CPMAS spectroscopy

Cross polarisation from protons to fluorine nuclei becomes feasible with the double-resonance probes developed for F- H work. Figure 6.6.3 shows a CP profile as a function of contact time. This experiment offers similar possibilities for discrimination within spectra that are traditional with C CPMAS spectroscopy. Thus, the dipolar dephasing pulse sequence (Fig. 

Fluorinated charcoal has been studied [141] by F MAS and CPMAS spectroscopy. Dipolar dephasing and variable contact experiments yielded information on asignments and on quantification. Four types of carbon site were recognised, namely graphitic (C), CF, CF CF2 and CF3. 

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... 

Ahmad R, Kookana R, Alston A, Skjestad J (2001) The nature of soil organic matter affects sorption of pesticide. 1. Relationships with carbon chemistry as determined by C-13 CPMAS NMR spectroscopy. Environ Sci Technol... 

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. 

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... 

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. 

Apart from structural factors annular tautomerism is strongly influenced by the aggregate state of the compound. Gas-phase and solid state studies of tautomerism have received much attention recently because of the development of methods such as X-ray crystallography, CPMAS NMR, microwave spectroscopy, etc. Low temperature H NMR is the simplest and most straightforward method to determine Kx it only requires that proton transfer be slow enough to observe separate signals for both tautomers, and that the equilibrium is not shifted too much towards one of the tautomers (about 5% of the minor tautomers seems the limit). More detailed information on tautomerism of key azole systems is given below. 

The concern that the solid state structures do not represent those in the solution phase in which the H NMR data were obtained was addressed by comparing the NMR spectra in both phases. Thus it was demonstrated for 17 and 18 through the use of solid state CPMAS and solution l3C NMR spectroscopy that there were no fundamental differences in the structure or charge distribution of the cation in solution or the solid state91 92. 

The phase transformation behavior of Py-D3C was far simpler than that reported for tetrahydrofuran/N2- and tetrahydrofuran/Xe-D3C in reference 10. We attribute this difference in part to impurities in the samples employed, samples that contained methanol and ethylenediamine according to 13 C CPMAS NMR spectroscopy. We have observed that use of Si(OCH3)4 as a silica source or ethylenediamine as a catalyst in clathrasil synthesis introduces defects that can alter phase transition temperatures by as much as 30 °C and/or introduce new phase transformations. 

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). 

DiCosty, R. J., Weliky, D. P, Anderson, S. J., and Paul, E. A. (2003). 15N-CPMAS nuclear magnetic resonance spectroscopy and biological stability of soil organic nitrogen in whole soil and particle-size fraction. Org. Geochem. 34,1635-1650. 

Kacker, T., Haupt, E. T. K., Garms, C., Francke, W., and Steinhart, H. (2002). Structural characterisation of humic acid-bound PAH residues in soil by BC CPMAS-NMR-spectroscopy evidence of covalent bonds. Chemosphere 48,117-131. 

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