Extension of Saunders' Isotopic Perturbation Method as Probe for the Structures in Solution of 2,4,6,8-Substituted Barbaralanes – NMR-Spectroscopic Evidence for the Coexistence of Localised and Delocalised States[1]

Quast, Helmut; Seefelder, Maximilian; Becker, Christian F. W.; Heubes, Markus; Peters, E.‐M.; Peters, Karl

doi:10.1002/(sici)1099-0690(199911)1999:11<2763::aid-ejoc2763>3.0.co;2-4

Cited by 19 publications

(14 citation statements)

References 35 publications

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“…In 11a the barrier height was found to decrease from Δ H ‡ =1.9 kcal/mol in cyclohexane to Δ H ‡ =0.8 kcal/mol in butyronitrile. Quast's experiments indicated 10e and 12a to be the dominant species present in N,N′‐dimethylpropylene urea 15, 16.

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Section: Introductionsupporting

confidence: 62%

B3LYP calculations on bishomoaromaticity in substituted semibullvalenes*

et al. 2001

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B3LYP/6‐31G* calculations on the degenerate rearrangements of substituted semibullvalenes spuriously predict the relative enthalpies of the bishomoaromatic TSs to be lower than the experimental values. However, the calculations do make the useful and experimentally testable prediction that the two cyano and two phenyl substituents in 2,6‐dicyano‐4,8‐diphenylsemibullvalene (9d) are more likely than four cyano substituents in 2,4,6,8‐tetracyanosemibullvalene (9f) or the four phenyl substituents in 2,4,6,8‐tetraphenylsemibullvalene (9g) to produce a semibullvalene that has a bishomoaromatic equilibrium geometry in the gas phase. The major reason for the surprising finding that 9d is more likely to be bishomoaromatic than 9g is shown to be steric interactions between the phenyl groups at C‐2 and C‐8 and at C‐4 and C‐6 in bishomoaromatic structure 10g. These interactions inhibit the conjugative stabilization of 10g; but they are absent in bishomoaromatic structure 10d, where cyano groups replace the phenyl groups at C‐2 and C‐6 in 10g. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1565–1573, 2001

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…”

Section: Introductionsupporting

confidence: 62%

B3LYP calculations on bishomoaromaticity in substituted semibullvalenes*

et al. 2001

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“…Recently, Quast et al [70] have proposed an extension of Saunders isotopic perturbation method for studying valence tautomerism in substituted barbaralenes, where a small fraction of the delocalised form co-exist with the localised valence tautomers.…”

Section: Deuterium Perturbation Of Equilibriummentioning

confidence: 99%

“…The Saunders method of isotopically perturbed equilibrium has been shown to be a useful tool for studying the structure of compounds that undergo degenerate sigmatropic rearrangements [70,98]. Recently, Johnston et al [98] reinvestigated the degenerate Cope rearrangement of barbaralone.…”

Section: Structure Studies Conformational Analysis and Valence Tautomentioning

confidence: 99%

Studies based on deuterium isotope effect on 13C chemical shifts

Dziembowska

Hansen

Rozwadowski

2004

Progress in Nuclear Magnetic Resonance Spectroscopy

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“…Quast, Seefelder and co-workers further explore this unusual solvent effect by NMR using Saunders' isotopic perturbation method. 69 Quast and co-workers have studied the thermal rearrangement reactions of substituted semibullvalenes to form cyclooctatetraenes. 70 They conclude that the same factors which stabilize the transition state for Cope rearrangement also promote rearrangement to form cyclooctatetraenes.…”

Section: Cope Rearrangementsmentioning

confidence: 99%