13 C n.m.r. studies. IX. Carbonyl carbon shieldings of some cyclopropyl ketones

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The 15.1 MHz I3C nuclear magnetic resonance spectra of 13 aliphatic and alicyclic ketones having an olefinic bond in the D, y position with respect to the carbonyl group have been recorded and the carbonyl shieldings measured. The major aim of this study was to investigate the possibility of detecting homoconjugative interactions between the n-systems by comparing the carbonyl shieldings with those for thc corresponding saturated and a,D-unsaturated systems. Some evidence of homoconjugation is presented on the basis of our previous interpretation of the factors governing carbonyl shieldings. A qualitative assessment of the observed geometrical dependence of the effect is offered.

Section: Introductionmentioning

confidence: 52%

Section: Introductionmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

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¹³C Nuclear magnetic resonance studies. XIII. ¹³C Carbonyl carbon shieldings of some β,γ-unsaturated ketones

Gurudata¹,

Stothers²

1969

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“…This equality is probably due to the solute-solvent interactions. Normally, the shieldings of ester and acid carbonyl carbons are separated by about 7ppm (3,4). To understand this feature, we prepared ( 5 ) and examined the spectrum of monoethyl phthalate.…”

Section: Resultsmentioning

confidence: 99%

Synthesis and carbon-13 nuclear magnetic resonance spectra of monoethyl 4-nitro and 4-amino phthalates

Seshadri¹,

Bacha²

1980

. Can. J. Chem. 58,617 (1980). Carbon-13 nmr has been found to be an effective spectroscopic method for measuring the ratio of isomeric monoethyl esters resulting from the esterification of 4-nitrophthalic acid, the alcoholysis of Qnitrophthalic anhydride, and the catalytic reduction of monoethyl 4-nitrophthalates. Precise values ofthe 13C chemical shifts for I-ethyl and 2-ethyl Cnitrophthalate and the corresponding 4-aminophthalates were determined; the shielding parameters are explained in terms of known structural effects. Details of the esterification, alcoholysis, reduction reactions, and the isolation of 1-ethyl 4-nitrophthalate are described.

“…From our investigatioils of certain alicyclic systems (7,8) by carbon magnetic resonance (6.m.r.) spectroscopy we were led to an examination of the alicyclic alcohols in which were included the cis-and trans-4-t-butylcyclohexanols.…”

Section: Introductionmentioning

confidence: 99%

¹³C Nuclear magnetic resonance studies. XIV. Conformational effects on carbinyl carbon shieldings in cyclohexanols and derivatives

Buchanan¹,

Stothers²

1969

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The I3C shieldings of the alicyclic carbons bearing oxygen in several cyclohexanols, their acetates and methyl ethers depend on the orientation of the oxygen functions. The compounds examined include the cis-and trans-4-alkyl derivatives in which the alkyl groups are t-butyl, i-propyl, ethyl and methyl, as well as the 3-t-butyl isomers. The results for the parent compounds are employed for the estimation of the conformational free energies of the hydroxyl, acetoxyl, and methoxyl groups, and serve to establish that I3C magnetic resonance (c.m.r.) spectroscopy offers a new approach to conformational analysis. The data were obtained using the decoupling technique and materials containing I3C in natural abundance.Canadian Journal of Chemistry, 47, 3605 (1969) IntroductionOver the past few years sufficient evidence has been accumulated to establish that carbon shieldings depend, at least in part, on molecular geometry and conformation (1-6). From our investigatioils of certain alicyclic systems (7,8) by carbon magnetic resonance (6.m.r.) spectroscopy we were led to an examination of the alicyclic alcohols in which were included the cis-and trans-4-t-butylcyclohexanols. The shieldings of the carbinyl carbons in these isomers were found to differ by ca. 5 p.p.m. (3) indicating that c.m.r. techniques have promise as an additional tool for conformational analysis. In fact, the method constitutes a new approach to this aspect of stereochemical studies because the pronounced differences observed are a function of substituent orientation entirely since the position of the carbon nucleus of interest is unchanged relative to the other atoms in the molecule for both epimers. Since the difference is relatively large, its measurement with refined techniques may be superior to other nuclear magnetic resonance (n.m.r.) methods.To determine the utility of the approach for conformational analysis and to confirm that the shielding differences are primarily due to conformational effects we examined the 4-alkyl series including the isopropyl, ethyl, and methyl derivatives as well as the 3-t-butyl isomers. The acetates and methyl ethers were also measured to assess the importance of hydrogen bonding contribu-