ESR Observation of Thermally Produced Triplet Nitrenes and Photochemically Produced Triplet Cycloheptatrienylidenes

Kuzaj, Martin; Lüerssen, Holger; Wentrup, Curt

doi:10.1002/anie.198604801

Cited by 85 publications

(121 citation statements)

References 15 publications

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“…There is a reversal of energy ordering at the G2(RMP2,SVP)//QCI (E e ) level, 54 with 3 A 2 preferred by 2 kJ mol -1 . This result is in agreement with recent CASPT2N calculations of Schreiner et al 40 The prediction of a stable triplet state of 3 is in agreement with the observation of cycloheptatrienylidene by ESR spectroscopy, 21 although current calculations do not permit a clear conclusion as to which state is being observed. Since the singlet 1 A 2 state is calculated to lie lower in energy than the closely related 3 A 2 state, 39,40 the 3 A 2 carbene may be expected to easily (53) Schlegel, H. B. J. Chem.…”

Section: Discussionsupporting

confidence: 93%

Interconversions of Phenylcarbene, Cycloheptatetraene, Fulvenallene, and Benzocyclopropene. A Theoretical Study of the C₇H₆ Energy Surface

1996

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Ab initio calculations at the G2(MP2,SVP) and B-LYP/6-311+G(3df,2p)+ZPVE levels have been used to examine the potential energy surface of C(7)H(6). Fulvenallene (6) is the most stable C(7)H(6) isomer considered in this study. 1-Ethynylcyclopentadiene (9A), benzocyclopropene (10), and 1,2,4,6-cycloheptatetraene (4) lie 12, 29, and 49 kJ mol(-)(1), respectively, above 6. Phenylcarbene (1) is calculated is to have a triplet ((3)A") ground state, 16 kJ mol(-)(1) more stable than the singlet state ((1)A'). Interconversion of 1 and 4 is predicted to have a moderate activation barrier, with the involvement of a stable bicyclic intermediate (bicyclo[4.1.0]hepta-2,4,6-triene, 2). However, 2 is found to lie in a shallow potential energy well with a small barrier (8 kJ mol(-)(1)) to rearrangement to 4. At the G2(RMP2,SVP)//QCI level, the (3)A(2) and (3)B(1) triplet states of cycloheptatrienylidene ((3)3) are predicted to lie very close in energy. The singlet "aromatic" cycloheptatrienylidene ((1)3, (1)A(1)) is found to be a transition structure interconverting two chiral cyclic allenes (4) and it lies approximately 25 kJ mol(-)(1) below the triplet states. Bicyclo[3.2.0]hepta-1,3,6-triene (5) is predicted to be a stable equilibrium structure, lying in a significant energy well. Rearrangement of 4 to 5 constitutes the rate-determining step for the rearrangement of phenylcarbene to fulvenallene (6), the ethynylcyclopentadienes (9), and spiro[2.4]heptatriene (7). Rearrangement of 9A to 6, via a 1,4-H shift, requires a large barrier of 325 kJ mol(-)(1). Rearrangement of benzocyclopropene (10) to 6 involves a methylenecyclohexadienylidene intermediate (27) and is associated with an energy barrier of 223 kJ mol(-)(1). The calculated mechanisms and energetics for the interconversions of various C(7)H(6) isomers are in good accord with experimental results to date.

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Section: Discussionsupporting

confidence: 93%

Interconversions of Phenylcarbene, Cycloheptatetraene, Fulvenallene, and Benzocyclopropene. A Theoretical Study of the C₇H₆ Energy Surface

1996

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“…[180] Mehrere andere,schwingungsmäßig kalte freie Radikale wurden durch Pulspyrolyse erhalten, [181] einschließlich des Methylradikals. [184,185] Cyclopropenyliden (94), Propadienyliden (95)u nd Propargylen (96) wurden durch Pulspyrolyse von 3-Chlorcyclopropen, 1,3-Dibrompropin bzw.3-Diazopropin erhalten [Gleichungen (46)- (48)] und durch ihre Massen-und Photoelektronenspektren charakterisiert. [183] Alkylradikale,d ie durch gepulste Pyrolyse entstanden waren, sind durch Photoionisierung mit Femtosekundenauflçsunganalysiert worden.…”

Section: Gepulste Pyrolyse (Strahlexpansions-fvp)unclassified

“…(23)]. [96] Analog wurden die EPR-Spektren vieler anderer Aryl-und Heteroarylnitrene beobachtet (Naphthyl-, Phenanthryl-, Pyridyl-, Pyrimidinyl-, Pyrazinyl-, 3-Pyridazinylnitrene und so weiter). [58] Die gleiche Methode bei ähnlicher Apparatur wurde auch eingesetzt, um das IR-Spektrum von Phenylnitren in Ar-Matrix zu erhalten.…”

