Chemical shift reference compounds

Only Cq( Ti) values specifically reported or calculated by the authors are listed. In line with their different values of Q [43], Cq( Ti) = 1.222[Cq( Ti)j. chemical shift reference compound was provided. 

Tetramethylsilane (TMS) is the most commonly used chemical shift reference compound for H and C NMR. In both types of spectra TMS gives a single sharp resonance at lower frequency than most other proton or carbon resonances. The TMS is usually added to the sample solution as an internal reference. The accepted sign convention is for chemical shifts to high and low frequency of the reference peak to be positive and negative, respectively. Figure 9 shows the 250 MHz H spectrum of methyl acetate... 

The scatter plot in Figure 1 gives correlation of the quadrupole splitting and the chemical shift (at 78°K.) for several tin compounds (5, 9, 16) using white tin (beta) for a chemical shift reference. The various sources and their linewidths are also shown. 

Compound Solvent Coordination Status Oligomer Name Chemical Shift Reference... 

Theoretically, any external standard may be used, provided that it is clearly defined, and that precise data are available which make possible the accurate recalculation of nitrogen chemical shifts referred to other standards. Practically, there are limitations concerning the concentration of nitrogen nuclei in the reference compound, the sensitivity of its nitrogen chemical shift to concentration and solvent effects in the case of solutions, effects due to possible impurities, nuclear Overhauser effects on the resonance upon proton decoupling etc. 

Table 1. Se chemical shifts of compounds used as references, relative to Me2Se in CDCI3 (60% v/v) ...

When preparing a sample it is common practice to add a suitable compound to act as an internal chemical shift reference in the spectrum, and the selection of this must be suitable for the analyte and solvent. In proton and carbon NMR, the reference used in organic solvents is tetramethylsilane (TMS, 0.0 ppm) which has a number of favourable properties it has a sharp 12-proton singlet resonance that falls conveniently to one end of the spectrum, it is volatile so can be readily removed and it is chemically inert. In a few cases this material may be unsuitable such as in the study of silanes or cyclopropanes. For routine... 

Table 2.1. Chemical shift references for biological phosphorus compounds in solution nuclear magnetic resonance spectroscopy. Bold type indicates general peak shift ranges regular type indicates specific chemical shift assignments.

Table 2.2. Chemical shift references for phosphorus compounds from solid-state nuclear magnetic ...

Chemical Shifts. The " Si resonance of TMS is the usual chemical shift reference. Si chemical shifts cover a range of ca. 400 ppm. The large dispersion arising from structural effects makes Si NMR a valuable tool for molecular structure determination. The nature of the atoms directly bonded to silicon is of particular importance. Table 8 lists chemical shifts for a series of compounds SiX Meo . Si NMR has proved to be an ideal tool for structure determination of poly-siloxane macromolecules. 

As mentioned in Section 2.3.1, the almost universally adopted primary reference for chemical shifts in NMR spectra is the compound tetramethylsilane (TMS). Incidentally, TMS is also employed as the primary chemical shift reference in H and Si NMR [18]. Some old reports give chemical shifts relative to benzene or carbon disulfide, but the use of the TMS resonance as the zero chemical shift mark is now commonplace. Unfortunately, TMS is highly volatile, toxic, and flammable, which makes problematic its use as a direct reference sample. A simple alternative is to use another sample with a known spectrum as an external and secondary reference. In the case of solid-state NMR there are many known secondary standards, such as adamantane (higher-frequency peak at 38.6 ppm), hexamethylbenzene (higher-frequency peak at 132.2 ppm), and glycine (higher-frequency peak at 176 ppm) [4,15,98]. 

In F NMR experiments, a problem exists in the choice of chemical shift reference since the reactivity of some fluorine compounds has often precluded their use as internal standard. However, the standard... 

Table 7.47 Proton Chemical Shifts of Reference Compounds 7.98...

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