowest excited singlet state with a rate constant 10-80 times lower than those of the other three derivatives. The results are consistent with a stepwise mechanism for silene formation, involving a 1,4-biradicaloid intermediate that partitions between product and starting material.Key words: silene, silacyclobutane, photochemistry, biradical.

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Section: Discussionmentioning

confidence: 75%

Steady state and time-resolved spectroscopic studies of the photochemistry of 1-arylsilacyclobutanes and the chemistry of 1-arylsilenes

Leigh¹,

Boukherroub²,

Bradaric³

et al. 1999

Can. J. Chem.

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“…The mechanism of the photoreaction of 2-oxoacetates [89][90][91][92] is based on a Norrish type II process, 93,94 which has been studied in quite some detail for many different structures. 95,96 As a first step, irradiation of 2-oxoacetates at 350-370 nm in polar and apolar solutions generates the excited triplet state of the photosensitive carbonyl group. Intramolecular γ-hydrogen abstraction then produces a 1,4-biradical (i) which, in argon saturated solution, forms the carbonyl compound and a hydroxy ketene (ii), the latter of which finally loses carbon monoxide to form an aldehyde (Scheme 8).…”

Section: -Oxoacetatesmentioning

confidence: 99%

Using photolabile protecting groups for the controlled release of bioactive volatiles

Herrmann

2012

Photochem Photobiol Sci

102

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To develop their biological activity, bioactive volatile compounds, such as pheromones or fragrances, have to evaporate from surfaces. Because these surfaces are usually exposed to natural daylight, the preparation of non-volatile precursors using photoremovable protecting groups is an ideal tool to control the release of caged volatile molecules from various surfaces by light-induced covalent bond cleavage. Many photoreactions occur under mild environmental conditions and are highly selective. To break covalent bonds under typical application conditions, the photoreaction has to proceed at ambient daylight, to tolerate the presence of oxygen and to run in polar media (e.g. in water). The amount of volatiles generated from photochemical delivery systems depends on the light intensity to which the systems are exposed. Both photoisomerisations and photofragmentations have successfully been investigated for the slow release of caged pheromones and fragrances from their corresponding precursors.

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“…In this state of aromatic ketones, have been the subject of study we use nanosecond laser flash photolysis considerable attention (1)(2)(3)(4). While their behavior techniques in an attempt to answer some of these in homogeneous solution is relatively well under-questions.…”

Section: Introductionmentioning

confidence: 99%

Dynamic aspects of the behavior of aromatic ketone triplets in anionic micelles. A laser flash photolysis study

Scaiano¹,

Selwyn²

1981

Can. J. Chem.

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The behavior of several aromatic ketone triplets has been examined in sodium dodecyl sulfate micelles using laser flash photolysis techniques. The molecules examined, acetophenone, propiophenone, isobutyrophenone, p-methoxyacetophenone, benzophenone, and xanthone are mainly resident in the micellar phase. Phenyl alkyl ketones show considerable self-quenching, a process that is rather sensitive to steric factors. All the molecules examined seem to reside near the Stern layer. Typical rate constants for triplet state entry into the micelle are around 1.8 × 1010 M−1 s−1.

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Chemistry of the biradicals produced in the Norrish Type II reaction

Cited by 60 publications

References 235 publications

Steady state and time-resolved spectroscopic studies of the photochemistry of 1-arylsilacyclobutanes and the chemistry of 1-arylsilenes

Steady state and time-resolved spectroscopic studies of the photochemistry of 1-arylsilacyclobutanes and the chemistry of 1-arylsilenes

Using photolabile protecting groups for the controlled release of bioactive volatiles

Dynamic aspects of the behavior of aromatic ketone triplets in anionic micelles. A laser flash photolysis study

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