Long-range C/H correlation

Finally, a 2D COLOQ experiment showed the following long range C-H correlations ... 

DEPT, H-H COSY, TOCSY, short range C-H chemical shift correlation and long range C-H chemical shift correlation experiments were performed on Bruker AMX 360 and AM400 instruments using acetone-d6 as solvent. C-H chemical shift correlation experiments were carried out with inverse detection. Standard pulse sequence programs provided with the instruments were used for all 2-D experiments. 

The partial long range C-H chemical shift correlation spectrum presented in figure 3 shows signals from the aliphatic side chains of the trimeric compound. This 2-D NMR experiment provides information about the H-C connection 2 to 3 bonds away from the carbon (coupling constants less than 20 Hz). For example, Ha shows... 

Figure 3. Partial long range C-H chemical shift correlation NMR spectrum of compound 20.

The modified heteronuclear shift-correlation experiment described by Bauer et al,54 has the advantage of giving 2D-spectra with proton shifts in the F, dimension and long-range C,H splittings. However, its overall sensitivity is low because of relaxation during relatively long delays, and the resolution obtained is only to the nearest Hertz. 

SALP I ester carbonyls Long-range C/H shift correlation... 

In homonudear shift-correlation experiments like COSY we were concerned with the correlation of chemical shifts between nuclei of the same nuclear species, e.g., H with H. In heteronuclear shift-correlation experiments, however, the chemical shifts of nuclei belonging to different nuclear species are determined (e.g., H with C). These may be one-bond chemical shift correlations, e.g., between directly bound H and C nuclei, or they may be long-range chemical shift correlations, in which the interactions... 

The HMBC spectrum of vasicinone along with the H-NMR assignments are shown. Determine the H/ C long-range heteronuclear shift correlations based on the HMBC experiment, and explain how HMBC correlations are useful in chemical shift assignments of nonprotonated quaternary carbons. 

The HMBC spectrum of vasicinone displays long-range heteronuclear shift correlations between the various H/ C nuclei. These correlations are very helpful to determine the C-NMR chemical shifts of quaternary carbons and allow the interlinking of the different substructures obtained. 

Fig. 28 C, H correlation spectrum for compound 1 (set for long-range coupling, 400 MHz, 5% in CDC13, measurement time 18 min, inverse detection)... 

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