Alcoxy-2, aryloxy-2, acyloxy-2 cyclohexanones. Synthèse et étude de leur équilibre conformationnel

Cantacuzène, D.; Tordeux, Marc

doi:10.1139/v76-390

Cited by 20 publications

(11 citation statements)

References 7 publications

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“…Deuterochloroform (99.96%) and acetone-d6 (99.9%) were obtained from Merck, Sharp and Dohme. Acetonitrile (99.5%) was Evidence in support of such a steric effect has been reported in 2-alkoxycyclohexanones (8), where the percent of axial conformation was found to increase with the size of the alkoxy group.…”

Section: Methodsmentioning

confidence: 55%

“…Previous determinations of the conformational equilibrium [ l ] for cyclohexanones by 'Hmr measurements relied upon either the chemical shift parameter (4) or the spin-spin splitting of the methine proton at C2 (4,8). The latter method used the magnitude of the half bandwidth relative to that observed in model compounds to assess the proportion of equatorial conformer.…”

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confidence: 99%

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On the purported axial preference in 2-methylthio and 2-methoxycyclohex-anones: steric effects versus orbital interactions

Fraser¹,

Faibish²

1995

Can. J. Chem.

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Abstract:The value for the equilibrium constant representing the ratio of equatorial to axial conformers for 2-methylthio-and 2-methoxycyclohexanone has been measured in five solvents using 500 MHz 'H nuclear magnetic resonance. In cyclohexane solvent, the methylthio group is found to have a large axial preference while that for the methoxy is negligible. For both compounds the equilibrium shows a strong solvent dependence.Comparison of these results with those known for the halo derivatives shows the amount of axial to increase in the order: fluoro, methoxy, chloro, bromo, and methylthio. With the aid of molecular mechanics calculations it is concluded that the order of conformational preference can be attributed to a variation in the van der Waals interaction between the substituent and the carbonyl group in the equatorial conformer.Key words: a-substituted cyclohexanones, conformation, MMX calculations, steric and dipolar effects.Resume : Utilisant la rksonance magnCtique nuclCaire du 'H a 500 MHz et opCrant dans cinq solvants, on a mesurC la valeur de la constante d'tquilibre reprksentant le rapport des conformkres Cquatorial et axial des 2-mCthylthio-et 2-mCthoxycyclohexanones. Dans le cyclohexane comme solvant, on trouve que le groupe mtthylthio a une prCfCrence axiale alors que celle du groupe mCthoxy est negligeable. Pour les deux composts, 1'Cquilibre depend fortement du solvant. Une comparaison de ces rCsultats avec ceux connus pour les dCrivCs halogCnCs montre que la quantitC de conformkre axial augrnente dans l'ordre : fluoro, mCthoxy, chloro, bromo et rntthylthio. En se basant sur des calculs de mCcanique molCculaire, on conclut que l'ordre de prCftrences conformationnelles peut Etre attribuC a une variation de l'interaction de van der Waals entre le substituant et le groupe carbonyle du conformkre Cquatorial.

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Section: Methodsmentioning

confidence: 55%

mentioning

confidence: 99%

On the purported axial preference in 2-methylthio and 2-methoxycyclohex-anones: steric effects versus orbital interactions

Fraser¹,

Faibish²

1995

Can. J. Chem.

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“…Thus, energetically, there is no strong conformational bias in the equilibria of A and B. Fractional crystallization had also afforded separate diastereomers whose X-ray crystal structures were determined (13) 5 . It became clear that isomer A was the RS isomer and B was the RR isomer.…”

Section: Resultsmentioning

confidence: 99%

“…However, the possibility of the role of σ C-X → π C O = * and n X → π C O = * stabilizing orbital interactions as contributors to the conformational preferences was also recognized ( Fig. 1) (5,6).…”

Section: Introductionmentioning

confidence: 99%

Ab initio DFT calculations of the configurational and conformational preferences of 2-phenylsulfinylcyclohexanones Evidence for "exo-anomeric" interactions

Trapp¹,

Wojcik²,

Zajac³

et al. 2006

Can. J. Chem.

