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.

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.

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