Structure Correlation Study of the Beckmann Rearrangement: X-ray Structural Analysis and 13C-13C 1-Bond Coupling Constant Study of a Range of Cyclohexanone Oxime Derivatives

The X-ray structures of a range of oxime derivatives (1 and 4), of cyclohexanone and 4-tert-butylcyclohexanone, where the electron demand of the oxygenated substituent on the oxime nitrogen (OR) is systematically varied were determined. It was established that as the OR group becomes more electron d...

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Bibliographic Details
Published inAustralian journal of chemistry Vol. 65; no. 7; pp. 905 - 917
Main Authors Yeoh, Shin Dee, Harris, Benjamin L., Simons, Tristan J., White, Jonathan M.
Format Journal Article
LanguageEnglish
Published CLAYTON Csiro Publishing 01.01.2012
Subjects
Chemistry
Chemistry, Multidisciplinary
Physical Sciences
Science & Technology
RING-FLIP PROCESSES
BOND-LENGTH
C-13
CYCLOADDUCTS
CRYSTAL-STRUCTURE
STEREOCHEMISTRY
REACTIVITY
LIGAND
SOLID-STATE
MANIFESTATIONS
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Summary:The X-ray structures of a range of oxime derivatives (1 and 4), of cyclohexanone and 4-tert-butylcyclohexanone, where the electron demand of the oxygenated substituent on the oxime nitrogen (OR) is systematically varied were determined. It was established that as the OR group becomes more electron demanding, then the N-OR bond distance increases, consistent with the early stages of bond breakage. Concomitant with this structural effect was a noticeable closing up of the N1-C1-C2 bond angle, consistent with the early stages of migration of the antiperiplanar carbon onto the nitrogen substituent. These structural effects are consistent with the manifestation of the early stages of the Beckmann rearrangement in the ground state structures of these oxime derivatives. The carbon-carbon bond distances of the participating carbons in this rearrangement, however, did not vary in a systematic way with the electron demand of the OR substituent, suggesting that the structural effects are too small to be detected using X-ray crystallography. However, the C-13-C-13 1-bond coupling constants, which are sensitive to the effects of hyperconjugation, were shown to vary in a systematic way with the electron demand of the OR substituent. Structural effects in the oxime 5 derivatives of 2,2-dimethylcyclohexanone, a substrate that is prone to Beckmann fragmentation rather than Beckmann rearrangement, were similar but smaller in magnitude.
ISSN:0004-9425
1445-0038
DOI:10.1071/CH12079