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The conformational analysis of 2-phenylsulfinylcyclohexanone by ab initio density functional calculations is described. Six conformations corresponding to axial/equatorial isomers and rotation about the exocyclic C2-S bond in each of the RR or RS diastereomers were calculated and the results were examined in terms of relative energies, electrostatic interactions, orbital interactions, and geometrical variations. The global minimum conformation was the RS isomer that positioned the phenylsulfinyl moiety in an equatorial orientation and the sulfinyl oxygen in an anti orientation with respect to the carbonyl carbon atom. Of the other three low energy conformations, only one had a gauche arrangement of these atoms, and only in one of the four lower energy conformations was evidence found for a S-O(-)···C(+)-O electrostatic interaction. In contrast, the results were consistent with the operation of n S → π C O = * stabilizing orbital interactions. Further support for this hypothesis was obtained from the increased C=O bond lengths in these four conformations relative to the other conformations, and by the torsional angle distortion away from ideal geometry, presumably to maximize the stabilizing orbital interaction. We propose that this conformational preference is a manifestation of a generalized exo-anomeric effect. The longer C2-S bond in the axial isomers was also interpreted in terms of a stabilizing π C=O → σ C-S * interaction, analogous to an endo-anomeric interaction. Comparison of the computational results to available experimental data on the conformational equilibrium of each diastereomer in solution suggests which conformers are present in each of the equilibria. The available data for the solid state indicate that the RR and RS isomers both crystallize in high energy conformations, stabilized by intermolecular interactions.Résumé : On a fait appel à des calculs ab initio de densité fonctionnelle pour faire l'analyse conformationnelle de la 2-phénylsulfinylcyclohexanone. On a fait des calculs sur six conformations qui correspondent aux isomères axial/équa-torial et de rotation autour de la liaison C2-S pour chacun des diastéréoisomères RR et RS et on a examiné les résul-tats en fonction des énergies relatives, des interactions électrostatiques, des interactions d'orbitales et des variations de géométrie. La conformation d'énergie globale minimale est celle de l'isomère RS portant le substituant phénylsulfinyle en position équatoriale avec l'oxygène du sulfinyle dans une orientation anti par rapport à l'atome de carbone du carbonyle. Des trois autres conformations de faible énergie, une seule comporte un arrangement gauche de ces atomes et on n'a trouvé des données suggérant l'existence d'une interaction électrostatique S-O(-)···C(+)-O que pour une seule des quatre conformations de basse énergie. Par ailleurs, les résultats sont en accord avec l'opération d'interactions d'orbitales stabilisantes n S → π C O = * . On a obtenu une confirmation supplémentaire pour cette hypothèse dans l'augmentation des longue...

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“…1b) that leads to the preferred stabilization for the larger halogens, the overlap between the lone pair orbital and the π* C=O orbital being less in the equatorial conformers. The conformational studies have been extended to systems containing substituents that are rotors, e.g., X = OR, NMe 2 , SR, and SeR, [5][6][7][8][9][10][11] and it appears that the increased axial preference for the heavier chalcogen substituents is due to the increased non-bonded repulsion with the carbonyl group in the equatorial conformer. 5,11 However, theories of stabilizing orbital interactions continued to be advanced.…”

Section: Introductionmentioning

confidence: 99%

A generalized exo‐anomeric effect. Substituent and solvent effects on the conformational equilibria of 2‐(arylseleno)cyclohexanones

