Heteronuclear single-quantum multiple

HSQC HMQC Heteronuclear single-quantum/multiple-quantum correlation spectroscopy To elucidate structure of organic molecules To determine heteronuclear coupling connectivity... 

More recently, a gradient-enhanced heteronuclear single quantum multiple bond correlation (HSQMBC) experiment and its variants34,47,60-62 have been proposed for the measurement of heteronuclear coupling... 

Now a simple, general and pratical method is available for direct measurement of V(ch) coupling constants [73]. ID and 2D heteronuclear single quantum multiple bond correlation (HSQMBC) experiments are easily performed in a routine manner. These experiments are based on the evolution of heteronuclear single quantum coherence (SQC) in... 

HSQMBC = Heteronuclear Single Quantum Multiple Bond Correlation... 

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. 

Fig. 10.15. Pulse sequence for the multiplicity-edited gradient HSQC experiment. Heteronuclear single quantum coherence is created by the first INEPT step within the pulse sequence, followed by the evolution period, t . Following evolution, the heteronuclear single quantum coherence is reconverted to observable proton magnetization by the reverse INEPT step. The simultaneous 180° XH and 13C pulses flanked by the delays, A = l/2( 1 edits magnetization inverting signals for methylene resonances, while leaving methine and methyl signals with positive phase (Fig. 16A). Eliminating this pulse sequence element affords a heteronuclear shift correlation experiment in which all resonances have the same phase (Fig. 16B).

In order to carry out complete structural elucidation of unknown compounds (especially for complex molecules), the RF probe should enable a variety of heteronuclear NMR techniques to be performed. In particular, inverse detection H-15N and 1H-13C experiments such as heteronuclear multiple quantum coherence (HMQC) [29,30] and heteronuclear single quantum coherence (HSQC) [31] find almost ubiquitous application in myriad research environments. Although the microliter-scale probes described above feature both heteronuclear and homonuclear capabilities, no commerical product is... 

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... 

Heteronuclear multiple-quantum correlation Experiment for tailored correlation spectroscopy of H and H resonances in peptides and proteins Homonuclear Hartmann-Hahn spectroscopy Heteronuclear quadruple-quantum coherence Heteronuelear triple-quantum coherence Heteronuclear single-quantum coherence TOCSY sequences developed at the Indian Institute of Chemical Technology Insensitive nucleus enhancement by polarization transfer... 

Fourier transform or transformation heteronuclear chemical-shift correlation heteronuclear multiple bond correlation heteronuclear multiple quantum correlation heteronuclear single quantum correlation... 

The assignment of heteronuclei generally requires acquisition of a heteronuclear single quantum coherence (HSQC) experiment and a heteronuclear multiple bond correlation (HMBC) experiment, and these are described in more detail below. 

---