Mechanistic studies on the Wolff rearrangement: the chemistry and spectroscopy of some .alpha.-keto carbenes

McMahon, Robert J.; Chapman, O. L.; Hayes, R. Andrew; Heß, Thomas; Krimmer, Hans Peter

doi:10.1021/ja00311a063

Cited by 103 publications

(96 citation statements)

References 3 publications

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“…To expand our research on transient species, we used this instrument to study the vacuum pyrolysis of 4-diazoisothiochroman-3-one (la). We anticipated that this study would add new information to the limited amount of data that are available on the vacuum pyrolysis of a-diazocarbonyl compounds in contrast to the large body of work that has been accumulated on the photochemistry of this class of compounds (4)(5)(6)(7)(8)(9)(10). Our goals were to compare the chemistries of l a and l b and establish whether two new transients, thiaketene 3a and benzocyclobutenthione (6a), that are potential products of the pyrolysis of l a could be characterized with pes.…”

Section: Methodsmentioning

confidence: 99%

A study of the vacuum pyrolysis of 4-diazoisothiochroman-3-one with Hel ultraviolet photoelectron spectroscopy

Ma¹,

Roy²,

Kresge³

et al. 1996

Can. J. Chem.

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A newly developed ultraviolet photoelectron spectrometer apparatus that utilizes a tunable 50 W CW CO:, laser as a directed heat source is used to study the vacuum pyrolysis of 4-diazoisothiochroman-3-one (la). Analysis of the pyrolysate with ultraviolet photoelectron spectroscopy shows that l a undergoes a facile pyrolysis at a laser power level of less than 26 W, yielding two new compounds: thiaketene 3a, the product of a Wolff rearrangement, and benzocyclobutenthione (6a), which can be derived from thiacarbene 4a, the decarbonylation product of 3a. Activation enthalpieslenergies calculated at the AM 1 and ab initio levels of theory indicate that, unlike the case of 4-diazoisochroman-3-one (lb), the Wolff rearrangement of the incipient carbene may be concerted with loss of nitrogen from l a . The activation enthalpylenergy calculated for the decarbonylation of 3a is significantly higher (AM1,20.5 kcallmol; RHFl6-3 lG(d), 11.7 kcallmol; MP2(full)llRHFl6-31G(d), 14.3 kcallmol) than the activation enthalpylenergy for the decarbonylation of 3b. This result is in keeping with the fact that we detect 3a, but 3b is not found in detectable amounts in the pyrolysate of lb.Key words: vacuum pyrolysis, 4-diazoisothiochroman-3-one, He1 ultraviolet photoelectron spectroscopy, AM1 and ab initio calculations.Resume : On a utilist un spectromktre de photoCmission de photoklectrons dans l'ultraviolet rkcemment mis au point qui utilise un laser ajustable au CO1 de 50 W CW comme source dirigCe de chaleur, pour Ctudier la pyrolyse sous vide de la 4-diazoisothiochroman-3-one (la). L'analyse du pyrolysat par la spectroscopie de photoCmission de photoClectrons dans l'ultraviolet montre que le composC l a subit facilement la pyrolyse i un niveau de puissance du laser infkrieure i 26 W pour donner deux nouveaux composCs : la thiacCt2ne 3a, le produit d'un rearrangement de Wolff, et la benzocyclobutenthione (6a) qui peut provenir du thiacarbkne 4a, le produit de dCcarbonylation du produit 3a. Les Cnergieslenthalpies d'activation calculCes aux niveaux thkoriques AM1 et ab initio indiquent que, contrairement au cas de la 4-diazoisochroman-3-one (lb), la transposition de Wolff du carbkne naissant peut-&tre concertCe avec la perte d'azote i partir de la. L'tnergielenthalpie d'activation calculte pour la dCcarbonylation de 3a est de f a~o n significative plus ClevCe (AM1,20,5 kcallmol; RHFl6-31G(d), 11,7 kcallmol; MP2(complet)llRHFl6-3 lG(d), 14,3 kcallmol) que 1'Cnergielenthalpie d'activation pour la dkcarbonylation de 3b. Ce rCsultat est en accord avec le fait que nous avons detect6 le composC 3a mais le compost 3b n'est pas present en quantitks detectables dans le pyrolysat de lb.Mots clPs : pyrolyse sous vide, 4-diazoisothiochroman-3-one, He1 spectroscopie de photoCmission de photoClectrons dans l'ultraviolet, calculs AM1 et ab initio.[Traduit par la rkdaction] I

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Section: Methodsmentioning

confidence: 99%

A study of the vacuum pyrolysis of 4-diazoisothiochroman-3-one with Hel ultraviolet photoelectron spectroscopy

Ma¹,

Roy²,

Kresge³

et al. 1996

Can. J. Chem.

