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

2012 ◽  
Vol 65 (7) ◽  
pp. 905 ◽  
Author(s):  
Shin Dee Yeoh ◽  
Benjamin L. Harris ◽  
Tristan J. Simons ◽  
Jonathan M. White

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 13C–13C 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.

2005 ◽  
Vol 58 (7) ◽  
pp. 531
Author(s):  
Laura Andrau ◽  
Jonathan M. White

Low-temperature X-ray crystal structures were determined on a range of derivatives of 4-thiacyclohexanol 5a of varying electron demand with a view to finding evidence for a through-bond interaction between the sulfur lone pair and the oxygenated substituent. In contrast to earlier suggestions, plots of C–OR bond distance versus pKa (ROH) showed that any interaction between the sulfur and the OR group is unlikely to be of a through-bond origin. Furthermore, unimolecular solvolysis rate measurements on the nosylate ester derivative 5g showed that the sulfur actually retards the reaction slightly in comparison with the corresponding sulfur-free analogue 6.


2009 ◽  
Vol 62 (12) ◽  
pp. 1695 ◽  
Author(s):  
Jesse Roth-Barton ◽  
Jonathan M. White

Crystal structures of nitrosobenzene cycloadducts 5–7 reveal structural effects consistent with the early stages of the retro Diels–Alder fragmentation. There is a clear differentiation between the structure parameters of cycloadduct 5, which reacts by a concerted synchronous pathway and that of cycloadduct 6, which must react by a two-step pathway. Based on these data, cycloadduct 7 is predicted to react by a highly asynchronous or two-step pathway.


2008 ◽  
Vol 61 (12) ◽  
pp. 956 ◽  
Author(s):  
Wesley Jackson ◽  
Jonathan M. White

Application of the variable oxygen probe to the polycyclic alcohol 11 and its crystalline ester and ether derivatives provides evidence for a weak interaction between the neighbouring homo-allylic π-system and the C–OR bond; there is no evidence for interaction with the remote π-system. Analysis of the carbon–carbon bond distances in 11–14 reveals structural effects consistent with the manifestation of one of the two possible retro-Diels–Alder reactions in the ground state.


2009 ◽  
Vol 62 (5) ◽  
pp. 419 ◽  
Author(s):  
Yit W. Goh ◽  
Jonathan M. White

Crystal structures of some Diels–Alder cycloadducts of anthracene and a variety of dienophiles reveal structural effects consistent with the manifestation of the early stages of the retro Diels–Alder reaction in the ground state structure. The symmetrical cycloadducts 3 and 4 reveal a qualitative relationship between structure and reactivity, whereas the cycloadducts of 9-methoxyanthracene show structural effects suggestive of the early stages of an asynchronous retro Diels–Alder reaction.


2019 ◽  
Author(s):  
Praveen Gunawardene ◽  
Wilson Luo ◽  
Alexander M. Polgar ◽  
John F. Corrigan ◽  
Mark Workentin

<div> <div> <p>Highly accelerated inverse-electron-demand strain-promoted alkyne-nitrone cycloaddition (IED SPANC) between a sta- ble cyclooctyne (bicyclo[6.1.0]nonyne (BCN)) and nitrones delocalized into a Cα-pyridinium functionality is reported, with the most electron-deficient “pyridinium-nitrone” displaying among the most rapid cycloadditions to BCN that is currently reported. Density functional theory (DFT) and X-ray crystallography are explored to rationalize the effects of N- and Cα-substituent modifications at the nitrone on IED SPANC reaction kinetics and the overall rapid reactivity of pyridinium-delocalized nitrones.</p> </div> </div>


2020 ◽  
Vol 24 (10) ◽  
pp. 1139-1147
Author(s):  
Yang Mingyan ◽  
Wang Daoquan ◽  
Wang Mingan

2-Phenylcyclododecanone and 2-cyclohexylcyclododecanone derivatives were synthesized and characterized by 1H NMR, 13C NMR, HR-ESI-MS and X-ray diffraction. Their preferred conformations were analyzed by the coupling constants in the 1H NMR spectra and X-ray diffraction, which showed the skeleton ring of these derivatives containing [3333]-2-one conformation, and the phenyl groups were located at the side-exo position of [3333]-2-one conformation due to the strong π-π repulsive interaction between the π- electron of benzene ring and π-electron of carbonyl group. The cyclohexyl groups were located at the corner-syn or the side-exo position of [3333]-2-one conformation depending on the hindrance of the other substituted groups. The π-π electron effect played a crucial role in efficiently controlling the preferred conformation of 2-aromatic cyclododecanone and the other 2-aromatic macrocyclic derivatives with the similar preferred square and rectangular conformations.


Molbank ◽  
10.3390/m1200 ◽  
2021 ◽  
Vol 2021 (2) ◽  
pp. M1200
Author(s):  
R. Alan Aitken ◽  
Dheirya K. Sonecha ◽  
Alexandra M. Z. Slawin

The X-ray structure of the title compound has been determined for the first time. Data on its 1H–13C-NMR coupling constants and 15N-NMR spectrum are also given.


2021 ◽  
Vol 103 (2) ◽  
Author(s):  
R. C. Shah ◽  
S. X. Hu ◽  
I. V. Igumenshchev ◽  
J. Baltazar ◽  
D. Cao ◽  
...  

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Longfei Lin ◽  
Mengtian Fan ◽  
Alena M. Sheveleva ◽  
Xue Han ◽  
Zhimou Tang ◽  
...  

AbstractOptimising the balance between propene selectivity, propene/ethene ratio and catalytic stability and unravelling the explicit mechanism on formation of the first carbon–carbon bond are challenging goals of great importance in state-of-the-art methanol-to-olefin (MTO) research. We report a strategy to finely control the nature of active sites within the pores of commercial MFI-zeolites by incorporating tantalum(V) and aluminium(III) centres into the framework. The resultant TaAlS-1 zeolite exhibits simultaneously remarkable propene selectivity (51%), propene/ethene ratio (8.3) and catalytic stability (>50 h) at full methanol conversion. In situ synchrotron X-ray powder diffraction, X-ray absorption spectroscopy and inelastic neutron scattering coupled with DFT calculations reveal that the first carbon–carbon bond is formed between an activated methanol molecule and a trimethyloxonium intermediate. The unprecedented cooperativity between tantalum(V) and Brønsted acid sites creates an optimal microenvironment for efficient conversion of methanol and thus greatly promotes the application of zeolites in the sustainable manufacturing of light olefins.


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