13C CPMAS NMR spectroscopy

In the list of diazoketones studied by us95 mostly derivatives were included which have in solution no or only a small tendency for a Wolff rearrangement. Nevertheless we found not a single diazoketone 71 which enabled us to identify a ketocarbene 72, only the corresponding ketenes 73 could be detected. The same observation was made when we studied in collaboration with Yannoni et al." the photochemically induced deazotation of l-diazo-2-propanone in an organic matrix at 77 K, using 13C CPMAS NMR spectroscopy as the analytical tool. 

The structures of 4-aryl-2,3-dihydro-lH-pyrido[l,2-c]pyrimidine-l,3-diones hydrochlorides 50 were characterized by solid-state 13C CPMAS NMR spectroscopy (08JST325). 

The two isocyanate groups of BICDPM react with amino groups of the PVFA-co-PVAm chains as well as with silanol groups of the silica surface. Structure analysis of PVFA-co-PVAm/silica particles cross-linked with BICDPM was carried out by means of solid state 13C CPMAS NMR spectroscopy (Fig. 6) and XPS (Fig. 2b). 

The study of HS extracted from both fractions (pellets and matrices) was performed by various geochemical analyses CHONS elemental analysis, Fourier-transformed infrared spectroscopy (FTIR) and solid-state 13C CPMAS NMR. 

C CPMAS NMR studies of NH-pyrazoles and indazoles <1993CJC678> concluded that (1) the tautomer present in the solid is also the major tautomer in solution (2) certain pyrazole C-substituents (CF3, Br, Ar, Het) prefer position 3 (i.e., they are 3-substituted pyrazoles 239) whereas others (Bu1, Pr1, CH3) prefer position 5 (i.e., they are 5-substituted pyrazoles 240) (3) 3(5)-ferrocenylpyrazole should be a 50 50 mixture of both tautomers in the solid state. Low-temperature 13C NMR spectroscopy of 3(5)-phenylpyrazole shows that at -20 °C it exists as a mixture of 80% of the 3-phenyl tautomer 239 (R1 = H, R2 = Ph) and 20% of the 5-phenyl tautomer 240 (R1 = H, R2 = Ph) <1991G477>. 

Sometimes decomposition reactions can be avoided by carrying out diazotizations in concentrated sulfuric acid. By this method Law et al. (1991) obtained the 1,5-bisdiazonium salt (incorrectly called tetrazonium salt) of l,5-diamino-4,8-dihy-droxy-anthraquinone, which is deprotonated to 2.28. The structure was verified by cross-polarization magic angle spinning (CPMAS) 13C NMR spectroscopy. 

NMR spectroscopy (31P, II, 13C) and mass spectrometery have been extensively employed for establishing structures of the diazaphospholes. The solid state 13C and 15N CPMAS NMR spectra of 3,5-di-substituted [l,2,4]diazaphospholes have been recorded [78]. Several X-ray crystal structures have been reported for a number of... 

Carbocations have been generated in zeolites and were characterized by CPMAS 13C NMR spectroscopy and accompanying quantum chemical calculations.110 13C NMR isotropic shifts calculated at the GIAO-MP2/TZP/DZ level for the 1, 3-dimethylcyclopentenyl (98) and 1,2,3-trimethylcyclopentenyl cations (99)111 are in agreement with the observed experimental spectra of the carbocations in the zeolite.112... 

After a paper devoted to GIAO/B3LYP calculations of 13 monosubstituted benzenes and 21 1-substituted pyrazoles [148] that allowed discussion of some structural problems (such as conformation, tautomerism, and structure of salts) we have continued to use this combination of experimental (in solution and in the solid state, CPMAS NMR) and calculated values as a very useful exploratory technique. For instance, we have used II, 13C, and 15NNMR spectroscopy to study compounds 149-154. In para-disubstituted derivatives 149,151,152,153, in the solid state (no free rotation) the signals of the ortho carbons are split (one is close to N2) and, thanks to the calculated values, they can be assigned [149],... 

Rethwisch DG, Jacintha MA, Dybowski CR. 1993. Quantitation of 13C in solids using CPMAS-DD-NMR spectroscopy. Anal. Chim. Acta 283 1033-1043. 

Beyer, L., Schulten, H.-R., Freund, R., and Irmler, U., Formation and properties of organic matter in a forest soil, as revealed by its biological activity, wet chemical analysis, CPMAS 13C-NMR spectroscopy and pyrolysis field ionization MS, Soil Biol. Biochem., 25, 587-596, 1993. 

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