13C-Satellite peaks

The commonly used solvents for reversed-phase HPLC separations are methanol and acetonitrile. Both of these solvents give rise to a singlet resonance in the H NMR spectrum which can be suppressed easily. However, the 13C satellite peaks, caused by the one-bond H-13C spin couplings from the 1.1 % of molecules with the naturally abundant 13C isotope at the methyl carbon, remain following suppression of the main peak and are often much larger than the signals for the analytes, and thus these must also be suppressed. 

The H NMR spectrum of 1,3-dioxolane was first reported in 1959, the coupling constants being derived using the 13C satellite peaks (59MI43000). Other early work on 2-substituted... 

Two final interesting points relating to 13C satellites... Whilst they are generally, evenly spaced on either side of the major peak, they do not have to be exactly symmetrically disposed about it. It is... 

Other even more cunning methods have been devised to suppress the water signal in samples that have a large water content (e.g., bio-fluid samples) such as the WET and the WATERGATE pulse sequences. Other sequences have been devised to cope with signals from carbon-bound hydrogens. Some of these actually collapse the 13C satellites into the main 12C peak prior to suppression. Such a sequence would be useful if you were forced to acquire a spectrum in a nondeuterated solvent. 

Using the atomic weights given in Table 4.2, calculate the mass spectral resolution required to separate the molecular ion of atomic composition C35H48N8O11S from the isotopic peak containing one 13C atom and carry out a similar calculation for the ion of composition C284H432N8407gS7 and its single 13C satellite. 

Is not known Thus it seems reasonable that one or more of the satellite peaks of the 1,4 peaks might arise from 1,2 methylene carbons as shown in VII and VIII. It is not certain what the multiple peaks near 35 ppm represent, but they probably arise from C-13c spin-spin coupling in oligomers with a DP of 2 or more The sharp peak at 29.70 is due to the methyl carbons of the reacted t-butyl group ... 

A number of other features apparent in the toluene proton spectrum are worthy of note at this stage. Each absorption is accompanied by a number of small satellite peaks equally spaced on either side of the main absorptions. These may be spinning side-bands or 13C satellites (p. 342). The spinning side-bands are caused by inhomogeneities in the magnetic field and in the sample tube. They... 

In the upper spectrum taken from a LC-NMR run (Figure 7.2.5(a)), despite solvent suppression there are large remaining solvent signals, i.e. water at 3.7 ppm and acetonitrile with 13C satellites at 2.1 ppm. In cases where the sample peaks lie under the solvent signals, structure elucidation is difficult or... 

Magic angle spinning (MAS) NMR brings the power of H NMR to solid-phase chemistry [2,25], A simple MAS spectrum, that of the reaction product of succinic anhydride and TentaGel S NH2, is shown in Fig. 2. Presaturation of the PEG resonance at 3.6 ppm is critical to spectral quality. The complex peaks from 3.4 to 3.9 ppm are due to residual PEG, 13C satellites and the terminal CH2 of the PEG chain. The characteristic doubling of the solution-phase CDC1, and TMS resonances can be seen. 

The HMBC for ipsenol (Figure 5.14) looks like the HMQC for ipsenol with two obvious differences there are considerably more correlations and the one bond correlations (HMQC) are gone. (The spectrum is broken into five sections so that there is sufficient resolution to see all of the correlations.) Interpretation for ipsenol is straightforward. But first, let us note a common artifact 13C satellites of intense proton peaks,... 

Each of these gives rise to an AB pattern due to 13C-13C splitting ( Jcc for the first two and 2JCC for the third species). These additional 13C signals appear as weak satellite peaks (0.55% of the main peak) around the main peaks from the first three species, and because signal-to-noise ratios are typically much less than 200 for 13C spectra, these signals will be buried in the noise. Finally, there is one isotopomer with three 13C nuclei ... 

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... 

In view of all this, you may ask why we don t apparendy see couplings between 13C and H in either carbon or proton spectra. In proton spectra we don t see coupling to 13C because of the low abundance (1.1%) of 13C. Most protons are bonded to 12C only 1.1% of protons are bonded to 13C. If you look closely at proton spectra with very flat baselines, you may see small peaks either side of strong peaks at about 0.5% peak height. These are the 13C satellites for those protons that are bonded to 13C atoms. 

Interpretation for ipsenol is straightforward. But first, let us note a common artifact 13C satellites of intense proton peaks especially methyl groups. If we trace... 

The 13C labels allow for use of 13C NMR in which the peaks containing the 13C label enrichment show satellites corresponding to a 1JCc coupling ( 30 Hz). The distribution pattern of 13C labels found was more complicated than one single pathway and pointed toward both pelletierine and cocaine-derived alkaloid pathways, both which incorporate two acetate units Hemscheidt T, Spenser ID (1993) J Am Chem Soc 115 3020... 

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