Proton magnetic resonance spectrum of cellulose triacetate. Temperature effects, the rotational conformation of the 6-acetoxymethyl group, and computer modelling of methyl 4,6-di-O-acetyl-β-glucopyranoside

1985 ◽  
Vol 63 (9) ◽  
pp. 2507-2510 ◽  
Author(s):  
Vanga S. Rao ◽  
Françoise Sauriol ◽  
Arthur S. Perlin ◽  
M. T. Phan Viet
Keyword(s):  
Resonance Spectrum ◽  
Computer Modelling ◽  
Chemical Shifts ◽  
Cellulose Triacetate ◽  
Proton Magnetic Resonance Spectrum ◽  
Spin Coupling ◽  
Supporting Evidence ◽  
Nmr Spectrum ◽  
H Nmr ◽  
Spin Spin Coupling

Pronounced narrowing of the resonance signals in the 400-MHz 1H nmr spectrum of cellulose triacetate in CDCl3 between 25 and 50 °C, as well as shielding and deshielding changes in 1H chemical shifts, suggest that thermal disruption of intermolecular aggregates is accompanied by a conformational modification. Analysis of the spin–spin coupling patterns clearly evident at 50 °C indicates that although there is a reversal in the chemical shifts of H-6R and H-6S relative to those for acetylated D-glucopyranose derivatives, the rotational conformations of the exocyclic 6-acetoxymethyl groups of the polymer and the model compounds all favor RHS and RCS rotameric forms. Supporting evidence for this conclusion is obtained from the 2-dimensional 1H spectrum of a trisaccharide, O-β-D-glucopyranosyl-(1 → 3)-O-β-D-glucopyranosyl-(1→ 4)-O-β-D-glucopyranose undecaacetate. Computer-generated models of methyl 4,6-di-O-acetyl-β-glucopyranoside are examined in relation to the stereochemistry of 6-acetoxymethyl groups.

The planar conformation of 2-methylthiobenzaldehyde in solution

1983 ◽  
Vol 61 (1) ◽  
pp. 26-28
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian
Keyword(s):  
Chemical Shifts ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Spectral Parameters ◽  
H Nmr ◽  
Heavy Atoms ◽  
Planar Conformation ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Infrared Data

The 1H nmr spectral parameters are extracted for a 4 mol% solution of 2-methylthiobenzaldehyde in CCl4 at 305 K. The long-range spin–spin coupling constants involving the aldehydic and methyl protons are consistent only with a preferred conformation in which all heavy atoms are coplanar, as are the chemical shifts of the ring and methyl protons. This conclusion contradicts previous interpretations of the dipole moment, the nmr parameters, and of the infrared data for CCl4 solutions. The present data show that the O-syn and O-anti forms of the compound are present in roughly equal proportions.

Nuclear Magnetic Resonance Spectrum of 1-Hydroxy-2,3-Epoxypropane

1968 ◽  
Vol 22 (6) ◽  
pp. 773-776
Author(s):  
A. Leifer ◽  
H. L. Goldstein
Keyword(s):  
Resonance Spectrum ◽  
Chemical Shifts ◽  
Internal Standard ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Pure Liquid ◽  
Nmr Spectrum ◽  
Hydroxyl Proton ◽  
Spin Coupling Constants ◽  
Experimental Values

The NMR spectrum of pure liquid 1-hydroxy-2,3-epoxypropane has been analyzed quantum mechanically. The analysis is greatly simplified by treating the protons on the propane chain as two separate ABX systems. The chemical shifts at 60 Mcps, relative to the internal standard tetramethylsilane (TMS), and the spin coupling constants were found to be vA = 168.1 cps, vB = 160.5 cps, vX = 188.8 cps, vA' = 232.2 cps, vB' = 212.8 cps, JAB = 5.2 cps, JA'B' = 12.7 cps, JXA = 4.5 cps, JXA' = 2.9 cps, JBX = 2.7 cps, JB'X = 5.3 cps. Using these parameters the calculated frequencies of the spectrum are in excellent agreement with the experimental values. The chemical shift of the hydroxyl proton was found to be 266.8 cps downfield from TMS.

Conformational dependence of long-range spin-spin coupling constants in 2,6-dichlorobenzylfluoride

1969 ◽  
Vol 47 (19) ◽  
pp. 3688-3690 ◽  
Author(s):  
T. Schaefer ◽  
C. M. Wong ◽  
K. C. Tam
Keyword(s):  
Magnetic Resonance ◽  
Long Range ◽  
Proton Magnetic Resonance ◽  
Resonance Spectrum ◽  
Double Resonance ◽  
Proton Magnetic Resonance Spectrum ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling

Double resonance experiments on the proton magnetic resonance spectrum of 2,6-dichlorobenzylfluoride yield the signs of the long-range coupling constants between the ring protons and the fluorine nuclei and protons in the fluoromethyl group. The signs and magnitudes of the long-range couplings are discussed in terms of their dependence on the conformation of the fluoromethyl group.

