Isotopic perturbation of a degenerate valence isomerization. A <sup>13</sup>C NMR study of deuterio‐1,5‐dimethylsemibullvalene

Askani, R.; Kalinowski, H.‐O.; Weuste, Burkhard

doi:10.1002/mrc.1270180313

Cited by 23 publications

(8 citation statements)

References 6 publications

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“…The energy difference between the isotopomers d 2 ‐ 8 and d 4 ‐ 8 was determined by Askani et al. to be Δ G ( T )=−0.12 + 0.00018 T kcal mol −1 , and is in good agreement with the Δ E =−0.09 kcal mol −1 calculated at the B3LYP/6‐311G(d,p) level of theory. Several DFT and ab initio methods were used to calculate the energy difference, however, as expected, the calculations are quite robust with only small variations in energy (see Table S1).…”

Section: Methodssupporting

confidence: 76%

“…Relative energies are given in kcal mol −1 (values within parentheses given in cm −1 ), with experimental values for E a having been reported by Moskau et al . and Δ G by Askani et al . The value of 17.3 kcal mol −1 corresponds to the energy of a photon with 6064 cm −1 .…”

Section: Methodsmentioning

confidence: 95%

“…Borden et al. recommended that their prediction be tested with the 1,5‐dimethylsemibullvalenes d 2 ‐ 8 and d 4 ‐ 8 , which are readily available by a synthesis described by Askani et al . With 4.8 kcal mol −1 the barrier for the Cope rearrangement in 8 is slightly smaller than that in the parent semibullvalene …”

Section: Methodsmentioning

confidence: 99%

“…[a] Predicted isotopomeric ratios as derived by Boltzmann distribution using the experimental energy difference, and calculated ZPVE difference between the isotopomers (Note: ratio in p‐ H 2 experiments could not be evaluated reliably). [b] Performed using a filter with a cutoff of >1000 cm −1 (in contrast to all other experiments using a filter with a cutoff of >2000 cm −1 ).…”

Section: Methodsmentioning

confidence: 99%

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The Cope Rearrangement of 1,5‐Dimethylsemibullvalene‐2(4)‐d₁: Experimental Evidence for Heavy‐Atom Tunneling

et al. 2017

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As an experimental test of the theoretical prediction that heavy‐atom tunneling is involved in the degenerate Cope rearrangement of semibullvalenes at cryogenic temperatures, monodeuterated 1,5‐dimethylsemibullvalene isotopomers were prepared and investigated by IR spectroscopy using the matrix isolation technique. As predicted, the less thermodynamically stable isotopomer rearranges at cryogenic temperatures in the dark to the more stable one, while broadband IR irradiation above 2000 cm−1 results in an equilibration of the isotopomeric ratio. Since this reaction proceeds with a rate constant in the order of 10−4 s−1 despite an experimental barrier of Ea=4.8 kcal mol−1 and with only a shallow temperature dependence, the results are interpreted in terms of heavy‐atom tunneling.

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Section: Methodssupporting

confidence: 76%

Section: Methodsmentioning

confidence: 95%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

See 2 more Smart Citations

The Cope Rearrangement of 1,5‐Dimethylsemibullvalene‐2(4)‐d₁: Experimental Evidence for Heavy‐Atom Tunneling

et al. 2017

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Section: Methodsmentioning

confidence: 99%

The Cope Rearrangement of 1,5‐Dimethylsemibullvalene‐2(4)‐d₁: Experimental Evidence for Heavy‐Atom Tunneling

et al. 2017

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As an experimental test of the theoretical prediction that heavy-atom tunneling is involved in the degenerate Cope rearrangement of semibullvalenes at cryogenic temperatures, monodeuterated 1,5-dimethylsemibullvalene isotopomers were prepared and investigated by IR spectroscopy using the matrix isolation technique. As predicted, the less thermodynamically stable isotopomer rearranges at cryogenic temperatures in the dark to the more stable one, while broadband IR irradiation above 2000 cm results in an equilibration of the isotopomeric ratio. Since this reaction proceeds with a rate constant in the order of 10 s despite an experimental barrier of E =4.8 kcal mol and with only a shallow temperature dependence, the results are interpreted in terms of heavy-atom tunneling.

