Couplings, heteronuclear

SWi, which in turn is related to the homonuclear or heteronuclear coupling constants. In homonuclear 2D spectra, the transmitter offset frequency is kept at the center of (i.e., at = 0) and F domains. In heteronuclear-shift-correlated spectra, the decoupler offset frequency is kept at the center (Fi = 0) of thei i domain, with the domain corresponding to the invisible or decoupled nucleus. 

The most downfield cross-peaks, V-Y, are due to heteronuclear couplings of the aromadc or vinylic protons and carbons. For instance, cross-peak Y represents heteronuclear interaction between the C-1 vinylic proton (8 5.56) and a carbon resonating at 8 134.0 (C-1). The downfield cross-peaks, V and W, are due to the heteronuclear correlations of the ortho and meta protons (8 7.34 and 7.71) in the aromatic moiety with the carbons resonating at 8 128.3 and 126.9, respectively. The remaining cross-peak X is due to the one-bond correlation of the C-4 aromatic proton (8 7.42) with the C-4 carbon appearing at 8 131.4. The cross-peak U displays direct H/ C connectivity between the carbon at 8 77.9 (C-6) and C-6 methine proton (8 4.70). The crosspeak T is due to the one-bond heteronuclear correlation of carbon... 

Nolls, P., Parella, T. Spin-edited 2D HSQC-TOCSY experiments for the measurement of homonuclear and heteronuclear coupling constants application to carbohydrates and peptides. /. Magn. Reson. 2005, 176, 15-26. 

As we have already pointed out in the section dealing with heteronuclear coupling that it is not always necessary to confirm the presence of a particular hetero atom by acquiring the NMR spectrum of that nucleus. More often than not, the hetero atom will have a clear signature in the proton or carbon spectrum. Fluorine and phosphorus are both examples of nuclei that couple to protons over two, three, four and even more bonds. 

During the delay A, the proton coherence associated with long-range heteronuclear couplings is fully converted into anti-phase (AP) magnetization. The second 90° pulse applied on the 13C channel converts this AP magnetization into heteronuclear multiple quantum coherences (2HxCy). 

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