Chemical shift assignment

Based on NMR chemical shift assignments and the use of recorded spin-spin coupling constants it was determined193 that in both 2,4-diphenyl-substituted thietane oxides (186a,b) the dominant conformers are those in which the S—O bond is equatorial and, therefore, in the trans-2,4-isomer186 one phenyl group (i.e. R1) is syn-axial to the S— O bond, whereas in the cis-2,4-diphenyl isomer 186b both phenyls are anti-equatorial to the S—O bond. 

The GASPE spectrum of podophyllotoxin is shown. The signals at 8 56.0,108.6, and 152.0 each represent two carbons in identical magnetic environments, while the signal at 8 147.6 also represents two carbons that accidentally appear at the same chemical shift. Assign chemical shift values to various protonated and quaternary carbons in the structure. 

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. 

The HETCOR spectrum, C-NMR data, and H-NMR chemical shift assignments of buxoxybenzamine (C35H50N2O5) are presented below. Assign the C-NMR chemical shifts to the various protonated carbons using the HETCOR plot. 

The heteronuclear multiple-quantum coherence (HMQC) spectrum, H-NMR chemical shift assignments, and C-NMR data of podophyllo-toxin are shown. Determine the chemical shifts of various carbons and connected protons. The HMQC spectra provide information about the one-bond correlations of protons and attached carbons. These spectra are fairly straightforward to interpret The correlations are made by noting the position of each crossf)eak and identifying the corresponding 8h and 8c values. Based on this technique, interpret the following spectrum. 

The HMQC spectrum, H-NMR chemical shift assignments, and C-NMR data of vasicinone are shown. Consider the homonuclear correlations obtained from the COSY spectrum in Problem 5.14, and then determine the carbon framework of the spin systems. 

The HMBC spectrum of vasicinone along with the H-NMR assignments are shown. Determine the H/ C long-range heteronuclear shift correlations based on the HMBC experiment, and explain how HMBC correlations are useful in chemical shift assignments of nonprotonated quaternary carbons. 

The NOESY spectrum and H-NMR chemical shift assignments of 7-hydroxyfrullanolide are shown. Interpret the NOESY spectrum. What conclusions can you draw about the stereochemistry at C-6 and C-10 ... 

The HMQC spectrum of podophyllotoxin shows heteronuclear crosspeaks for all 13 protonated carbons. Each cross-peak represents a one-bond correlation between the C nucleus and the attached proton. It also allows us to identify the pairs of geminally coupled protons, since both protons display cross-peaks with the same carbon. For instance, peaks A and B represent the one-bond correlations between protons at 8 4.10 and 4.50 with the carbon at 8 71.0 and thus represent a methylene group (C-15). Cross-peak D is due to the heteronuclear correlation between the C-4 proton at 8 4.70 and the carbon at 8 72.0, assignable to the oxygen-bearing benzylic C-4. Heteronuclear shift correlations between the aromatic protons and carbons are easily distinguishable as cross-peaks J-L, while I represents C/H interactions between the methylenedioxy protons (8 5.90) and the carbon at 8 101.5. The C-NMR and H-NMR chemical shift assignments based on the HMQC cross-peaks are summarized on the structure. 

Table Chemical shift assignments for sy -[(= SiO)Re(= CtBu)(= CHtBu)(CH2tBu)] through the combined use of ID and 2D HETCOR NMR data...

Figure 46.6. Major products identified by C NMR with proposed chemical shift assignments.

Structural properties of both AFA-PLN and WT-PLN bound to SER-CAla after reconstitution in a functional lipid bilayer environment were examined by 13C solid-state NMR.241 Chemical-shift assignments in all domains of AFA-PLN provide direct evidence for the presence of two terminal ot-helices connected by a linker region of reduced structural order that differs from previous findings on free PLN. A combination of the spectroscopic data with biophysical and biochemical data using flexible protein-protein docking simulations provides a structural basis for understanding the interaction between PLN and SERCala.244 Using a... 

Table 1. Structural carbon distribution (%) of the humic acids extracted from soil horizons, adopted from Xing (2001). The distribution was calculated from solid state 13C Cross-Polarization Magic-Angle-Spinning (CP/MAS) NMR spectra. Chemical shift assignment for carbon functional groups alkyl 0-50 ppm O-alkyl 50-117 ppm aromatic 107-165 ppm.

Compounds 1 and 2 were identified by FTIR and 13C-NMR. The 13C proton decoupled spectra for 1 and 2 are dominated by signals ranging from 62 to 195 ppm. The 13C chemical shift assignments were made based on comparisons with 4,4 -(hexafluoroisopropylidene)diphenol and from calculations based on substituted benzenes and naphthalenes.15 The 13C-NMR spectrum clearly showed that the Friedel-Crafts acylation of 1 by 4-fluorobenzoyl chloride yielded the 1,4-addition product exclusively. The 13C chemical shifts for 2 are listed in Table 8.1. The key structural features in the FTIR spectrum of2 include the following absorptions aromatic C-H, 3074 cnr1, ketone C=0, 1658 cm-1, aromatic ether Ar—0—Ar, 1245 cm-1, and C—F, 1175 cm-1. 

N.m.r. spectroscopy T.l.c.-m.s. analysis of oligosaccharides coupled to a lipid amine (neoglycolipids) H n.m.r. spectrum in D20 after exchange of free protons with deuterium Experiments conducted at 295 K, with acetone as the internal standard (set at 2.225 p.p.m. from 4,4-dimethyl-4-silapentane-1-sulfonate) Results compared, to within 0.005 p.p.m. (laboratory-to-la-boratory variation) of data in the literature Conformational studies by n.O.e. experiments Natural-abundance-13C analysis Chemical-shift assignment by 2D H- H and H-13C n.m.r. spectroscopy... 

Pseudopterosin X (1) was isolated as a yellow colored gum. The UV spectrum of 1 showed maximum absorption at 280 nm due to the presence of a highly substituted benzene chromophore [10], Its IR spectmm displayed intense absorption bands at 3,470 (OH), 2,904 (CH), 1,705 (C = O), 1,595 (C = C) and 1,100 (C-0) cm . The high-resolution electron-impact mass spectmm (HREIMS) of 1 showed M+ at m/z 474.2622, and this mass provided molecular formula indicating the presence of nine double bond equivalents in 1. The C-NMR chemical shift assignments of 1 are shown around stracture 1. On the basis of the detailed NMR studies and comparison with the reported pseudopterosins in the literature and L-xylose [3-5], stmcture 1 was proposed for this new natural product. 

The C NMR spectmm of 13 showed the resonances of all 35 carbon atoms. A combirration of broadband C-NMR and DEPT spectra indicated the presence of 7 methyl, 4 methylene, 16 methine and 8 quaterrrary carbon atoms in compound 13. Complete 13C-NMR chemical shift assignments of 13 are shown around structure 13. Based on these spectral data, structure 13 was established for this new compound. 

In order to prepare NiPz (4) derivative, H Pz was reacted with Ni(Ac)j.4HjO in the mixture of chloroform and ethanol to obtain NrPz. In the H- NMR spectram of NiPz, chemical shifts assignable to -SCH, C-CH -C, -CH and -CH groups at 4.2,... 

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