The probable planarity of 1,2-dimethoxybenzene in solution

1983 ◽  
Vol 61 (2) ◽  
pp. 224-229 ◽  
Author(s):  
Ted Schaefer ◽  
Reino Laatikainen
Keyword(s):  
Benzene Solution ◽  
Theoretical Data ◽  
Spin Coupling ◽  
Coupling Constant ◽  
Nmr Spectrum ◽  
Methyl Group ◽  
H Nmr ◽  
Planar Conformation ◽  
Precise Analysis ◽  
Spin Spin Coupling

A precise analysis of the 1H nmr spectrum of 1,2-dimethoxybenzene in benzene solution yields an accurate value for the proximate spin–spin coupling constant, [Formula: see text], between the ortho ring proton and the methyl protons. The latter also couple to other ring protons and these couplings are assessed. Comparison with some values in other anisole derivatives and with a variety of INDO MO FPT calculations of [Formula: see text] strongly implies the predominance of a planar conformation in solution. This implication disagrees with the interpretation of some other experimental and theoretical data. The mechanism of this proximate coupling is examined by the procedure of Barfield. It seems that the magnitude of the coupling is dominated by interactions involving the orbitals on the carbon atom of the methyl group.

Long-range proton–19F spin–spin coupling interactions in phenyltrifluorosilane

1977 ◽  
Vol 55 (18) ◽  
pp. 3243-3247 ◽  
Author(s):  
William J. E. Parr ◽  
T. Schaefer ◽  
K. Marat
Keyword(s):  
Long Range ◽  
Resonance Spectrum ◽  
Base Point ◽  
Proton Magnetic Resonance Spectrum ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Hindered Rotation ◽  
Spin Coupling Constants ◽  
Spin Spin Coupling ◽  
Coupling Mechanisms

Analysis of the proton magnetic resonance spectrum of phenyltrifluorosilane yields the spin–spin coupling constants between the fluorine nuclei and the protons. These are compared with the analogous long-range coupling constants in benzotrifluoride, toluene, and phenylsilane and are rationalized in terms of coupling mechanisms. The coupling over six bonds is assessed as a base point for the estimation of hindered rotation about the carbon–silicon bond.

73 Ge Nuclear Magnetic Resonance Studies

1971 ◽  
Vol 26 (9) ◽  
pp. 1384-1389 ◽  
Author(s):  
J . Kaufmann ◽  
W. Sahm
Keyword(s):  
Chemical Shifts ◽  
Spin Echo ◽  
Relaxation Times ◽  
Least Square ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Nmr Spectrum ◽  
Spin Coupling Constants ◽  
Spin Echo Technique ◽  
Spin Spin Coupling

Abstract The 73Ge spectra of some germanium-tetra-halides, germanium-tetra-alkyles, and of germanium-tetra-methoxide have been observed. The chemical shifts of these 73Ge NMR-lines were measured as functions of the temperature in the range up to 50 °C. In CS2-and benzene-solutions of Gel4 , two 73Ge-lines were found. The 73Ge NMR-spectrum of Ge(CH3)4 caused by indirect spin-spin-coupling between the 73Ge nucleus and the protons is well resolved. The spin-spin-coupling constants of Ge(CH3)4 and of Ge(OCH3)4, which shows an unresolved spectrum, were evaluated by an iterative least square fitting routine. The relaxation times T2 (in the range 30...740 msec) measured by the Carr-Purcell spin-echo-technique and calculated from the line widths are in good agreement. Precision measurements of the ratios of the Larmor frequencies of 73Ge in GeCl4, 41K in aqueous KF-solution and 2H in pure heavy water lead to a magnetic moment of 73Ge: μ = -(0.876 78 ± 0.000 01) μN (uncorrected).

Some unique properties of in 2-fluorotoluene derivatives. Conformational dependence

1983 ◽  
Vol 61 (1) ◽  
pp. 29-36 ◽  
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian ◽  
Richard P. Veregin ◽  
Reino Laatikainen
Keyword(s):  
Strong Dependence ◽  
Spin Coupling ◽  
Complete Analysis ◽  
Matrix Elements ◽  
Coupling Constant ◽  
Nmr Spectrum ◽  
H Nmr ◽  
Spin Spin Coupling ◽  
Coupling Mechanisms ◽  
Derivatives Of

A complete analysis of the 1H nmr spectrum of 2-fluorotoluene yields [Formula: see text] the spin–spin coupling constant between 19F and the methyl protons, as 1.99 Hz. Analysis of nmr spectra of 21 other derivatives of 2-fluorotoluene shows that [Formula: see text] can vary between 1.69 and 2.55 Hz. This strong dependence on substitution contrasts with the near invariance of other long-range couplings such as [Formula: see text], [Formula: see text], [Formula: see text] The substituent dependence is discussed in terms of coupling mechanisms. INDO MO FPT calculations of [Formula: see text] are inadequate. By means of appropriate model compounds, an adequate empirical conformational dependence is deduced for [Formula: see text] which can be used to reproduce some observed couplings. INDO MO FPT computations, in which certain off-diagonal Fock matrix elements are suppressed, are used to show that spin polarization via interacton of the methyl hydrogen orbitals is a major source of the discrepancy between theory and experiment. Some STO 3G MO calculations are reported for 2-fluorotoluene conformations.

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