Heteronuclear Multiple-Bond Correlation HMBC

In the case of the 7-hydroxy-substituted compounds 44 (Scheme 2), 54 different derivatives were investigated by 13C NMR spectroscopy and, in some cases, also by 1SN NMR spectroscopy <1995JST(335)273>. With the help of proton-coupled 13C NMR spectra, semi-selective INEPT (insensitive nuclei enhanced by polarization transfer) experiments, and heteronuclear multiple bond correlation (HMBC) two-dimensional 2D-NMR spectra, all shifts could be unequivocally assigned. While the C-7 shifts did not allow the existing tautomeric situation to be determined, a clear decision could be made by H NMR spectroscopy in this respect. The 1SN NMR spectra revealed an equilibrium between the N(4)H and N(3)H tautomeric forms, which is fast on the NMR timescale. 

Heteronuclear multiple bond correlation (HMBC) [1, 2] is one of the most powerful NMR techniques and is now being widely used for structural analysis of complicated molecules. Since it detects long range... 

There are a number of techniques stemming from the basic two-dimensional technique, which for example allow correlation between carbon atoms and the protons attached to them and correlations of carbon atoms with protons one or two bonds removed from them, heteronuclear multiple bond correlation (HMBC). 

NMR experiments. Heteronuclear NMR experiments are represented by H C HSQC (Figure 2.1) and heteronuclear multiple bond correlation HMBC) (Figure 2.2)... 

Product elucidation of trimethyloxonium tetrafluoroborate and methyl iodide reactions with [l,2,3]triazolo[4,5- -pyridazines (Schemes 1-3) using mainly 2-D heteronuclear multiple bond correlation (HMBC). NMR... 

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. 

Complete N NMR chemical shifts together with H- N coupling constants (referenced externally to NH4C1 in DMSO-1 6 DMSO - dimethyl sulfoxide) have been determined for toxoflavin 7 and fervenulin 8 in CDCI3 using pulsed field gradient heteronuclear multiple bond correlation (HMBC) techniques <2000H(52)811>, and are presented in Table 1. 

Inverse-detected experiments have had the greatest effect in making 15N NMR experiments feasible for small samples. These experiments take advantage of the higher sensitivity of NMR to facilitate the observation of insensitive nuclei like 13C and 15N. The H-13C heteronuclear multiple quantum coherence (HMQC) and the related heteronuclear multiple-bond correlation (HMBC) experiments are important in contemporary natural products... 

Record the 2-D H-13C heteronuclear multiple bond correlation (HMBC) spectrum (Braun et al., 1998, pp. 489-492). 

The heteronuclear multiple bond correlation (HMBC) experiment correlates proton nuclei with carbon nuclei that are separated by more than one bond. In Fig. FI. 4.7 the 37CH and 27Ch couplings dominate. Major applications related to anthocyanins include the assignment of resonances of nonprotonated carbon nuclei of the... 

Notably, two isomeric products can be generated. The usual infrared (IR) and mass spectra as well as H and 13C NMR chemical shifts could not define which isomer was formed. The authors used different NMR techniques, such as 2-D heteronuclear multiple bond correlation (HMBC) experiments and phase-sensitive nuclear overhauser enhancement spectroscopy (NOESY) measurements to elucidate the product s structure. 

Heteronuclear multiple bond correlation HMBC - C 2-4 bond correlations. Quaternary carbon are observed... 

Snider and Duvall published the first geminal coupling constant in the case of the 1,2-oxazetidine carboxylate derivative 28a (Table 1 Figure 9) and confirmed the formation of the four-membered ring by means of heteronuclear multiple bond correlations (HMBC) (Table 1) <2003TL3067>. Vicinal coupling constant values 37h-h are now available in the... 

UNDERSTANDING THE HETERONUCLEAR MULTIPLE-BOND CORRELATION (HMBC) PULSE SEQUENCE... 

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