Mcleod

Johnston

Pinto

2000

Israel Journal of Chemistry

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The effects of substitution and solvent on the conformational equilibria of 2-[(4-R-substituted-phenyl)seleno]cyclohexanones are described. The conformational equilibria were determined by comparison of the linewidths of the H-2 resonances in the 1 H NMR spectra of the conformationally averaged systems with those of the anancomeric (highly biased) 4-isopropyl-2-substituted cyclohexanones. The substituent (R = NMe 2 , OMe, Me, H, F, Cl, CF 3 , NO 2 ) and solvent ((CD 3 ) 2 CO, CD 3 CN, CD 2 Cl 2 , CDCl 3 ) effects are discussed in terms of electrostatic effects and the possible stabilizing orbital interactions. The values of K eq (axial-equatorial) increase as the substituent becomes more electron withdrawing, in agreement with the dominance of n Se →π* C=O or σ C-Se →π* C=O orbital interactions in the axial conformers. The increase in the proportion of the equatorial isomers in more polar solvents for a given substituent suggests a damping of the dipolar interactions in the equatorial isomers. However, the proportion of the equatorial isomers in a given solvent increases as the substituent becomes more electron withdrawing, indicating that electrostatic interactions do not dominate in controlling the conformational equilibria. Analysis of the equilibrium data by means of a dual substituent parameter approach indicates the best correlation with σ I and σ + R substituent constants in CD 2 Cl 2 and with σ I and σ o R substituent constants in CD 3 CN, with similar sensitivities to the resonance and polar effects. The correlations are interpreted in terms of accommodation of effective positive charge on the selenium atom in the axial isomers in CD 2 Cl 2 , and a lesser sensitivity to the buildup of positive charge in the more polar solvent CD 3 CN. Comparison of the IR ν CO -stretching frequencies for the axial and equatorial ArSe-substituted anancomeric systems (R = NO 2 , NMe 2 ) indicates a higher stretching frequency for the NO 2 -substituted isomers. In the case of the NMe 2 -substituted compounds, ν CO appears at a higher frequency in the equatorial isomer, whereas in the case of the NO 2 -substituted compounds, ν CO is less sensitive to the axial or equatorial orientation of the substituent. The results are consistent with the operation of n Se →π* C=O or σ C-Se →π* C=O orbital interactions in the axial isomers. The J C2-H2 values in the axially-substituted anancomeric isomers are of greater magnitude than those in the equatorially-substituted isomers, which is also consistent with the operation of the orbital interactions described above. There is, however, no marked substituent effect on the J C2-H2 values within the series of axial or equatorial isomers. We argue that this does not support the dominance of σ C-Se →π* C=O orbital interactions. Examination of crystal structures reported in the literature for related compounds indicates a particular gauche orientation about the C 2 -Se bond, which lends further support to the operation of an n Se →π* C=O orbital interaction. We suggest that the latter interacti...

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Alcoxy-2, aryloxy-2, acyloxy-2 cyclohexanones. Synthèse et étude de leur équilibre conformationnel

Cited by 20 publications

References 7 publications

On the purported axial preference in 2-methylthio and 2-methoxycyclohex-anones: steric effects versus orbital interactions

On the purported axial preference in 2-methylthio and 2-methoxycyclohex-anones: steric effects versus orbital interactions

Ab initio DFT calculations of the configurational and conformational preferences of 2-phenylsulfinylcyclohexanones Evidence for "exo-anomeric" interactions

A generalized exo‐anomeric effect. Substituent and solvent effects on the conformational equilibria of 2‐(arylseleno)cyclohexanones

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Alcoxy-2, aryloxy-2, acyloxy-2 cyclohexanones. Synthèse et étude de leur équilibre conformationnel

Cited by 20 publications

References 7 publications

On the purported axial preference in 2-methylthio and 2-methoxycyclohex-anones: steric effects versus orbital interactions

On the purported axial preference in 2-methylthio and 2-methoxycyclohex-anones: steric effects versus orbital interactions

Ab initio DFT calculations of the configurational and conformational preferences of 2-phenylsulfinylcyclohexanones  Evidence for "exo-anomeric" interactions

A generalized exo‐anomeric effect. Substituent and solvent effects on the conformational equilibria of 2‐(arylseleno)cyclohexanones

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Ab initio DFT calculations of the configurational and conformational preferences of 2-phenylsulfinylcyclohexanones Evidence for "exo-anomeric" interactions