NMR SPECTRAL ANALYSIS

Determined on crude reaction mixture by H-NMR spectroscopy (400 MHz). d 90-95% from H-NMR spectral analysis. 

Nuzillard, J-M. and Emerenciano, V.D.P., Automatic structure elucidation through data base search and 2D NMR spectral analysis, Nat. Prod. Comms. 1, 57, 2006. 

Corsaro and co-workers studied the reaction of pyridazine, pyrimidine, and pyrazine with benzonitrile oxide and utilized H NMR spectral analysis to determine the exact structure of all the cyclized products obtained from these reactions <1996T6421>, the results of which are outlined in Table 1. The structure of the bis-adduct product 21 of reaction of pyridazine with benzonitrile oxide was determined from the chemical shifts of the 4- and 5-isoxazolinic protons at 3.76 and 4.78 ppm and coupled with the azomethine H at 6.85 ppm and with the 5-oxadiazolinic H at 5.07 ppm, respectively. They determined that the bis-adduct possessed /(-stereochemistry as a result of the large vicinal coupling constant (9.1 Hz). Similarly, the relative stereochemistry of the bis-adducts of the pyrimidine products 22-25 and pyrazine products 26, 27 was determined from the vicinal coupling constants. 

Yamagishi and coworkers44 reported a structure determination of rumbrin 74, a new cytoprotective substance. Its structure was elucidated by NMR spectral analysis and was found to possess a novel skeleton containing a-pyrone, tetraene and pyrrole moieties. 

The structure was determined by NMR spectral analysis including a variety of two-dimensional NMR techniques. The 500-MHz XH NMR spectrum of 77 taken in CDCI3 (Figure 26) revealed the presence of 5 aromatic protons, 15 olefinic protons, a methoxy (63.65), an allylic methyl (62.14) and a tertiary methyl group (61.33). The 13C NMR spectrum showed signals due to all 34 carbons, which were assigned to 7 quaternary carbons, 23 methines, 1 methylene and 3 methyls by DEPT experiments. The 13C and XH NMR spectral data are summarized in Table 27. 

Figure 10 shows a spectrum of butyl rubber gum stock obtained on the solid at 80°C using normal pulsed FT techniques. Clearly it could be identified as a component in fabricated materials by direct nmr spectral analysis. Figure 11 shows spectra obtained from various portions of typical rubber products. These samples were cut from the rubber product, placed in an nmr tube without solvent, and spectra obtained at an elevated temperature. The data show how polyisoprene, a polyisoprene/polybutadiene blend and a polyisobutylene/polyisoprene/polybutadiene rubber blend are quickly identified in the materials. Figure 11a shows processing oil was present, and which was confirmed by solvent extraction. 

Drosopterin (87a) and isodrosopterin (87b) have been prepared by treatment of 7,8-dihydropterin (593) with p-hydroxy-a-ketobutyric acid (595) or a-hy-droxyacetoacetic acid (601) (506). Their initially proposed structures (507) have been revised to 87 (see Scheme 76) on the basis of detailed, H-NMR spectral analysis of 6,7-dimethyldrosopterin (602), which was prepared by treatment of 7-methyl-7,8-dihydropterin (603) with a-hydroxyacetoacetic acid (601) (50S). Structures of other drosopterins (88-90) have not yet been established. 

For D-HMBC experiments, we usually omit the low pass J-filter (the first 90° pulse for C nucleus in the HMBC pulse sequence) aiming to suppress the cross peaks due to the direct Jc-h correlation, but it can be implemented if desirable. In the D-HMBC spectra, the cross peaks between directly bonded C and H do not, in most cases, hinder the easy analysis of the spectra, because these cross peaks appear as singlets. On the contrary, these peaks even contribute to easy NMR spectral analysis when HMQC spectral data are not in hand. 

Terahara, N. and Yamaguchi, M., IH NMR spectral analysis of the malylated anthocyanins from Dianthus, Phytochemistry, 25, 2906, 1986. 

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