Scale factors chemical shift

Several methods have been developed to determine the chemical shift anisotropies in the presence of small and large quadrupolar broadenings, including lineshape analysis of CT or CT plus ST spectra measured under static, MAS, or high-resolution conditions [206-210]. These methods allow for determination of the quadrupolar parameters (Cq, i)q) and chemical shift parameters (dcs, //cs> <5CT), as well as the relative orientation of the quadrupolar and chemical shift tensors. In this context, the MQMAS experiment can be useful, as it scales the CSA by a factor of p in the isotropic dimension, allowing for determination of chemical shift parameters from the spinning sideband manifold [211],... 

The second term leads to a vestigal powder pattern, scaled down by J2e. The rule of thumb becomes to reduce chemical shift anisotropy by a factor of 100, set the angle to within about 1/2 degree. 

The combined strategy of calculating the 19F chemical shifts has been studied for fluorobenzenes [62] in several solvents. Here crw has been found to be the dominant contribution to the total solvent-induced change of chemical shift the authors have neglected the solvent magnetic anisotropy contribution cra which is related to the short-range interactions. To obtain the agreement with the experimental data, the term [Pg.137]

The use of a secondary reference and/or employment of external referencing is a result of some practical considerations. Aspects considered range from principal factors like sample solubility, boiling point or signal overlap to trivial matters of convenience such as routine or tradition in a laboratory. In practice, the chemical shift S, measured relative to a secondary reference as an internal reference, is converted into the 6 scale according to the equation 2... 

Figure 11.3 shows the downfield portion of the spectrum of sucrose (gl doublet, /HH = 3.8 Hz) with normal vertical scaling and with the vertical scale increased by a factor of 100 to show the 13C satellites. The satellites show the same doublet 7rh coupling observed in the 12C-bound proton signal (7=3.8 Hz), with an additional 169.6 Hz coupling to the 13C nucleus (Vch)- The peak height is roughly half (actually half of 1% because the vertical scale is 100 x) of the central peak because they are part of a doublet with concentration about 1% of the concentration of the 12C species. If you look closely you will see that the center of the double doublet is not exactly the same chemical shift... 

The 8 scale is clearly dimensionless, but with the factor of 106, 8 has the units of parts per million (ppm) and a value should be stated, for example, as 8 = 4.13 ppm. Column headings in tables may be expressed as 8/ppm. In some instances when small differences in chemical shifts are being discussed, it may be more convenient to use a multiplicative factor of 109, with the units of parts per billion (ppb). 

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