13C Nuclear Magnetic Resonance Studies of Methylated Anthracenes

1975 ◽  
Vol 53 (13) ◽  
pp. 1958-1969 ◽  
Author(s):  
Myron L. Caspar ◽  
J. B. Stothers ◽  
Nancy K. Wilson
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Regression Analysis ◽  
Standard Deviation ◽  
Magnetic Resonance ◽  
Substituent Effects ◽  
Methyl Substituent ◽  
Magnetic Resonance Studies ◽  
Charge Densities ◽  
13C Nuclear Magnetic Resonance ◽  
Proton Decoupling

The 13C n.m.r. spectra of anthracene and 11 methylated anthracenes have been examined. Analysis of the 1H spectra allowed unequivocal assignments for most of the protonated carbons by selective proton decoupling. Parameters describing the methyl substituent effects on the aryl carbon shieldings were defined and refined by regression analysis so that the 13C shieldings were predicted for 67 independent aryl positions in anthracenes without peri-methyls with a standard deviation of 0.12 p.p.m. Peri methyl-methyl interactions cause considerable deviations from the predicted substituent effects. The relationships of the 13C shieldings to charge densities calculated by the CNDO/2 method were briefly examined. Syntheses of 2,7,9-trimethyl-, 1,4,5,8- and 1,4,5,9-tetramethyl-, and 1,4,5,8,9-pentamethylanthracene are described.

13C Nuclear Magnetic Resonance Studies. 38. Examination of the Long-range Shielding Effects of the Hydroxyl Group in Alicyclic Systems

1974 ◽  
Vol 52 (6) ◽  
pp. 870-878 ◽  
Author(s):  
S. H. Grover ◽  
J. B. Stothers
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Spectral Analysis ◽  
Magnetic Resonance ◽  
Substituent Effects ◽  
Hydroxyl Group ◽  
Magnetic Resonance Studies ◽  
13C Nuclear Magnetic Resonance ◽  
Steric Crowding ◽  
Direct Contrast ◽  
Shielding Effects

The substituent effects of the hydroxyl group on the 13C shieldings of the trans-decalols and the 10-methyl-trans-decalols have been determined. The shifts for the carbons three and four bonds from the site of substitution depend strongly on their orientation with respect to the hydroxyl group. While the latter have not been widely recognized, these δ effects are valuable for spectral analysis and stereochemical assignments since these range up to 3.4 p.p.m. In direct contrast to the well established trends for γ effects, steric crowding of δ nuclei causes marked downfield shifts. The corresponding effects in several steroids are illustrated.

13C Nuclear magnetic resonance studies. XII. Conformational effects on 13C shieldings in alicyclic oxygenated compounds

1969 ◽  
Vol 47 (17) ◽  
pp. 3113-3118 ◽  
Author(s):  
G. W. Buchanan ◽  
J. B. Stothers ◽  
Siu-Tzyy Wu
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Similar Data ◽  
Free Energies ◽  
Methyl Substituent ◽  
Decoupling Method ◽  
Magnetic Resonance Studies ◽  
Oxygenated Compounds ◽  
Conformational Effects ◽  
13C Nuclear Magnetic Resonance ◽  
Proton Decoupling

The 13C shieldings of the primary carbinyl carbons in cyclohexylmethanol, its acetate and methyl ether as well as those for the corresponding carbon in their 4-t-butyl derivatives have been measured at 15.1 MHz using the 'proton-decoupling' method. Similar data for the 1-methyl-4-t-butylcyclohexylcarbinols and their acetates were obtained to examine the influence of the additional methyl substituent. Possible origins of the observed conformational effects on 13C nuclear shieldings are considered. The 1H results for the methylene protons in these carbinyl groups are also presented and discussed. These results, which permit estimations of the conformational free energies (−ΔG°) of the —CH2OR groupings (R = H, Ac, Me), are presented to illustrate the 13C approach to conformational analysis.

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.

Nuclear Magnetic Resonance Chemical Shifts of some Monosubstituted Isothiazoles

1975 ◽  
Vol 53 (4) ◽  
pp. 596-603 ◽  
Author(s):  
Roderick E. Wasylishen ◽  
Thomas R. Clem ◽  
Edwin D. Becker
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shifts ◽  
Substituent Effects ◽  
Charge Densities ◽  
Monosubstituted Benzenes ◽  
Proton Chemical Shifts ◽  
Nuclear Magnetic

Carbon-13 and proton chemical shifts have been measured for several monosubstituted isothiazoles. Substituent effects upon these chemical shifts are compared with those observed for monosubstituted benzenes, pyridines, and thiophenes. In general the observed substituent effects in the isothiazoles and thiophenes closely parallel one another. Correlations between the observed carbon-13 Chemical shifts and CNDO/2 calculated charge densities are examined.

X-Ray crystallographic and 13C nuclear magnetic resonance studies of 3,4,5,6-tetrahydro-2H-1,3,4-oxadiazin-2-ones derived from ephedrine and pseudoephedrine

Tetrahedron ◽  
2001 ◽  
Vol 57 (49) ◽  
pp. 9789-9798 ◽  
Author(s):  
Shawn R Hitchcock ◽  
George P Nora ◽  
David M Casper ◽  
Michael D Squire ◽  
Christopher D Maroules ◽  
...  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Magnetic Resonance Studies ◽  
X Ray ◽  
13C Nuclear Magnetic Resonance ◽  
Nuclear Magnetic

13C Nuclear Magnetic Resonance Studies. XVI. 13C Spectra of some Substituted Acrylic Acids and their Methyl Esters. A Correlation of Olefinic Shieldings in α,β-unsaturated Carbonyl Systems

1972 ◽  
Vol 50 (5) ◽  
pp. 601-611 ◽  
Author(s):  
H. Brouwer ◽  
J. B. Stothers
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Regression Analysis ◽  
Methyl Esters ◽  
Linear Regression Analysis ◽  
Magnetic Resonance Studies ◽  
Carbonyl Derivatives ◽  
Solvent Dependence ◽  
13C Nuclear Magnetic Resonance ◽  
Unsaturated Carboxylic Acids ◽  
Acrylic Acids

The carbon-13 n.m.r. spectra of 26 α,β-unsaturated methyl esters and 16 substituted acrylic acids have been determined and the 13C shieldings are discussed. These data are compared with the recently reported values for several α,β-unsaturated carboxylic acids. Linear regression analysis of the olefinic shielding data for several α,β-unsaturated carbonyl derivatives yields a set of parameters which correlate the results with reasonable precision. The solvent dependence of the 13C shieldings of acrylic acid and methyl acrylate has been examined briefly. The proton results for the methyl esters are discussed briefly.

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