Solvent shifts of proton resonances induced by benzene and pyridine in epoxides and ethers. An aid to structure elucidation

Williams, Dudley H.; Ronayne, J. W.; Moore, Harold W.; Shelden, H. Raymond

doi:10.1021/jo01267a012

Cited by 18 publications

(4 citation statements)

References 1 publication

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“…While aromatic solvents like benzene usually line up in a plane parallel to a polar solvent molecule, giving rise to upfield shifts, solvation of pyridine is known to either shield or deshield the protons of the solute. 6 Owing to its unsymmetrical electronic structure, pyridine may specifically interact with the oxygens of the polyether ring, and the observed proton shifts will depend strongly on the average orientation of the pyridine ring with respect to'the various protons. On addition of fluorenylsodium (1:1 ratio with the ether) the two peaks are now shifted much further upfield, namely, to 228 and 193 cps.…”

Section: Resultsmentioning

confidence: 99%

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Binding of cyclic polyethers to ion pairs of carbanion alkali salts

Wong¹,

Konizer²,

Smid³

1970

J. Am. Chem. Soc.

125

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Complexation of cyclic polyethers of the "crown" type to ion pairs of fluorenyl alkali salts was studied in ethereal solvents and pyridine by nmr and by uv-visible spectroscopy. The absorption spectra of these complexes are identical with the spectra of the solvent-separated ion pairs of the fluorenyl alkali salts. The complexing with the ion pairs leads to strong upfield shifts in the nmr spectrum of the polyether ring protons. The binding of fluorenylsodium with dimethyldibenzo-18-crown-6 is so strong that a slow exchange process with free cyclic polyether is observed, with an activation energy of 12.5 kcal/mole. The selectivity of this particular cyclic polyether with respect to alkali ions in THF was found to be Na+ » K+ > Cs+ > Li+, but this sequence is dependent on the solvent medium. In oxetane, the cyclic polyether prefers the fluorenylpotassium above the sodium salt. The complexing with some other cyclic polyethers was also investigated.

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Section: Resultsmentioning

confidence: 99%

“…Found: C, 49.16; , 7.60. Nmr (in CC14): 5 0.43 (s, 6 H, Me2Si), 1.86 (s with shoulder at ca. 1.84, 8 H, SiC//2 + CH8-C), 4.95 and 5.05 ppm,…”

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confidence: 99%

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Binding of cyclic polyethers to ion pairs of carbanion alkali salts

Wong¹,

Konizer²,

Smid³

1970

J. Am. Chem. Soc.

125

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“…While this coupling is not visible in the epoxides 3 and 4 due to signal overlap, a clear coupling constant of 3.4 Hz was measured for epoxide 6 . To measure the H-4 to H-5 coupling in epoxides 3 and 4 , the spectra were measured in benzene- d 6 , which is known to induce shifts in proton resonances relative to chlorinated solvents for six membered ring epoxides . The spectra clearly show that the signal for H-5 is coupled to H-4 with a coupling of 4.0 Hz in the β isomer, while in the α isomer, no coupling is observed.…”

Section: Resultsmentioning

confidence: 99%

The Stereochemical Outcome of Electrophilic Addition Reactions on the 5,6-Double Bond in the Spinosyns

and¹,

Graupner²,

and³

et al. 2001

J. Org. Chem.

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The electrophilic addition of reagents to the 5,6-double bond in spinosyn A and spinosyn D systems occurred with high pi-diastereofacial selectivity. Addition occurred preferentially from the beta face of the molecule with selectivities ranging from 5:1 to better than 30:1. Various NMR properties were investigated in order to distinguish the beta and alpha isomers with the help of theoretical models of the products. These NMR properties include a (13)C gamma effect to C-11 and vicinal coupling between H-4 and H-5. To help rationalize the selectivity, computational studies on the transition states for epoxidation were calculated using density functional theory. The results indicate that beta epoxidation is favored and that the geometries of the transition structures are consistent with torsional steering being the source of the selectivity.

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Oxiranes

Bartók¹,

Lang²

1985

Chemistry of Heterocyclic Compounds: A Series of Monographs

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Solvent shifts of proton resonances induced by benzene and pyridine in epoxides and ethers. An aid to structure elucidation

Cited by 18 publications

References 1 publication

Binding of cyclic polyethers to ion pairs of carbanion alkali salts

Binding of cyclic polyethers to ion pairs of carbanion alkali salts

The Stereochemical Outcome of Electrophilic Addition Reactions on the 5,6-Double Bond in the Spinosyns

Oxiranes

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