Resonance assignment chemical shifts

Llsinoprll, Proton Magnetic Resonance Assignments Chemical Shift. 8H (ppm) Assignment ... 

The H and nuclear magnetic resonance (NMR) chemical shift of all the parent structures are fully reported in CHEC-II(1996) <1996CHEC-II(6)447>. Since then, the complete proton and carbon chemical shift assignments have been made for 2- and 3-formyl, acetyl, or methyl phenoxathiin <1996PJC36>. 

The carbons of interest in DHA are C4, C5, and C6. Carbons-1, -2, and -3 appear as singlets. Carbons-4 and -5 appear as doublets, and C6 appears as a triplet. Because C4 and C5 both appear as doublets, assigning chemical shifts to these carbons without further information would be diflBcult. It was important, therefore, to perform a series of single-frequency proton-carbon decoupling experiments, while maintaining the oflF-resonance decoupling. 

Carbon atom Resonance Triad assignment Chemical shift (ppm)... 

Fig. 5. Proton magnetic resonance spectra (100 MHz) for batrachotoxin class alkaloids and assignments. Chemical shifts in ppm (5) for deuterochloroform with a tetramethylsilane standard. Assignments A pyrrole NH B pyrrole 5-H C olefinic proton at C-7 D oleflnic proton at C-16 proton at C-20 FI4-OCH2 and proton at C-11 G one proton at C-15, the other appears at 6 2.3 methylene protons at C-18 / pyrrole 2-CH3 T and / pyrrole 2-CH2CH3 / NCH3 K pyrrole 4-CH3 L 2I-CH3 M I9-CH3 (see Fig. 4)...

Fig. 10. Structure of perhydrohistrionicotoxin (dodecahydro) and proton magnetic resonance spectral assignments. Chemical shifts are ppm for deuterochloroform (253). The proton magnetic resonance spectrum (100 MHz) of perhydrohistrionicotoxin is depicted in Tokuyama etal. (253). See Table 8 for chemical shifts of Ha, Hb and He in various naturally...

The C line assignments were made from the combination of DEPT and 2D C- H correlated spectroscopy despite the complexity of the conventional C spectrum. DEPT spectroscopy allowed the multiplicity of each resonance to be determined unambiguously. Hence, C assignments were made easily from the 2D C- H correlated spectrum even in situations where overlap of methine and methylene signals occurs in the proton spectrum. Furthermore, equivalent and nonequivalent methylenes were distinguished in the 2D C- H correlated spectrum, and this allowed assignments to be made despite spectral overlap of proton resonances. Proton chemical shifts were determined more accurately from the correlated... 

After the introduction of C-labels into the protein or glycoprotein molecule, the ability to assign the resonances to specific carbon atoms is essential. In the case of glycophorin (see Fig. 1), it may readily be seen that 5 lysine residues and 1 N-terminal amino acid (per species) can be reduc-tively di[ C]methylated. This could theoretically lead to 6 resonances (or possibly more, if chemical-shift nonequivalence is observed for the dimethyl species) in the C spectrum of methylated glycophorin A. However, in most cases, the N, N -di[ C]methyllysine resonances all occur near, or at, the same frequency. It is then necessary to be able at least to assign, or... 

The broad-band decoupled C-NMR spectrum of ethyl acrylate shows five carbon resonances the DEPT (6 = 135°) spectrum displays only four signals i.e., only the protonated carbons appear, since the quaternary carbonyl carbon signal does not appear in the DEPT spectrum. The CH and CH3 carbons appear with positive amplitudes, and the CHj carbons appear with negative amplitudes. The DEPT (6 = 90°) spectrum displays only the methine carbons. It is therefore possible to distinguish between CH3 carbons from CH carbons. Since the broadband decoupled C spectrum contains all carbons (including quaternary carbons), whereas the DEPT spectra do not show the quaternary carbons, it is possible to differentiate between quaternary carbons from CH, CHj, and CH3 carbons by examining the additional peaks in the broad-band spectrum versus DEPT spectra. The chemical shifts assigned to the various carbons are presented around the structure. 

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