HMQC heteronuclear multiple quantum

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. 

HMQC Heteronuclear multiple quantum coherence, e.g. inverse CH correlation via one-bond carbon proton-coupling, same format and information as described for ( C detected) CH COSY but much more sensitive (therefore less time-consuming) because of H detection... 

C-NMR, COSY, HMQC (heteronuclear multiple quantum coherence), and HMBC (heteronuclear multiple bond correlation).48 Furthermore, the structure of trimer was confirmed by X-ray crystallography.48 The incorporation of 13C into the indole 3a position proved valuable in these structural determinations and in documenting the ene-imine intermediate. For example, the presence of a trimer was readily determined from its 13C-NMR spectrum (Fig. 7.7). 

To be fair, we must point out that this type of experiment is extremely sensitive to the parameters chosen. Various pulse sequences are available, including the original COLOC (Correlation by means of Long range Coupling) as well as experiments variously referred to as HMBC (Heteronuclear Multiple-Bond Correlation) and HMQC (Heteronuclear Multiple-Quantum Correlation). Depending on the parameters chosen, it is often not possible to suppress correlations due to one-bond coupling ... 

In addition to well-resolved one-dimensional (ID) 1H and 13C spectra, which are usually sufficient for monitoring synthetic steps, HR-MAS techniques can be applied to two-dimensional (2D) homonuclear and heteronuclear experiments, which allow a wealth of structural information to be obtained. H,13C HMQC (heteronuclear multiple quantum coherence) spectra are particularly useful in the analysis of solid support-bound oligosaccharides, since the anomeric protons exhibit characteristic resonances. Such a spectrum of a polymer-bound trisaccharide glycal is shown in Figure 8.4. 

Because of the favorable cross-peak multiplet fine-structure, the HSQC experiment offers superior spectral resolution over the HMQC (heteronuclear multiple quantum coherence) experiment [13, 14], On the other hand, the HMQC experiment works with fewer pulses and is thus less prone to pulse imperfections. The real advantage of the HSQC experiment is for measurements of samples at natural isotopic abundance and without the use of pulsed field gradients, since the HSQC experiment lends itself to purging with a spin-lock pulse. Spin-lock purging in the HMQC experiment... 

The structural assignment of the trithiepines 44-46 has been performed using H, 13C, heteronuclear multiple bond correlation (HMQC), heteronuclear multiple quantum correlation (HMBC), and variable-temperature NMR spectroscopic data. The 60MHz H NMR spectrum of trithiepine 44 exhibits a broad singlet at 3.05 ppm in CDC13, whereas a narrow ABCD multiplet was observed for all of the protons in a 300 MHz spectrum. The two 13C NMR signals at... 

Historically, the HMQC (Heteronuclear Multiple Quantum Correlation) experiment was preceded by... 

HMQC (heteronuclear multiple quantum correlation) is a variant of the HSQC spectrum that gives essentially the same results with a slightly different strategy (Fig. B. 14). Instead of converting antiphase SQC into antiphase 13C SQC, a single 90° pulse on 13C alone converts it into multiple quantum coherence (DQC and ZQC). DQC (I+S+) is selected... 

A complex, multiply bridged 1,2,3,4-adduct of C60 (168) (Scheme 1.11) including a noninherently chiral addition pattern as well as a multitude of stereogenic centers in the addend moiety was obtained in a tandem reaction between the alkaloid scandine and Ceo-324 The sequence included a photoin-duced addition of the tertiary amine subunit of the alkaloid and a [2 + 2] cycloaddition of its vinyl group to the adjacent intrahexagonal formal double bond of the fullerene. The structural elucidation included 1H-1 H COSY-, HMQC- (heteronuclear multiple quantum coherence), HMBC-, and ROESY-(rotating frame Overhauser enhancement spectroscopy) NMR experiments and... 

The structural connectivity derived from examination of the 111, 13C/DEPT, DQF-COSY, HMQC, and HMBC data (DEPT = distortionless enhancement by polarization transfer DQF = double quantum filtering COSY = correlation spectroscopy HMQC = heteronuclear multiple quantum correlation HMBC = heteronuclear multiple bond correlation) resulted in global reevaluation of sclerophytin B structure and demonstrated that this compound and the related alcohol are not composed of two ether bridges as in the originally formulated structure 37, but share the structural features depicted as 38 <20000L1879>. Comparison of 13C and 111 NMR data of Norte s... 

DFT = density functional theory HMQC = heteronuclear multiple quantum coherence SOMO = singly occupied molecular orbital PES = photoelectron spectroscopy Cl = configuration interaction LUMO = lowest unoccupied molecular orbital HOMO = highest occupied molecular orbital TLC = thin layer chromatography. 

HMQC Heteronuclear Multiple Quantum Correlation spectroscopy... 

Chemometric techniques have also been used to identify grapevine cultivars and clones based on the H and NMR of polyphenols observed in extracts/ Extractions from crushed grape seeds and vines obtained in France were analyzed using HMBC and HMQC (heteronuclear multiple quantum correlation) 2D NMR... 

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