Carbon satellite

HPLC requires much larger amounts of solvents, so that deuterated materials are too expensive instead we work with undeuterated HPLC quality solvents, the proton signals from which are suppressed using the so-called WET sequence, which also suppress the carbon-13 satellites of the solvent signals. 

So far, we have not considered the so-called longitudinal two-spin order, represented by the product operator9 2J ff, a quantity related to the polarization of nuclei A and B. This spin state can be created in different ways. The easiest way is probably to let the system evolve under the sole Jab coupling so as to obtain an antiphase doublet, for instance the B antiphase doublet represented by 2//Vf (corresponding to the two proton-carbon-13 satellites in an antiphase configuration). 

Fig. 3. Long range and one-bond carbon-13 satellite spectrum of a 5% w/w solution of ethanediol in D2O at 94°C. 16 transients were measured on a Varian Associates Unity 500 spectrometer using the sequence of fig. 1, with 2.5 s presaturation, a t value of 100 ms, spin lock pulses of 450 ps, no homospoil pulse, and no homodecoupling during acquisition.

In principle we could deconvolute the experimental spectrum with the instrumental lineshape, if that were known, to recover the true spectrum. In our example we have some good experimental evidence as to the form of the instrumental lineshape since the acetone signal is (apart from small carbon-13 satellites) a singlet, its experimental shape is just the instrumental lineshape convoluted by a Lorentzian of width l/(7rr2 ), where is the spin-spin relaxation time of the acetone protons. How can we use this experimental evidence to correct the imperfect experimental spectrum The simplest way to deconvolute one function fi uj) by another f2 ( ) is to Fourier transform the ratio of their inverse Fourier transforms ... 

Figure 11 Carbon-13 satellites due to scalar coupling /(, Li) in the 58.88 MHz Li NMR spectrum of isopropyllithium (1.4 M in pentane at — 53 Q with Li signals of the hexamer (H) and tetramer (T) external reference 0.1 M LiBr in THF...

Figure 15 Carbon-13 satellites due to scalar couplmg /( C, Li) m the Li spwtrum the tetramer (T) and hexamer (H) of isopropyllithium...

Figure 3.27. Dynamic range and the detection of small signals in the presence of large ones. As the digitiser resolution and hence its dynamic range are reduced, the carbon-13 satellites of the parent proton resonance become masked by noise until they are barely discernible with only 6-bit resolution (all other acquisition parameters were identical for each spectrum). The increased noise is digitisation or quantisation noise (see text below).

Figure5.75. The ID INADEQUATE experiment (b) selects for the carbon-13 satellites in the conventional carbon-13 spectra (a) and provides a means of measuring carbon-carbon coupling constants. Some residual parent resonances from lone C centres remain in (b).

F re 6.5. Selection of satellite resonances in the HMQC experiment through phase-cycling. The phase of the carbon-13 satellites can be inverted by inverting the phase of the first 90° carbon pulse (a vs b). Subtraction of these two data sets by inverting the receiver phase also, cancels the parent H- C resonance but reinforces the satellites (c). 

Possibly one of the most difficult tasks each year is that of writing the General Review of Proton Magnetic Resonance because of the enormous number of papers dealing with such a wide variety of topics. However, I hope the more specialized chapters dealing with specific topics of proton NMR will help to broaden these aspects. The advent of sensitivity enhancement devices has clearly spurred the spectro-scopist to make greater use of carbon-13 satellite spectra. The numerous references, to these satellite spectra, contained in this Volume will undoubtedly encourage chemists to make use of the information contained therein. 

Figure 6. Ultrahigh resolution FT-ICR mass spectra. Each transient was acquired for 1.02 sec and had 250 msec relaxation time. The 867 peak in (e) is the carbon-13 satellite of the 866 peak, (f) is a plot of the mass resolution versus ion mass for the spectra of (a)-(e).

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