Heteronuclear multiple-quantum correlation

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 ... 

A variety of examples of 2D-NMR experiments is provided in reference [21]. The structure elucidation of the di-rhodium compound shown in Figure 11.3 was mostly carried out in this way. For example, 2D 11 l-31P heteronuclear multiple quantum correlation (HMQC) experiments were used to show that two rhodium-coupled hydride resonances are connected to a single type of 31P nucleus. 

The first of the proton-detected experiments is the Heteronuclear Multiple Quantum Correlation HMQC experiment of Bax, Griffey and Hawkins reported in 1983, which was first demonstrated using 1H-15N heteronuclear shift correlation [42]. The version that has come into wide-spread usage, particularly among the natural products community, is that of Bax and Subramanian reported in 1986 [43]. A more contemporary gradient-enhanced version of the experiment is shown in Fig. 10.14 [44],... 

Nuclear Overhauser effect (NOE) difference measurements were used to assign structure 79 for the product of reaction of diphenylnitrile imine with 5-ethylsulfonyl-2-methyl(27/)pyridazinone. Thus in the H NMR spectrum the ot/, o-protons of the arylhydrazino moiety (which were identified by two-dimensional heteronuclear multiple quantum correlation (2-D HMQC) spectroscopy) were shown in differential NOE (DNOE) experiment to be significantly enhanced on irradiation of pyridazine hydrogen H-7, proving their steric proximity <2000JST13>. 

The structural assignment of both 29 and 30 was accomplished through extensive two-dimensional (2-D) NMR heteronuclear multiple quantum correlation (HMQC) and heteronuclear multiple bond correlation (HMBC) spectroscopic studies <2004T8189>. In the HMBC spectrum of 29, the proton at 8.64p.p.m. shows a strong correlation Jq-h with the carbonyl carbon (C-10) at 180.9 ppm and the proton at 8.82p.p.m. with the carbonyl carbon (C-5) at 181.7 ppm. The HMBC spectrum of 30 shows a significant strong correlation Vq h of the C-5 carbonyl carbon with the H-6 proton at 8.52 ppm and the H-4 proton at 8.52p.p.m. 

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... 

Hydroxyethyl methacrylate Human immunodeficiency virus 1,1,1,3,3,3,-Hexamethyldisilazane Hydrophobically modified polycationic dextran Heteronuclear multiple quantum correlation High performance liquid chromatography Herpes simplex virus... 

The vast literature associated with flavanoid chemistry precludes a discussion here but two valuable reviews have been published. The first reviews a number of spectroscopic techniques used for flavonoid analysis, with a strong emphasis on NMR spectroscopy (plus also mass spectrometry, vibrational spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, X-ray crystallography, and circular dichrosim (CD)) . The second review deals with NMR methods that have been successful in the characterization of phenolic acids and flavonoids from plant extracts that have not been separated or isolated as single components. The emphasis of the article is 2-D NMR methodology and a variety of experiments such as total correlated spectroscopy (TOCSY), COSY, nuclear Overhauser enhancement spectroscopy (NOESY) and heteronuclear multiple quantum correlation (HMQC) are discussed . 

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... 

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... 

Similar to the HSQC experiment, multiple quantum coherences can be used to correlate protons with Q-coupled heteronuclei. The information content of the Heteronuclear Multiple Quantum Correlation (HMQC) experiment (56) is equivalent to the HSQC, but the sensitivity can be improved in certain cases. Additionally, by proper tuning of delays and phase cycling, it can be transformed into the heteronuclear multiple bond correlation experiment (57-59), which results in correlations between J- and J-coupled nuclei. 

---