Electron delocalization in paramagnetic metallocenes. I. Nuclear magnetic resonance contact shifts

1969 ◽  
Vol 91 (6) ◽  
pp. 1361-1370 ◽  
Author(s):  
Michael F. Rettig ◽  
Russell S. Drago
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Electron Delocalization ◽  
Nuclear Magnetic

Electron delocalization in mixed-valence biferrocenium salts: nuclear magnetic resonance contact shift studies

1990 ◽  
Vol 29 (1) ◽  
pp. 80-84 ◽  
Author(s):  
Teng Yuan Dong ◽  
Ming Yhu Hwang ◽  
Tsui Ling Hsu ◽  
Chi Chang Schei ◽  
Show Kei Yeh
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Mixed Valence ◽  
Electron Delocalization ◽  
Contact Shift ◽  
Nuclear Magnetic

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.

An emerging technology: Nuclear magnetic resonance microscopy

1988 ◽  
Vol 46 ◽  
pp. 1000-1001
Author(s):  
M.J. Hennessy ◽  
E. Kwok
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Relaxation Times ◽  
Basic Research ◽  
Local Environment ◽  
Magnetic Resonance Images ◽  
Nmr Microscopy ◽  
Mri Scans ◽  
Temperature Relaxation ◽  
Nuclear Magnetic

Much progress in nuclear magnetic resonance microscope has been made in the last few years as a result of improved instrumentation and techniques being made available through basic research in magnetic resonance imaging (MRI) technologies for medicine. Nuclear magnetic resonance (NMR) was first observed in the hydrogen nucleus in water by Bloch, Purcell and Pound over 40 years ago. Today, in medicine, virtually all commercial MRI scans are made of water bound in tissue. This is also true for NMR microscopy, which has focussed mainly on biological applications. The reason water is the favored molecule for NMR is because water is,the most abundant molecule in biology. It is also the most NMR sensitive having the largest nuclear magnetic moment and having reasonable room temperature relaxation times (from 10 ms to 3 sec). The contrast seen in magnetic resonance images is due mostly to distribution of water relaxation times in sample which are extremely sensitive to the local environment.

Nuclear magnetic resonance microscopy

1989 ◽  
Vol 47 ◽  
pp. 828-829
Author(s):  
Paul C. Lauterbur
Keyword(s):  
Magnetic Field ◽  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Magnetic Fields ◽  
Signal To Noise ◽  
Field Gradients ◽  
Useful Signal ◽  
Magnetic Field Gradients ◽  
Observation Times ◽  
Nuclear Magnetic

Nuclear magnetic resonance imaging can reach microscopic resolution, as was noted many years ago, but the first serious attempt to explore the limits of the possibilities was made by Hedges. Resolution is ultimately limited under most circumstances by the signal-to-noise ratio, which is greater for small radio receiver coils, high magnetic fields and long observation times. The strongest signals in biological applications are obtained from water protons; for the usual magnetic fields used in NMR experiments (2-14 tesla), receiver coils of one to several millimeters in diameter, and observation times of a number of minutes, the volume resolution will be limited to a few hundred or thousand cubic micrometers. The proportions of voxels may be freely chosen within wide limits by varying the details of the imaging procedure. For isotropic resolution, therefore, objects of the order of (10μm) may be distinguished.Because the spatial coordinates are encoded by magnetic field gradients, the NMR resonance frequency differences, which determine the potential spatial resolution, may be made very large. As noted above, however, the corresponding volumes may become too small to give useful signal-to-noise ratios. In the presence of magnetic field gradients there will also be a loss of signal strength and resolution because molecular diffusion causes the coherence of the NMR signal to decay more rapidly than it otherwise would. This phenomenon is especially important in microscopic imaging.

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