Heteronuclear multiple-bond coherence

Two-dimensional C//correlations such as C//COSY or HC HMQC and HSQC provide the Jqh connectivities, and thereby apply only to those C atoms which are linked to H and not to non-protonated C atoms. Modifications of these techniques, also applicable to quaternary C atoms, are those which are adjusted to the smaller Jqh and Jqh couplings (2-25 Hz, Tables 2.8 and 2.9) Experiments that probe these couplings include the CH COLOC (correlation via long range couplings) with carbon-13 detection (Fig. 2.16) and HC HMBC (heteronuclear multiple bond coherence) with the much more sensitive proton detection (Fig. 2.17)... 

NMR data are heteronuclear multiple quantum coherence and heteronuclear multiple bond coherence readouts the carbon atoms at sites of glycosylation are given in bold. 

A modification of the HMQC referred to as the HMBC (Heteronuclear Multiple Bond Coherence) experiment can be optimized for transfer through multiple bonds based on the value of the multiple bond couplings, which is typically about 8 Hz for a three-bond coupling. The HMBC spectrum of dutasteride shown in Fig. 9 illustrates the utility of this experiment for assigning quaternary carbons, connecting isolated spin systems (e.g., Hig and Hig) to other spin systems in the molecule, and confirming assignments made from the COSY and HMQC spectra. 

H homonuclear correlation spectroscopy (COSY). The connection between the benzyltetraisoquinoline and pavine moieties in 66 was located at C-10 and C-7 through an ether bridge as a result of the unambiguous assignments of H and 13C NMR signals by the heteronuclear multiple-bond quantum coherence (HMQC) and heteronuclear multiple-bond coherence (HMBC) NMR techniques. The EIMS of 66 confirmed the presence of a hydroxybenzyl moiety due to the observed complementary peaks at m/z 545 and 107 [11]. Furthermore, the structure of 66 was substantiated by the formation of herveline C (68) after 66 was treated with diazomethane in ethyl ether solution overnight [11]. 

For the HMQC described above, we wanted an experiment that eliminated long-range (i.e., two and three bond) proton-carbon couplings while preserving the directly attached (i.e., one-bond) couplings, which we correlated in a 2-D experiment. The HMBC (Heteronuclear Multiple Bond Coherence) experiment, on the other hand, which is also proton detected, capitalizes... 

But Rh, Ag, or Pt exhibit chemical shift differences - preferentially determined by heteronuclear multiple bond coherence (HMBC) spectra-as well as J-coupling in the form of satellites in the spectra of the sensitive nuclei [12]. However, some paramagnetic nuclei increase the magnetic relaxation and increase the line broadening. 

Thiophene A and thiophene A diol are the major polyacetylenes isolated from the hairy root of Ambrosia maritima L. (Asteraceae) [293]. Their chemical structures were determined by mass spectroscopy and using DEPT 135, HMQC (heteronuclear multiple quantum coherence), and HMBC (heteronuclear multiple bond coherence) NMR experiments (Figure 5.79). 

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