Carbonyl Carbon Chemical Shift Tensors for a Typical Aryl Aldehyde and Formaldehyde. NMR Studies of the Isolated 13C-2H Spin Pair of 3,4-Dibenzyloxybenzaldehyde-13C.alpha.2H.alpha.

1995 ◽  
Vol 99 (43) ◽  
pp. 15806-15813 ◽  
Author(s):  
Gang Wu ◽  
Michael D. Lumsden ◽  
Gabriel C. Ossenkamp ◽  
Klaus Eichele ◽  
Roderick E. Wasylishen
Keyword(s):  
Chemical Shift ◽  
Carbonyl Carbon ◽  
Nmr Studies ◽  
Chemical Shift Tensors ◽  
Spin Pair ◽  
Aryl Aldehyde ◽  
Carbon Chemical Shift

Deshielding γ–gauche effects in 13C magnetic resonance: a comparison of the conformational behaviour of the acetyl group in cyclohexane and 5-substituted-1,3-dioxane systems

1984 ◽  
Vol 62 (7) ◽  
pp. 1308-1311 ◽  
Author(s):  
G. W. Buchanan ◽  
S. H. Preusser ◽  
V. L. Webb
Keyword(s):  
Magnetic Resonance ◽  
Chemical Shift ◽  
Low Temperature ◽  
Direct Measurement ◽  
Carbonyl Carbon ◽  
Acetyl Group ◽  
Carbon Chemical Shift ◽  
Reported Data

Low temperature (173 K) 13C spectra of acetylcyclohexane, 1-acetyl-1-methylcyclohexane, and 5-acetyl-5-methyl-1,3-dioxane are reported. Data permit the first direct measurement of −ΔG0 for the acetyl group bonded to cyclohexane. The value obtained, 1.02 ± 0.05 kcal/mol in CS2–CD2Cl2 solution, is considerably lower than that determined by equilibration methods. Factors contributing to observed axial–equatorial carbonyl carbon chemical shift differences for substituted cyclohexanes and 1,3-dioxanes are discussed.

Carbonyl Carbon and Nitrogen Chemical Shift Tensors of the Amide Fragment of Acetanilide and N-Methylacetanilide

1994 ◽  
Vol 116 (4) ◽  
pp. 1403-1413 ◽  
Author(s):  
Michael D. Lumsden ◽  
Roderick E. Wasylishen ◽  
Klaus Eichele ◽  
Michael Schindler ◽  
Glenn H. Penner ◽  
...  
Keyword(s):  
Chemical Shift ◽  
Carbonyl Carbon ◽  
Chemical Shift Tensors ◽  
Carbon And Nitrogen ◽  
Amide Fragment

A solid-state 13C NMR and theoretical investigation of carbonyl and thiocarbonyl carbon chemical shift tensors

1995 ◽  
Vol 73 (4) ◽  
pp. 604-613 ◽  
Author(s):  
Christopher W. Kirby ◽  
Michael D. Lumsden ◽  
Roderick E. Wasylishen
Keyword(s):  
Solid State ◽  
Chemical Shift ◽  
Ab Initio ◽  
Principal Axis ◽  
Comparative Investigation ◽  
Conclusive Evidence ◽  
Carbon Nucleus ◽  
Chemical Shift Tensors ◽  
Carbon Chemical Shift ◽  
C Nmr

The carbon chemical shift tensors of the carbonyl and thiocarbonyl groups of acetamide, thioacetamide, thioacetanilide, 4′-methoxyacetanilide, and 4′-methoxythioacetanilide have been experimentally determined using dipolar – chemical shift solid-state 13C NMR spectroscopy. The magnitudes of the three principal components of the carbon chemical shift tensors are found to exhibit marked variations between the carbonyl and thiocarbonyl functionalities. However, in contrast to the conclusions of an earlier comparative investigation involving benzophenone and thiobenzophenone, the orientations of the principal axis systems of these chemical shift tensors are found to be similar. These experimental results represent the first complete characterizations of the carbon chemical shift tensor in organic thiocarbonyls. The results of our ab initio GIAO and LORG calculations of carbon chemical shielding tensors in formaldehyde, thioformaldehyde, formamide, and thioformamide as well as in acetamide and thioacetamide are in qualitative agreement with experiment. The findings of the present investigation provide conclusive evidence that the well-known isotropic deshielding of the carbon nucleus in the C=S group relative to C=O is primarily attributable to the decreased energy associated with the σ ↔ π* excitation within the thiocarbonyl fragment. This result is in contrast with the conventional interpretation that the deshielding originates from a red shift in the C=S HOMO–UMO n → π* transition. Keywords: chemical shift tensors, solid-state 13C NMR, carbonyls, thiocarbonyls, ab initio calculations.

The carbonyl carbon-13 chemical shift tensors of five peptides determined from nitrogen-15 dipole-coupled chemical shift powder patterns

1987 ◽  
Vol 109 (20) ◽  
pp. 5956-5962 ◽  
Author(s):  
Terrence G. Oas ◽  
Cynthia J. Hartzell ◽  
Thomas J. McMahon ◽  
Gary P. Drobny ◽  
Frederick W. Dahlquist
Keyword(s):  
Chemical Shift ◽  
Carbonyl Carbon ◽  
Chemical Shift Tensors

Phosphorus-31 NMR studies of several phosphines in the solid state

1989 ◽  
Vol 67 (11) ◽  
pp. 1909-1913 ◽  
Author(s):  
Glenn H. Penner ◽  
Roderick E. Wasylishen
Keyword(s):  
Chemical Shift ◽  
Principal Components ◽  
Chemical Shift Tensor ◽  
Cross Polarization ◽  
X Ray Diffraction ◽  
Nmr Studies ◽  
Chemical Shift Tensors ◽  
X Ray ◽  
Cp Mas Nmr ◽  
Proton Decoupling

Phosphorus-31 NMR powder spectra and high resolution MAS spectra have been obtained for a number of solid phosphines under conditions of high-power proton decoupling and cross-polarization. The principal components of the 31P chemical shift tensor obtained from static powder spectra or slow MAS spectra are discussed in terms of the known structures of many of the phosphines. The CP/MAS 31PNMR spectra are used to determine the number of crystallographically nonequivalent molecules in the unit cell. The NMR results are consistent with data available from X-ray diffraction. In one case there is evidence of polymorphism. Keywords: 31P NMR of solid phosphines, principal components of 31P chemical shift tensors, crystallographic nonequivalence from 31P CP/MAS NMR.

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