Low temperature carbon-13 magnetic resonance detection of axial conformers in vinyl- and formylcyclohexane: a deshielding γ–gauche effect

1982 ◽  
Vol 60 (23) ◽  
pp. 2908-2913 ◽  
Author(s):  
G. W. Buchanan
Keyword(s):  
Magnetic Resonance ◽  
Low Temperature ◽  
Substituent Effects ◽  
Free Energies ◽  
Gauche Effect ◽  
High Preference ◽  
Resonance Detection ◽  
C Nmr

Using 50.3 MHz 13C nmr at 173 K, distinct resonances for axial conformers of vinyl- and formylcyclohexane have been obtained. Substituent effects for axial and equatorial substitution of these groups have been derived. A deshielding γ–gauche effect was found for the axial substituent carbon of formylcyclohexane, a result attributed to the high preference for rotamers in which the formyl proton does not sterically interfere with syn-axial protons at C-3 and C-5 of the ring. Conformational free energies for the vinyl and formyl groups have been estimated to be 1.49 and 0.84 kcal/mol respectively.

Application of 13C nuclear magnetic resonance to the conformational analysis of vicinally di- and trisubstituted cyclohexanes: halohydrins, methoxyhalohydrins, and their acetates

1985 ◽  
Vol 63 (8) ◽  
pp. 2143-2148 ◽  
Author(s):  
G. W. Buchanan ◽  
J. W. Bovenkamp ◽  
A. Rodrigue ◽  
R. A. B. Bannard ◽  
R. Y. Moir
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Low Temperature ◽  
Chemical Shifts ◽  
Resonance Spectroscopy ◽  
Free Energies ◽  
Relative Peak Area ◽  
13C Nuclear Magnetic Resonance ◽  
Conformational Equilibria ◽  
Nuclear Magnetic

Low temperature 13C nuclear magnetic resonance spectroscopy has been employed to obtain the chemical shifts and to examine the conformational equilibria of the four chlorohydrins and bromohydrins of 3-methoxycyclohexene. The corresponding acetates and the unsubstituted halohydrins have also been examined. The observed chemical shifts were compared with those calculated from additivity considerations. Limitations of this approach are discussed. Relative peak area measurements have been used to obtain conformational free energies in favourable cases.

The conformational properties of seven-membered heterocycles: 1,3-dioxacyclohept-5-ene and its 2-substituted derivatives

1981 ◽  
Vol 59 (15) ◽  
pp. 2283-2289 ◽  
Author(s):  
R. St-Amour ◽  
M. St-Jacques
Keyword(s):  
Low Temperature ◽  
Dynamic Properties ◽  
Substituent Effects ◽  
Dynamic Processes ◽  
Stable Conformation ◽  
Spectral Changes ◽  
Conformational Properties ◽  
C Nmr

1,3-Dioxacycloheptene and its 2-CH3, 2-OCH3, 2-t-Bu, and 2,2-dimethyl derivatives were studied by 1H and 13C dnmr methods. Substituent effects and the interpretation of spectral changes in 13C nmr at low temperature allow the determination of the most stable conformation of these compounds (TB for 1–4b and C for 5b) and the characterization of the dynamic processes observed for 2b, 4b, and 5b. The differences between the conformational and dynamic properties of the above compounds and their benzo analogs are rationalized in terms of different torsional interactions in the two series.

Conformational analysis of substituted 1,2-oxathiane 2-oxides by 13C and 1H nuclear magnetic resonance spectroscopy

1977 ◽  
Vol 55 (1) ◽  
pp. 44-49 ◽  
Author(s):  
G. W. Buchanan ◽  
N. K. Sharma ◽  
F. De Reinach-Hirtzbach ◽  
T. Durst
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Magnetic Resonance Spectroscopy ◽  
Conformational Analysis ◽  
Nuclear Magnetic Resonance Spectroscopy ◽  
Axial Orientation ◽  
Resonance Spectroscopy ◽  
High Preference ◽  
1H Nuclear Magnetic Resonance ◽  
C Nmr

1H and 13C nmr results for 1,2-oxathiane 2-oxide and eight derivatives are reported. It is concluded that these molecules have a high preference for chair forms with axial S=O groups, even when a sterically bulky group such as phenyl is substituted in a syn-axial orientation to the exocyclic oxygen.

Novel stereochemical equilibria in crown ethers. Detection of additional conformations of cis-syn-cis- and cis-anti-cis-dicyclohexano-18-crown-6 by 100.6-MHz 13C nuclear magnetic resonance at 173 K

1985 ◽  
Vol 63 (10) ◽  
pp. 2747-2751 ◽  
Author(s):  
G. W. Buchanan ◽  
K. Bourque ◽  
J. W. Bovenkamp ◽  
A. Rodrigue
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Free Energy ◽  
Magnetic Resonance ◽  
Low Temperature ◽  
Crown Ethers ◽  
High Field ◽  
13C Nuclear Magnetic Resonance ◽  
Conformational Equilibria ◽  
Conformational Free Energy ◽  
C Nmr

High field, 13C nmr has been utilized for the analysis of new conformational equilibria in each of the title crown ethers at low temperature. Evidence indicates that these equilibria arise from restricted rotation in the macrocyclic portions of these molecules. The conformational free energy differences between the isomers are small (0.1–0.3 kcal/mol) while barriers to their interconversion are of the order of 8.5–9.0 kcal/mol. Comparisons are made with the degenerate equilibria involving inversion of the cyclohexane rings.

