High-field spectra

Angular Dependence of the Effect of Quadrupole Interaction in High-Field Spectra... 

The constants / and g are functions of the magnetic susceptibility of the molecule when the magnetic field is aligned perpendicular or parallel to the intemuclear axis. They are very small in magnitude and were only included in the analysis of the high field spectra. We will discuss these quantities at length in section 8.2.2. They are closely related to the shielding parameter [Pg.380]

Sideband analysis Resolution of bridgehead, non-bridgehead and tertiary aromatic carbons Relative intensities of sidebands used in high field spectra... 

Another, perhaps clearer indication for isostructural character is given by solid-state,, 3C cross-polarization magic angle-spinning (CPMAS) NMR. A comparison of the high-field spectra revealed strong similarities for the decaphenylgermanium and tin compounds (the amorphous lead complex produced broader lines) (120). 

The motivation for this intense activity is the resolution enhancement available from higher Larmor fields, which enables small g-tensor splittings to be readily observed (Earle et al., 1994). For systems with large zero field splittings (Lynch et al., 1993), high-field spectra can be much simpler to analyze than X-band spectra, which increases the reliability and eases the interpretation of the data. In the study of fluid media (Earle et al., 1993), the increased importance of the g-tensor contributions vis-a-vis the hyperfine tensor contributions (e.g., for nitroxide spin labels) gives information that is complementary to lower-field studies. These concepts are discussed more fully elsewhere (Lebedev, 1990 Budil et al., 1989), and we refer the reader to the references for a more complete discussion. 

In Fig. 2 is the spectrum of the same compound run on a 250-MHz spectrometer. The chemical shift of the triplet is now 457.5 Hz from the TMS peak. But, expressed in dimensionless d units, it is still 1.83 ppm according to the above equation. The distance between individual peaks in the triplet and the quartet is still 8 Hz because the size of the coupling constant does not change with magnetic field strength. High field spectra like this one are easier to analyze than low field (60 MHz) spectra because the amount of peak overlap in complex molecules is much less. In this text you will find both high and low field spectra. 

Chemical Shift Reagents High-Field Spectra 323... 

CHEMICAL SHIFT REAGENTS HIGH-FIELD SPECTRA... 

A number of ingenious pulse techniques have been devised to eliminate sidebands from high-field spectra so that normal CP/MAS spectra are generated. These are referred to as PASS (Phase Alternated Sideband Suppression) and TOSS (TOtal Sideband Suppression) techniques. An example of the use of TOSS to suppress sidebands from the aromatic carbons in Illinois No. 6 coal is shown in Fig. 3. Two different spinning rates were... 

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