Heteronuclear shift-correlation long-range experiments

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. 

LONG-RANGE HETERONUCLEAR SHIFT CORRELATION HMBC AND RELATED EXPERIMENTS... 

To provide the means of sampling a wider range of potential long-range heteronuclear coupling constants, an alternative version of this heteronuclear shift correlation experiment is called the accordion-optimized HMBC, or ACCORD-HMBC [50]. Additional modifications of this experiment are also available [51]. 

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. 

The development of gradient-enhanced heteronuclear shift correlation experiments in the early 1990s heralded a major improvement in the applicability of these experiments for H- N direct and long-range heteronuclear shift correlation... 

The available accordion-optimized long-range heteronuclear shift correlation experiments were surveyed in a recent chapter. No novel accordion-optimized methods have been reported, but following the author s initial report on the advantages of using the IMPEACH-MBC sequence for long-range studies, Kline and Cheatham have... 

Fig. 4. Any of the long-range experiments designed to differentiate between V and J n = 3, 4), although developed for heteronuclear shift correlation applications, can also be applied...

Long-range heteronuclear shift correlation. Russell et al have demonstrated the viability of F-detected long-range IMPEACH-MBC experiments... 

New long-range heteronuclear shift correlation experiments 48... 

A period of intense research effort devoted to the development of new long-range heteronucieus-detected heteronuclear shift correlation experiments followed Reynolds " first demonstration of the feasibility of performing long-range heteronuclear shift correlation experiments. These methods have been reviewed" and only a couple of salient points will be discussed here. 

---