<b>Production and Reactions of Methylene in the Triplet State</b>

Duncan, F. J.; Cvetanović, R. J.

doi:10.1021/ja00877a043

Cited by 51 publications

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“…Binding affinities. Photolytic decomposition of the excited states of ketene and diazomethane has been used as a source of 3 CH 2 [2]. In triplet H 2 CCO, the C-C adiabatic bond dissociation energy forming 3 CH 2 and 1 CO is calculated to be 88.3 kJ/mol at the QCISD(T)/cc-pVQZ//B3LYP/cc-pVQZ level of theory [48], consistent with the expected weak binding in this system.…”

Section: Energeticssupporting

confidence: 53%

“…The formally doubly bonded H 2 C5 5B-F is logically a closed-shell singlet, analogous to the isoelectronic diazomethane and ketene. The corresponding triplet, roughly drawn as the biradical H 2 C -B -F, is expected to be a weakly bound, excited state corresponding to the excited states of diazomethane and ketene en route to triplet CH 2 as they photolytically dissociate [2]. The structurally related carbene H 2 B-C-F with the boron and carbon transposed is plausibly a ground state triplet as we recognize this species to be a substituted derivative of the parent carbene, CH 2 .…”

Section: Introductionmentioning

confidence: 86%

“…The latter three structures have no singlet counterparts. The only four-coordinated carbon atom is found in 10 BC(H) 2 F, which is related to S3 BC(H) 2 hydrogen-bonded complexes, with its connection between HF and the medial fragment atom and consequent T-shaped structure. When the triatomic HBC is the proton acceptor (13 and 14), only FHÁ Á ÁC hydrogen bonds are observed.…”

Section: Minimamentioning

confidence: 98%

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The structure and energetics of triplet [B, C, F, H2]

Deakyne

Thomas

Liebman

2009

Journal of Fluorine Chemistry

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Section: Energeticssupporting

confidence: 53%

Section: Introductionmentioning

confidence: 86%

Section: Minimamentioning

confidence: 98%

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The structure and energetics of triplet [B, C, F, H2]

Deakyne

Thomas

Liebman

2009

Journal of Fluorine Chemistry

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“…This dissociation must occur from non-equilibrium vibronic levels of the triplet state formed by energy transfer in sensitization or by intersystem crossing in direct photolysis. Thus we find that neither biacetyl nor HFA can cause photodissociation of ketene by energy transfer, yet benzene, with ET = 85 kcal/mol, and mercury, with ET = 1 13 kcal/mol, both sensitize the dissociation of ketene (9,10 …”

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confidence: 70%

The Triplet State of Ketene

McIntosh¹,

Porter²

1972

Can. J. Chem.

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Ketene quenches the phosphorescence of both biacetyl and hexafluoroacetone. Although the quenching of hexafluoroacetone emission is nearly collision-controlled, that of biacetyl is much less efficient. The large difference in the rate constants is attributed to endothermic energy transfer from triplet biacetyl to ketene and exothermic energy transfer from triplet HFA to ketene. From the endothermicity, the lowest triplet state of ketene is estimated to be at 61 k I kcal/mol above its ground state. No sensitized photodecomposition of ketene occurs as a result of energy transfer from either biacetyl or hexafluoroacetone.Le ctttne arr&te la phosphorescence du biacttyle et de l'hexafluoroacttone. Bien que l'extinction de I'emission de I'hexafluoroacitone est pratiquement contr6lte par la collision celle du biacttyle est nettement moins efficace. La grande difftrence dans les constantes de vitesse est attribute au transfert d'tnergie endothermique du biacetyle triplet au cetene et au transfert d'tnergie exothermique du HFA triplet au cetbne. A partir de I'endothermicitt, l'ttat triplet le plus bas pour le cttbne est tvalue a 61 k 1 kcal/mol au dessus de son etat fondamental. I1 n'y a pas de photodCcomposition sensibiliske du cCtene resultant du transfert d'tnergie soit du biacktyle soit de I'hexafluoroacttone.Canadian Journal of Chemistry, 50, 2313Chemistry, 50, (1972 It is now well established that both singlet and triplet state methylene radicals are produced in the primary photodissociation of ketene (1-5). The fraction of the methylenes formed in the triplet state increases as the wavelength of irradiation is increased (2) and the primary quantum yield decreases, becoming strongly pressure dependent at 366 nm (6).If the dissociation obeys a spin correlation rule, and there is no reason it should not, the methylenes would arise from the corresponding excited singlet and triplet states of ketene itself (2). However, because no emission has ever been detected from ketene, little is known about the lowest lying singlet and triplet excited states. Dixon and Kirby (7), in a study of the visible and U.V. absorption spectrum of ketene, concluded that two electronic transitions can be seen. They assigned the origin of the triplet state as the observed onset of absorption, at ca. 61 kcal/mol. In a recent reinvestigation, Laufer and Keller (8) disagreed with Dixon and Kirby and suggested that only one transition is observed, the lowest singlet-singlet absorption. They therefore set an upper limit to the singlet state origin as 61 kcal/mol and located the triplet origin at about 55 kcallmol on the basis of a -"normal" singlet-triplet splitting. The decomposition of ketene can be sensitized by the triplet states of mercury (9) and benzene (10). The fraction of the methylenes then formed in the triplet state is large, which implies that the triplet state of ketene has been formed by energy transfer. In an attempt to locate the triplet state of ketene, Grossman, Semeluk, and Unger (1 1) tried to sensitize the emission of biac...

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“…to explain the forination of 3-methylbutene-1 in all cases a i d they claim t h a t the intervention of triplet methylene is not necessary t o explain its appearance as claiined by Frey (10) and Duncan and CvetanoviC (13). I-Iou~ever, the present results prove that the principal source of 3-methylbutene-1 cannot be due to the rearrangement of a highly energetic species a s its percentage yield increases lvith increasing inert gas pressure and the yield is greater with CF,, than with I-Ie.…”

Section: *Tlzere I S Co?zsiderable Scatter I N Tlze Plots For S-~?zetmentioning

confidence: 98%

The Chemistry of Singlet and Triplet Methylene

Bader¹,

Generosa²

1965

Can. J. Chem.

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Results are reported for the photolysis of small, fixed amounts of diazomethane and cisbutene-2 in the presence of increasing pressures of the inert gases He, Ar, Xe, Nz, and CFa.The variation in the percentage yield of the trans-din~ethylcyclopropane a s a function of the inert gas pressure indicates that two basic mechanisms, with opposite dependencies on the inert gas pressure, are responsible for its formation. An initial decrease in the percentage yield of this trans isomer with increasing pressure indicates that a source is an isomerization of energized molecules. These excited molecules result from the addition of methylene in a singlet state t o cis-butene-2. A subsequent rise in t h e yield of t h e trans isomer with further increases in the pressure indicates that another mechanism, one whose rate is increased by a n increase in pressure, must be present. This is attributed to a mechanism involving triplet methylene. ?'he pressure regions for the observation of the singlet or triplet behavior of methylene are thus ltnown and the inodes of formation of the other C6 products may be determined.

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Production and Reactions of Methylene in the Triplet State

Cited by 51 publications

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The structure and energetics of triplet [B, C, F, H2]

The structure and energetics of triplet [B, C, F, H2]

The Triplet State of Ketene

The Chemistry of Singlet and Triplet Methylene

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