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Struktur von 1,5‐Dimethylsemibullvalen‐3,7‐dicarbonsäure‐dimethylester und 1,5‐Dimethylsemibullvalen‐3,7‐dicarbonitril

et al. 1983

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Eine Eintopfsynthese des Semibullvalendiesters 3a und seine Uberfuhrung in das Dinitril3e werden beschrieben. Die Rontgenstrukturanalyse zeigt fur den Semibullvalendiester 3a normale Bindungsabstande fur C2 -C8 und C4 -C6. Dagegen weist das Dinitril 3e im festen Zustand eine sehr lange C2-C8-Bindung und einen kurzen C4-C6-Abstand auf.Structure of Dimethyl 1,5-Dimethylsemibullvalene-3,7-dicarboxylate and 1,5-Dimethylsemibullvalene-3,7-dicarbonitrile A one-pot synthesis for semibullvalene diester 3a and its transformation to dinitrile 3e are reported. X-ray analysis shows normal distances C2-C8 and C4-C6 for semibullvalene diester 3a; on the contrary, for the dinitrile 3e an unusual long C2 -C8 bond and a short C4 -C6 distance are found in the solid state.Semibullvalene gehen eine sehr leichte Cope-Umlagerung ein; die Aktivierungsenergien gehoren mit zu den kleinsten, welche fur sigmatrope Reaktionen gefunden wurden. Hiickel-Rechnungen ') und MINDO-ZBerechnungen ' ) zeigen Aktivierungsschwellen, also ubergangszustande fur die Cope-Umlagerung der Semibullvalene an; Elektronendonatoren in Positionen 1 und 5 sowie Elektronenakzeptoren in Stellung 2,4,6 und 8 sollen nach diesen Rechnungen die Aktivierungsschwellen weiter senken und moglicherweise eine bishomoaromatische Struktur ermoglichen, die sich in gleichen Bindungsabstanden C2 -C8 und C4 -C6 zu erkennen geben sollte.Eine groRe Zahl von Publikationen auf dem Gebiet der Semib~llvalene~) zeigt das andauernde Interesse an dieser Verbindungsklasse, insbesondere den Versuch, zu einem Vertreter mit bishomoaromatischer Struktur durchzustoRen. Da wir vor kurzem eine variationsfahige Eintopf-Synthese zur Darstellung der Semibullvalene auffinden konnten4), deren Mechanismus sich klaren lien '), haben wir fur zwei ausgewahlte Vertreter mit Hilfe der Rdntgenstrukturanalyse Bindungsabstande und Bindungswinkel bestimmt. Synthese von 3a und 3eDie Umsetzung von Tetrazindiester l a mit dem Bi-2-cyclopropen-1-y1 2 verlauft selbst bei Raumtemperatur sturmisch unter N,-Entwicklung; in ca. 70proz. Ausbeute

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Isotopic perturbation of a degenerate valence isomerization. A ¹³C NMR study of deuterio‐1,5‐dimethylsemibullvalene

Cited by 23 publications

References 6 publications

The Cope Rearrangement of 1,5‐Dimethylsemibullvalene‐2(4)‐d₁: Experimental Evidence for Heavy‐Atom Tunneling

The Cope Rearrangement of 1,5‐Dimethylsemibullvalene‐2(4)‐d₁: Experimental Evidence for Heavy‐Atom Tunneling

The Cope Rearrangement of 1,5‐Dimethylsemibullvalene‐2(4)‐d₁: Experimental Evidence for Heavy‐Atom Tunneling

Struktur von 1,5‐Dimethylsemibullvalen‐3,7‐dicarbonsäure‐dimethylester und 1,5‐Dimethylsemibullvalen‐3,7‐dicarbonitril

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Isotopic perturbation of a degenerate valence isomerization. A 13C NMR study of deuterio‐1,5‐dimethylsemibullvalene

Cited by 23 publications

References 6 publications

The Cope Rearrangement of 1,5‐Dimethylsemibullvalene‐2(4)‐d1: Experimental Evidence for Heavy‐Atom Tunneling

The Cope Rearrangement of 1,5‐Dimethylsemibullvalene‐2(4)‐d1: Experimental Evidence for Heavy‐Atom Tunneling

The Cope Rearrangement of 1,5‐Dimethylsemibullvalene‐2(4)‐d1: Experimental Evidence for Heavy‐Atom Tunneling

Struktur von 1,5‐Dimethylsemibullvalen‐3,7‐dicarbonsäure‐dimethylester und 1,5‐Dimethylsemibullvalen‐3,7‐dicarbonitril

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Isotopic perturbation of a degenerate valence isomerization. A ¹³C NMR study of deuterio‐1,5‐dimethylsemibullvalene

The Cope Rearrangement of 1,5‐Dimethylsemibullvalene‐2(4)‐d₁: Experimental Evidence for Heavy‐Atom Tunneling

The Cope Rearrangement of 1,5‐Dimethylsemibullvalene‐2(4)‐d₁: Experimental Evidence for Heavy‐Atom Tunneling

The Cope Rearrangement of 1,5‐Dimethylsemibullvalene‐2(4)‐d₁: Experimental Evidence for Heavy‐Atom Tunneling