Chemical titration of thermally generated triplets

Adam, Waldemar; Cheng, Chen-Chih; Cueto, Omar; Sakanishi, Katsumasa; Zinner, K.

doi:10.1021/ja00499a068

Cited by 14 publications

(6 citation statements)

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“…The DA reaction rates of 1 with cycloheptatriene 5 and with cyclooctatetraene 7 are of particular interest. Hundreds of papers deal with the possible equilibrium and reactivity of the valence tautomers 5 17 and 7 20 [35][36][37][38][39][40]. The very active singlet oxygen 1 О 2 demonstrates a low selectivity in the DA reaction with 5, giving 95% of 1,4-adduct with the structure similar to 18, and about 5% with a structure similar to that of 15, whereas the less active and more selective dienophile 1 gives only the adduct 15 [41] (Schemes 2, 3).…”

Section: Participation Of the Active Tautomers 17 And 20 In The Da Rementioning

confidence: 99%

“…Therefore, throughout the temperature range 25-100°C in reaction 1 + 5 the formation only adduct 15 should be expected. Other reaction channels have been proposed [16,38,[52][53][54]. The [2π +2π +2π ]-cycloaddition of 1 at C 2 , C 5 atoms of nonconjugated norbornadiene is well known.…”

Section: Da Reaction Of 4-mentioning

confidence: 99%

“…The [2π +2π +2π ]-cycloaddition of 1 at C 2 , C 5 atoms of nonconjugated norbornadiene is well known. Assuming a similar cycloaddition of dienophile 1 at C 2 ,C 5 atoms of the nonconjugated, the sterically accessible coplanar system of triene 5, going through the transition state 19, the formation of adduct 15 can be suggested [16,38,[52][53][54] (Scheme 3). However, the rate constant of reaction 1 with triene 5 (entry 3, Table I) is almost two thousand times larger than that of 1 in the reaction with norbornadiene (entry 18, Table I).…”

Section: Da Reaction Of 4-mentioning

confidence: 99%

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Cyclic and Acyclic N═N Bonds in Reactions with Some Alkenes and Dienes

Kiselev

Kornilov

Коновалов

2017

Int. J. Chem. Kinet.

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The kinetics of the Diels–Alder (DA) reactions of 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione 1, trans‐diethyl azodicarboxylate 2, and tetracyanoethene 3 with 1,3‐cyclohexadiene 4, cycloheptatriene 5, 1,3‐cycloheptadiene 6, cyclooctatetraene 7, and 1,3‐cyclooctadiene 8 in a range of temperatures and pressures has been studied. Values of the enthalpy, entropy, and volume of activation, as well as the enthalpy and volume of reaction have been obtained. Observed reaction rates of 5+1 and 7+1 have been compared with the known rate of norcaradiene 17 formation in the equilibrium 5⇌17, and that of bicyclo[4,2,0]‐octa‐2,4,7‐triene 20 in the equilibrium 7⇌20. The kinetic data show that the rate of formation of 17 from 5 is much greater than the loss rate of dienophile 1 in reaction of 5+1. In contrast, the formation rate of tautomer 20 is less than the loss rate of dienophile 1 in reaction of 7+1. This reflects that the consecutive reaction of 5 → 17 (+1) → 15 is possible whereas the consecutive reaction of 7 → 20 (+1) → 22 does not occur as the only way.

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Section: Participation Of the Active Tautomers 17 And 20 In The Da Rementioning

confidence: 99%

Section: Da Reaction Of 4-mentioning

confidence: 99%

Section: Da Reaction Of 4-mentioning

confidence: 99%

See 1 more Smart Citation

Cyclic and Acyclic N═N Bonds in Reactions with Some Alkenes and Dienes

Kiselev

Kornilov

Коновалов

2017

Int. J. Chem. Kinet.

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“…21 With the triplet excited ketones, the excitation energy is transferred first to the naphthalene mediator, which may in turn transfer the excitation energy to a triplet excited state of the ligand set of {Eu} that then follows the same relaxation process 21. 22 An alternative method for determining the singlet/triplet ratio from dioxetanes is based on chemical titration, such as the reaction with fumaronitrile employed in the determination of the thermal singlet/triplet ratio of bis(adamantyl)dioxetane by Schuster et al,15 but the spin‐selective reactions employed are somewhat inefficient and typically require relatively high concentrations of excited ketone 23. Accurate determination of the singlet/triplet ratio in our mechanochemical system necessitated the superior sensitivity of the photophysical approach outlined above.…”

Section: Introductionmentioning

confidence: 99%

Dioxetane Scission Products Unchanged by Mechanical Force

Clough

Sijbesma

2014

ChemPhysChem

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Dioxetane-based force-induced light emission from polymers, or mechanoluminescence, is a powerful new way of characterizing the behavior of polymeric materials under stress. Here, we reveal that breaking the dioxetane mechanically gives strikingly similar products to those formed on thermal activation, with a singlet/triplet ratio of 1:9.9 and a total quantum yield of 9.8%. A sensitized relay scheme ensured high reproducibility in the detection of the short-lived triplet products. In addition to guiding the design of more sensitive mechanoluminescent probes, the similarity in the scission products indicates that once mechanical force releases the steric lock between the adamantyl groups, the dioxetane undergoes scission in a pathway that resembles the thermal process. Excited states are formed only after the main transition state in a region in which the excited- and ground-state surfaces are nearly degenerate, which, thus, accounts for the remarkable similarity in the scission products.

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“…Again, this result is inconclusive as far as the mechanism of dioxetane decomposition is concerned, because either the diradical (9-DR) is not formed or if it is formed, it fragments faster than valence-isomfljng to diradical (l0-DR), Heavy atom effects Since 1,Z-dioxetanes selectively chemi-energize triplet states ($T/$S large, Table 1), a spin-forbidden reaction is involved in this process in which a ground state hyperenergetic molecules decomposes thermally into a triplet state excited product (eqn. 20), In such intersystem-crossing reactions spinThermal generation of electronic excitation 2603 orbit coupling is one of the principal mechanisms of action, which is promo-SR T* (20) ted through "heavy atom" perturbations (Ref. 34).…”

Section: Isotope Effectsmentioning

confidence: 99%

Thermal generation of electronic excitation with hyperenergetic molecules

Adam¹

1980

Pure and Applied Chemistry

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Abstract-The synthesis of a large variety of hyperenergetic molecules such as the 1,2-dioxetanes, u-peroxylactones, 3-imino-l, 2-dioxetanes, benzo-l,4-dioxin dioxetanes, bisdioxetanes, u-pyrone endoperoxides and cyclic peroxalates are presented. The utilization of these unique substances for the thermal generation of electronically excited states is reviewed, with special reference to the total excitation yield ($T+S) and spin state selectivities ($T/$S), The physical and chemical methods for the determination of excitation yields are discussed and scrutinized for their reliability and effectiveness, Mechanistic problems such as energy transfer, heavy atom effects, electron exchange, etc. are analyzed. The biological implications of such "high energy" molecules is emphasized.

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Chemical titration of thermally generated triplets

Cited by 14 publications

References 1 publication

Cyclic and Acyclic N═N Bonds in Reactions with Some Alkenes and Dienes

Cyclic and Acyclic N═N Bonds in Reactions with Some Alkenes and Dienes

Dioxetane Scission Products Unchanged by Mechanical Force

Thermal generation of electronic excitation with hyperenergetic molecules

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