Heteronuclear single-bond correlations proton detected

Figure 15.1. (A) COSY, (B) TOCSY, (C) 1H-1T HSQC or HMQC, (D) dl- Y HMBC, for 4-oxopentanal. For clarity, only key assignments have been given as an example. Note that the double-ended arrows indicate how to interpret the spectra. In the case of COSY and TOCSY the information is represented as cross-peaks that are symmetrically oriented with respect to the central diagonal. In the single-bond correlation (HSQC/HMQC) a cross-peak represents in one dimension the carbon chemical shift and in the other dimension the proton chemical shift. Note there is no diagonal in heteronuclear NMR experiments. In the HMBC, lines are drawn vertically to connect the cross-peaks. In HMBC 2-4 bonds, H-13C correlations are often observed. Note that the 4-bond correlation is less common in NMR but has been included here as an example, and 1-bond correlation is commonly filtered from the HMBC experiment to improve detection limits for the weaker 2-4 bond correlations.

The heteronuclear multiple-quantum correlation (HMQC) experiment is one of the two commonly employed proton-detected single-bond correlation experiments. Although this was suggested many years ago [1,2], the experiment lacked widespread use until a scheme was presented [3] that was able to overcome the technical difficulties associated with proton observation described above. Since then, and particularly since the advent of PFGs, the technique has come to dominate organic NMR spectroscopy. 

Heteronuclear single-quantum correlation (HSQC) permits to obtain a 2D heteronuclear chemical shift correlation map between directly bonded H and X-heteronuclei (commonly and N). It is widely used because it is based on proton-detection, offering high sensitivity when compared with the conventional carbon-detected 2D HETCOR experiment. Similar results are obtained using the 2D HMQC experiment [77],... 

Proton-detected two-dimensional (2D) NMR experiments, essentially based on two difierent pulse schemes referred to as heteronuclear single-quantum correlation (HSQC) [1] and heteronuclear multiple-quantum correlation (HMQC) [2], have been key NMR tools during many years for chemists and biochemists to provide valuable structural information on H- C (and H- N) chemical bonds in a molecule. Nowadays, these experiments are usually performed in a complete automation mode in both data acquisition and processing steps, practically without any need for direct user intervention. The resulting 2D maps are very simple to analyze and to interpret, even for non-experienced NMR users, typically displaying well-dispersed cross-peaks that correlate (direct F2 dimension) and (indi-... 

HC HMQC (heteronuclear multiple quantum coherence) and HC HSQC (heteronuclear single quantum coherence) are the acronyms of the pulse sequences used for inverse carbon-proton shift correlations. These sensitive inverse experiments detect one-bond carbon-proton connectivities within some minutes instead of some hours as required for CH COSY as demonstrated by an HC HSQC experiment with a-pinene in Fig. 2.15. 

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