Heteronuclear single-bond correlation spectroscopy

There are two techniques in widespread use that provide single-bond heteronuclear shift correlations, known colloquially as HMQC and HSQC. The correlation data provided by these two methods are essentially equivalent, the methods differing only in finer details, which, for routine spectroscopy, are often of little consequence. As such, both methods are ubiquitous throughout the chemical literature and hence will be described in the sections that follow. Historically, the HMQC experiment has been favoured by the chemical community and HSQC by biological spectroscopists. This is, at least in part, due to the manner in which the early experiments were presented, viz HMQC for H- C correlations in small molecules and HSQC for correlations in proteins. At a practical level, the HMQC experiment tends 

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Other strategies that show great promise in reducing NMR acquisition time utilise methods to obtain multiple sets of data from one experiment through a concept known as time-shared evolution. An example of this process that should find utility in natural products elucidation was demonstrated by a pulse sequence called CN-HMBC.93 Traditionally, a separate 13C-HMBC and 15N-HMBC were acquired independently. However, the CN-HMBC allows both 13C- and 15N-HMBC spectra to be obtained simultaneously. By acquiring both data sets simultaneously, an effective 50% time reduction can be achieved.93 This approach has also been demonstrated for a sensitivity-enhanced 2D HSQC-TOCSY (heteronuclear multiple bond correlation total correlation spectroscopy) and HSQMBC (heteronuclear single quantum... 

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. 

The main emphasis of current carbohydrate structural analysis is the applicability of modern multi-dimensional NMR for solving the two crucial problems in complex carbohydrate structural analysis, namely, the elucidation of the sequence of glycosyl residues and the solution conformation and dynamics of a carbohydrate (150). Techniques include 2D Total Correlation Spectroscopy (TOCSY), Nuclear Overhauser effect spectroscopy (NOESY), rotational nuclear Overhauser effect spectroscopy (ROES Y),hetero-nuclear single quantum coherence (HSQC), heteronuclear multiple quantum correlation (HMQC), heteronuclear multiple bond correlation (HMBC), and (pseudo) 3D and 4D extensions. 

M. Takasaki, K. Kimura, Y. Nakagawa, N. Sato, B. Bae, K. Miyatake, M. Watanabe, Complete NMR assignment of a stdfonated aromatic block copolymer via heter-onuclear single-quantum correlation, heteronuclear multiple-bond correlation and heteronuclear single-quantum correlation total correlation spectroscopy, Polym. J. 44 (2012) 845-849. 

FIGURE 8.2. Flowchart for structure elucidation of purified compounds. DEPT Distortionless Enhancement by Polarization Transfer, HMBC Heteronuclear Multiple Bond Correlation, HSQC Heteronuclear Single Quantum Coherence, HMQC Heteronuclear Multiple Quantum Correlation, DQF-CQSY Double Quantum Filtered Correlated Spectroscopy and NOSEY Nuclear Overhauser effect spectroscopy. 

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