13C nuclear magnetic resonance studies. 55. A comparison of the stereochemical dependence of γ- and δ-substituent effects on 13C shieldings in several norbornanols and norbornenols

1976 ◽  
Vol 54 (8) ◽  
pp. 1211-1221 ◽  
Author(s):  
J. B. Stothers ◽  
C. T. Tan ◽  
K. C. Teo
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Nmr Spectra ◽  
Substituent Effects ◽  
Magnetic Resonance Studies ◽  
Considerable Potential ◽  
13C Nuclear Magnetic Resonance ◽  
Insight Into ◽  
C Nmr ◽  
Nuclear Magnetic

The 13C nmr spectra of a series of 50 methyl substituted norbornanols have been determined to gain further insight into the nature of stereochemical effects on the shieldings of carbons having closely neighboring substituents. The relatively rigid norbornyl skeleton permits examination of a variety of orientations of substituents separated by three and four bonds, the γ and δ interactions, respectively. While methyl carbons close to γ substituents exhibit upfield shifts, as is well established, methyl carbons close to δ substituents are significantly deshielded. Even more striking shifts are found for the carbons bearing these closely lying groups. The penultimate carbons in a fragment having a δ interaction between terminal groups show deviations of up to +11 ppm from the shieldings predicted by simple additivity. For fragments having a corresponding γ interaction, the penultimate carbons absorb as much as −10 ppm from the values expected by additivity. These deviations have considerable potential for stereochemical assignments and offer a challenge for theoretical interpretation.Some norbornenols and the acetates of several of the norbornanols were also included in this series and the latter shieldings are compared briefly with those observed for the parent alcohols.

scholarly journals 13C nuclear magnetic resonance studies. 64. The 13C spectra of a variety of bicyclo[3.2.1]octanols

1977 ◽  
Vol 55 (5) ◽  
pp. 841-848 ◽  
Author(s):  
J. B. Stothers ◽  
C. T. Tan
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Nmr Spectra ◽  
Substituent Effects ◽  
Ring System ◽  
Hydroxyl Group ◽  
Magnetic Resonance Studies ◽  
13C Nuclear Magnetic Resonance ◽  
C Nmr ◽  
Shielding Effects

The 13C nmr spectra of a series of 20 bicyclo[3.2.1]octanols and -octenols have been determined to examine the shielding effects of the hydroxyl group on the skeletal carbons in this ring system. For comparison, the previously unreported data for a few closely related alcohols in the [2.1.1], [2.2.1], and [3.2.2] systems were also collected. The utility of these substituent effects for configuraional and conformational assignments is discussed.

scholarly journals Destabilized carbocations. Nuclear magnetic resonance detection and reactivities of aryl α-thioformamidyl cations

1987 ◽  
Vol 65 (8) ◽  
pp. 1800-1803 ◽  
Author(s):  
F. J. Ablenas ◽  
B. E. George ◽  
M. Maleki ◽  
R. Jain ◽  
A. C. Hopkinson ◽  
...  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Low Temperature ◽  
Magnetic Resonance Spectroscopy ◽  
Nuclear Magnetic Resonance Spectroscopy ◽  
Resonance Spectroscopy ◽  
Resonance Detection ◽  
Nuclear Magnetic

A series of α-aryl and diarylthioformamidyl cations were observed by low-temperature nuclear magnetic resonance spectroscopy. These ions undergo efficient cyclization and deprotonation to give benzothiophenes.

1H and 13C dynamic nuclear magnetic resonance study of hindered rotation in thiobenzoylpiperidines and thiobenzoylmorpholines. Correlation between barrier heights of amides and thioamides

1977 ◽  
Vol 55 (14) ◽  
pp. 2649-2655 ◽  
Author(s):  
Carla Piccinni-Leopardi ◽  
Omer Fabre ◽  
Daniel Zimmermann ◽  
Jacques Reisse ◽  
F. Cornea ◽  
...  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Linear Correlation ◽  
Substituent Effects ◽  
Nuclear Magnetic Resonance Study ◽  
Free Energies ◽  
Magnetic Resonance Study ◽  
Hindered Rotation ◽  
Barrier Heights ◽  
Dynamic Nuclear Magnetic Resonance

The free energies of activation for hindered rotation around the C—N bond have been determined for a series of N,N-disubstituted thioamides by means of 13C and 1H dynamic nmr.A comparison between barriers for 20 amides and the corresponding thioamides, studied under similar conditions, has been drawn up using both our results and data obtained from the literature. An excellent linear correlation has been obtained. The same correlation also holds for primary (thio)amides and seems to be of general significance. Substituent effects on the barrier heights of thioamides and amides are discussed in connection with some particular cases.

A Circular-Disk Dielectric Resonator for Low-Temperature Magnetic Resonance Measurements at Millimeter and Sub-Millimeter Wavelengths

2008 ◽  
Vol 67 (14) ◽  
pp. 1239-1245
Author(s):  
V. N. Derkach ◽  
T. V. Bagmut ◽  
R. V. Golovashchenko ◽  
V. G. Korzh ◽  
S. V. Nedukh ◽  
...  
Keyword(s):  
Magnetic Resonance ◽  
Low Temperature ◽  
Dielectric Resonator ◽  
Circular Disk ◽  
Millimeter Wavelengths
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