1H nuclear magnetic resonance and molecular orbital studies of the internal rotational potential and electron delocalization in triphenylphosphine

1993 ◽  
Vol 71 (5) ◽  
pp. 639-643 ◽  
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian ◽  
Frank E. Hruska
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Molecular Orbital ◽  
Lone Pair ◽  
Electron Delocalization ◽  
Spectral Parameters ◽  
Internal Motions ◽  
Diamagnetic Anisotropy ◽  
1H Nuclear Magnetic Resonance ◽  
Nuclear Magnetic

The 1H nuclear magnetic resonance spectral parameters are reported for triphenylphosphine as solutions in CS2/C6D12 and acetone-d6 at 300 K. The internal rotational potential opposing torsion about the P—C bond is computed by AMI and STO-3G MO methods. The computed potentials are used to calculate the average shielding of the para protons caused by the diamagnetic anisotropies of the neighbouring phenyl groups. The results are used to estimate the degree of electron delocalization from the lone pair on phosphorus. The extent of delocalization depends on the internal motions and comparisons are made with phenylphosphine. The maximum possible screening of the para protons in phenylphosphine is calculated as 0.19 ppm for a conformation in which the lone pair on phosphorus is oriented perpendicular to the aromatic plane. The intramolecular rotational potentials then yield 0.029 ppm as the shielding of the para protons in triphenylphosphine due to electron delocalization, just as found for the CS2/C6D12 solution after correction for diamagnetic anisotropy fields.

1H nuclear magnetic resonance characterization of internal motions in the amorphous phase of low-density polyethylene

Polymer ◽  
1986 ◽  
Vol 27 (11) ◽  
pp. 1658-1664 ◽  
Author(s):  
D. Doskočilová ◽  
B. Schneider ◽  
J. Jakeš ◽  
P. Schmidt ◽  
J. Baldrian ◽  
...  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Amorphous Phase ◽  
Low Density Polyethylene ◽  
Low Density ◽  
Internal Motions ◽  
1H Nuclear Magnetic Resonance ◽  
Nuclear Magnetic

1H nuclear magnetic resonance and molecular orbital studies of the structure and internal rotations in ethylbenzene

1987 ◽  
Vol 65 (4) ◽  
pp. 873-877 ◽  
Author(s):  
Ted Schaefer ◽  
Glenn H. Penner ◽  
Rudy Sebastian
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Molecular Orbital ◽  
Proton Spin ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Orbital Theory ◽  
Spectral Parameters ◽  
Internal Barrier ◽  
Nuclear Magnetic

Rather extensive geometry-optimized computations at the STO-3G, 4-21G, 4-31G, and 6-31G levels of abinitio molecular orbital theory suggest that the fourfold component of the barrier to internal rotation about the Csp2—Csp3 bond in ethylbenzene amounts to about 20% of the twofold component. The 1H nuclear magnetic resonance spectral parameters, extracted by complete analyses of the spectra arising from the ten protons, are reported for ethylbenzene in acetone-d6, CCl4, CS2, and perfluoromethylcyclohexane solutions. The long-range proton–proton spin–spin coupling constants demonstrate that the internal barrier is insensitive to the polarity of the solvent, in contrast to polar solute molecules such as benzyl fluoride. The coupling constants do not support a dependence of the internal barrier on the internal pressure of the solvent.

Paramagnetic Ring Current in Cyclooctatetraene: Evidence from 1H Nuclear Magnetic Resonance Shifts of Fused Benzo Derivatives

1973 ◽  
Vol 51 (2) ◽  
pp. 177-182 ◽  
Author(s):  
G. W. Buchanan ◽  
A. R. McCarville
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Ring Current ◽  
Parent Compound ◽  
Electron Delocalization ◽  
Satellite Spectrum ◽  
1H Nuclear Magnetic Resonance ◽  
Related Compounds ◽  
Nuclear Magnetic

The 1H n.m.r. aromatic spectral regions of benzocyclooctatetraene and several related compounds have been analyzed using the LAOCOON 3 program. Assignments are based on the analysis of the 13C satellite spectrum of the parent compound. Results are interpreted in terms of appreciable π-electron delocalization in the 8π-electron eight-membered rings giving rise to measurable paramagnetic anisotropic effects.

Studies of specifically fluorinated carbohydrates. Part I. Nuclear magnetic resonance studies of hexopyranosyl fluoride derivatives

1969 ◽  
Vol 47 (1) ◽  
pp. 1-17 ◽  
Author(s):  
L. D. Hall ◽  
J. F. Manville ◽  
N. S. Bhacca
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Angular Dependence ◽  
Chemical Shifts ◽  
Relative Orientation ◽  
Coupling Constants ◽  
Pyranose Ring ◽  
Spectral Parameters ◽  
Magnetic Resonance Studies ◽  
Nuclear Magnetic

A detailed study has been made of both the 1H and 19F nuclear magnetic resonance (n.m.r.) spectra of a series of hexopyranosyl fluoride derivatives. Some of the 1H spectra were measured at 220 MHz. The 1H spectral parameters define both the configuration and the conformation of each of these derivatives. Study of the 19F n.m.r. parameters revealed several stereospecific dependencies. The 19F chemical shifts depend upon, (a) the orientation of the fluorine substituent with respect to the pyranose ring and, (b) the relative orientation of other substituents attached to the ring; for acetoxy substituents, these configurational dependencies appear to be additive. The vicinal19F–1H coupling constants exhibit a marked angular dependence for which Jtrans = ca. 24 Hz whilst Jgauche = 1.0 to 1.5 Hz for [Formula: see text] and 7.5 to 12.6 Hz for [Formula: see text] The geminal19F–1H couplings depend on the orientation of the substituent at C-2; when this substituent is equatorial JF,H is ca. 53.5 Hz and when it is axial the value is ca. 49 Hz.

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