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“…In addition, the interaction between electronic states with different spin multiplicities, such as intersystem crossing (ISC), sometimes plays an important role in the interpretation of carbene reaction mechanisms. 1,2,11 Carbenes containing conjugated rings are of interest 3-10 because their molecular and electronic structures are very sensitive to the interaction between nonbonding electrons and the π system. Indeed, this interaction plays a role in characterizing the nature of low-lying electronic states.…”

Section: Introductionmentioning

confidence: 99%

Theoretical Study of Oxocyclohexadienylidene Isomers: Electronic Structures and Molecular Properties

et al. 2000

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The molecular properties and electronic structures for three isomers of oxocyclohexadienylidene were investigated using multiconfiguration SCF (MCSCF) wave functions. The ground electronic states of the ortho and para isomers are the open shell triplet, whereas the meta isomer has a singlet ground state with significant open shell character. The structural features of the ground states of all three isomers are close to the quinoid type structure. Several molecular properties such as the electron spin density, electron affinity (EA), acidity and bond dissociation energy for the three isomers and/or their corresponding radicals are also considered and are compared with experimental values. In particular, the MCSCF(8,8)/6-31+G* electron spin densities for both ortho and para isomers are very close to the experimental values of the phenoxyl radical. Disciplines Chemistry CommentsReprinted (adapted) with permission from

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“…The C-N=N-C dihedral angles of triplet DBH and DBO are predicted to be about 28.0 and 40. 4 o at the UB3LYP/6-31G(d) level of theory, respectively. These values somewhat decrease in their fused ring derivatives.…”

Section: Resultsmentioning

confidence: 99%

“…[1][2][3][4] In particular, deazetization (nitrogen loss) of azoalkanes is known to be one of the important routes of formation of photochemically active azo radicals and diradicals. [5][6][7][8] Extensive studies for verifying the mechanisms of such reactions have been reported.…”

Section: Introductionmentioning

confidence: 99%

“…[5][6][7][8] Extensive studies for verifying the mechanisms of such reactions have been reported. [1][2][3][4][5][6][7][8][9][10][11][12][13] The electronic structure of azo chromophores is also believed to play a key role in determining the reaction mechanism and photochemical properties of many azoalkanes. [5][6][7][8] The relative energies of their ground and excited electronic states appear to be useful in explaining some reaction mechanisms involving azo species.…”

Section: Introductionmentioning

confidence: 99%

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A Theoretical Study of Some Bicyclic Azoalkanes

Chung

Lee²

2006

Bulletin of the Korean Chemical Society

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The molecular structures of the ground and lowest triplet states of 2,3-diazabicyclo[2.2.1]hept-2-ene (DBH), 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) and their fused ring derivatives are investigated with an ab initio method and the density functional theory. Unlike the singlet DBH and DBO, the azo skeletal structures of the triplet counterparts are turned out to be quite sensitive to the change of the electronic structure of the fused ring. The B3LYP C-N=N-C dihedral angles of the triplet DBH and DBO are estimated to be about 28.0 and 40.4 o , respectively. The B3LYP singlet-triplet energy gaps for DBH and DBO are predicted to be 58.4 and 48.4 kcal/ mol, respectively. The triplet state energy can be lowered drastically by the presence of the remote π-π interaction as in the case of 1bb'.

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Mechanistic studies on the Wolff rearrangement: the chemistry and spectroscopy of some .alpha.-keto carbenes

Cited by 103 publications

References 3 publications

A study of the vacuum pyrolysis of 4-diazoisothiochroman-3-one with Hel ultraviolet photoelectron spectroscopy

A study of the vacuum pyrolysis of 4-diazoisothiochroman-3-one with Hel ultraviolet photoelectron spectroscopy

Theoretical Study of Oxocyclohexadienylidene Isomers: Electronic Structures and Molecular Properties

A Theoretical Study of Some Bicyclic Azoalkanes

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