13C chemical shift assignments

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. 

Pig. 3.19. 13C Chemical shift assignments of 1-Methoxycarbonylphenazine (a) in deuteriochloro-form at 30 C based on long-range UC—I5N couplings of the 10-15N-enriched derivative (b). 

X-ray structure (coryphine perchlorate)1 13C Chemical Shift Assignments (CDClj) ... 

Figure 15.6. Example of 13C chemical shift assignments of structural groups found in NOM. The asterisk marks the C atom which is found in the corresponding chemical shift region. Reprinted from Keeler, C., Kelly, E. F., and Maciel, G. E. (2006). Chemical-structural information from solid-state C-13 NMR studies of a suite of humic materials from a lower montane forest soil, Colorado, USA. Geoderma 130,124-140, with permission from Elsevier.

Model compounds based on 2-methyl-2-pentene were studied to supplement the 13C chemical shift assignments of the products from accelerated sulfur vulcanisation of NR. It is observed in the model compound data that it may not be possible to distinguish between a 13C NMR resonance which is due to disulfidic crosslinks and a peak due to pendent accelerator groups, while a large chemical shift difference ( 3 ppm) is observed for the monosulfidic bonds. The MBS-accelerated sample shows similar new resonances as seen in the TMTD accelerated systems. In this comparison however, the quantitative aspects of the data might be obscured due to the differences in the state of cure among the different formulations. 

The appropriate C6D5 deuterated isotopomers of 28, 29 and 32 were also studied. C—D carbons in the deuterated isopotomers behave in dipolar dephased spectra as quaternary carbons and the changes in spectral patterns of nondeuterated and pentadeuterated compounds were used for 13C chemical shift assignment. The spectra of 28, 30, 31 and 32 were also recorded at elevated temperature. It was found, contrary to Maciejewska s results,87 that in 28, 30 and 32 rotation of the aromatic rings is induced at elevated temperatures. 

Recently, structural studies with 13c nuclear magnetic resonance were reportedly for phenoxymethyl and other penicillins and the related sulfoxides. 13c chemical shift assignments were made for the different carbon atoms. 

Recently, the structure of alkaloid A has been revised (102) from 83 to 85, mainly on the basis of 13C NMR spectral correlation of alkaloids A and with those of closely related neoline-type alkaloids. The reinvestigation of the structure of alkaloid A by the, 3C NMR analysis was carried out because the position of acetoxyl group at C-8 in alkaloid A was rendered doubtful by the data from the pyrolysis study. The 13CNMR analysis reveals that an a-acetyl group is present at the C-6 position instead of at C-8 and that a methoxyl group is present at the C-8 position. We have also revised the 13C chemical shift assignments of alkaloid A (85). 

Alkaloid (C22H35NO3 mp 190-19 ) was also isolated in small amounts from D. bicolor (100, 101). It was shown to contain an N-ethyl, a tertiary methyl, a methoxyl, and four hydroxyl groups. Structure 84 was assigned to alkaloid on the basis of comparisons of the 13C chemical shifts for alkaloids A and and their hydrochloride salts with those of deoxylycoctonine and isotalatizidine. Recently, the 13C chemical shift assignments for alkaloid have been revised (102). Because alkaloids A and are closely related and the structure of alkaloid A was revised to 85 with the C-6 a-acetyl group, perhaps the C-6 hydroxyl group in alkaloid is also present in the a-configuration. 

Table 2 summarizes the available 13C chemical shift assignments for monosaccharides and their derivatives. The cited references and... 

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