Section: Epr- Ir-und Uv/vis-spektroskopieunclassified

“…[183] Alkylradikale,d ie durch gepulste Pyrolyse entstanden waren, sind durch Photoionisierung mit Femtosekundenauflçsunganalysiert worden. [184,185] Cyclopropenyliden (94), Propadienyliden (95)u nd Propargylen (96) wurden durch Pulspyrolyse von 3-Chlorcyclopropen, 1,3-Dibrompropin bzw.3-Diazopropin erhalten [Gleichungen (46)-(48)] und durch ihre Massen-und Photoelektronenspektren charakterisiert. [180] Cyclopropenyliden wurde ebenfalls durch konventionelle FVP von Perester-u nd Spirocycloalken-Vorstufen generiert und IR-spektroskopisch in Ar-Matrix identifiziert;d ort konnte auch gezeigt werden, dass es photochemisch mit Propadienyliden und Propargylen im Austausch steht.…”

Section: Gepulste Pyrolyse (Strahlexpansions-fvp)unclassified

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Flash‐Vakuumpyrolyse – Techniken und Reaktionen

Wentrup

2017

Angewandte Chemie

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Die Anfänge der Flash‐Vakuumpyrolyse (FVP) ergaben sich in den 1940er und 1950er Jahren hauptsächlich aus dem massenspektrometrischen Nachweis pyrolytisch entstandener freier Radikale. In den 1960er Jahren begannen Organiker mit der Durchführung von FVP‐Experimenten zum Zweck der Isolierung neuer und interessanter Verbindungen und zum Verständnis pyrolytischer Prozesse. Seitdem wurden viele unterschiedliche Typen von Apparaten und Techniken entwickelt. Zielsetzung dieses Aufsatzes ist es, die wichtigsten Methoden vorzustellen wie auch eine Übersicht über typische Reaktionen und Beobachtungen zu geben, die mit den verschiedenen Techniken erreicht werden können. Dies umfasst unter anderem präparative FVP, chemische Abfangreaktionen, Matrixisolierung sowie Tieftemperatur‐Spektroskopie reaktiver Intermediate und instabiler Moleküle. Darüber hinaus ist die Kombination von FVP mit Matrixisolierung und Photochemie ein wirkungsvolles Instrument für Untersuchungen von Reaktionsmechanismen.

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“…Carbene T-4 could be independently synthesized and characterized by matrix EPR spectroscopy. [8] According to calculations at the CCSD(T) level of theory, allene 2 is about 13 kcal/mol more stable than carbene T-1, and carbene T-4 lies more than 25 kcal/mol above 2. [9] In this study, the earlier assignment of the IR spectra of 1 and 2 was confirmed.…”

Section: Introductionmentioning

confidence: 99%

1‐Phenyl‐1,2,4,6‐cycloheptatetraene: the missing intermediate of the diphenylcarbene to fluorene rearrangement

Costa

Sander

2014

J of Physical Organic Chem

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The photochemistry of diphenylcarbene 5, matrix-isolated in argon at 3-5 K was investigated by UV-Vis, IR, and EPR spectroscopy. Although carbene 5 proved to be stable toward broadband UV irradiation, it slowly rearranges to 1-phenyl-1,2,4,6-cycloheptatetraene 8 during irradiation with the intense light of a 445-nm diode laser. Other intermediates were not observed. Allene 8 is the key intermediate that was missing in the proposed mechanism of the rearrangement of 5 to f luorene 7.

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ESR Observation of Thermally Produced Triplet Nitrenes and Photochemically Produced Triplet Cycloheptatrienylidenes

Cited by 85 publications

References 15 publications

Interconversions of Phenylcarbene, Cycloheptatetraene, Fulvenallene, and Benzocyclopropene. A Theoretical Study of the C₇H₆ Energy Surface

Interconversions of Phenylcarbene, Cycloheptatetraene, Fulvenallene, and Benzocyclopropene. A Theoretical Study of the C₇H₆ Energy Surface

Flash‐Vakuumpyrolyse – Techniken und Reaktionen

1‐Phenyl‐1,2,4,6‐cycloheptatetraene: the missing intermediate of the diphenylcarbene to fluorene rearrangement

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ESR Observation of Thermally Produced Triplet Nitrenes and Photochemically Produced Triplet Cycloheptatrienylidenes

Cited by 85 publications

References 15 publications

Interconversions of Phenylcarbene, Cycloheptatetraene, Fulvenallene, and Benzocyclopropene. A Theoretical Study of the C7H6 Energy Surface

Interconversions of Phenylcarbene, Cycloheptatetraene, Fulvenallene, and Benzocyclopropene. A Theoretical Study of the C7H6 Energy Surface

Flash‐Vakuumpyrolyse – Techniken und Reaktionen

1‐Phenyl‐1,2,4,6‐cycloheptatetraene: the missing intermediate of the diphenylcarbene to fluorene rearrangement

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Interconversions of Phenylcarbene, Cycloheptatetraene, Fulvenallene, and Benzocyclopropene. A Theoretical Study of the C₇H₆ Energy Surface

Interconversions of Phenylcarbene, Cycloheptatetraene, Fulvenallene, and Benzocyclopropene. A Theoretical Study of the C₇H₆ Energy Surface