CP MAS spectra

Fig. 6. The CP/MAS spectra of cellulose acetate-butyrate (CAB) and of cellulose acetate (CA, degree of substitution = 1.97), 20. The observation frequency was 50.1 MHz and the irradiation frequency 199.5 MHz. The pulse repetition time was 5 s and the contact time 2 ms. For CAB 400 scans and for CA 60 scans were collected...

The problems involved in the study of humic substances are, as expected, also encountered in the case of fossil fuels. Most C-13 CP/MAS spectra of solid fossil fuels (coals, oil shales) do not exhibit a high level of spectral resolution50,51). They consist essentially of two broad bands — one in the aromatic/olefinic region from about 170 ppm to 95 ppm and one in the aliphatic region from about 90 to —5 ppm relative to TMS. On the other hand, lignite, an imperfectly formed coal, shows a considerable amount of fine structure. 

Fig. 49 Phosphorus-31 CP/MAS spectra of polycrystalline triphenylphosphine (powder) at the given spinning rates...

Dynamic motion of the alkyl stationary phases can also be obtained from NMR studies through an analysis of line shapes, comparisons between single-pulse (SP) and CP-MAS spectra, and various relaxation time constants. Zeigler and Maciel... 

Fig. 19 CP-MAS spectra of samples after treatment at 200 °C for 6h in air a VBS molecule, b ZnsAl/VBS and c Zn2Al/VBS...

Fig.20 C CP-MAS spectra of a Ca2Al/VBS, and b Zn2Al/VBS after heat treatment at different temperatures in air. (Reprinted from [70] with permission from Elsevier)...

Figure 7.7 displays C CP MAS spectra of 1 and 6 recorded at the spinning rate of 10kHz at ambient temperature. Two well-defined NMR signals at 29.0 and... 

Figure 7.7 75.46MHz C NMR solid state CP MAS spectra of compounds 1 (a) and 6 (b) at spinning speed lOkHz.

Finally, an interesting temperature effect was observed in the spectra of a-(phenylthio)benzyUithium 3THF (3, Scheme l) . Differences exist in the C and Li CP/MAS spectra observed at 293 and 208 K, respectively, which indicate a phase transition. This was confirmed by differential scanning calorimetry (DSC), which yielded a transition temperature of 204-212 K. The most characteristic NMR parameters of the... 

Figure 2. 13C NMR solid state difference spectra of (a) L. leucocephala and (b) T. aestivum (24) root tissue previously administered [1-13C] ferulic acid 5a. Fig. 2c shows the difference spectrum of a DHP polymer, derived from [1-13C] coniferyl alcohol 2a (29). CP/MAS spectra were obtained at 50 MHz on a Varian XL-200 Spectrophotometer equipped with a Doty Scientific MAS Probe. SSB = spinning side band.

Fig. 7 CP-MAS spectra of squaric acid, peak assignment and temperature variation in the close vicinity of its paraelectric-antiferroelectric phase transition [24], Note the pronounced coexistence of the spectra from the two phases...

Fig. 12. 75.4-MHz 13C CP/MAS spectra showing the formation of cyclopentenyl cations 8 from cycIopentene-13Ci (random) on zeolite HZSM-5 and 4 from propene-2-,3C on zeolite UY.

Fig. 13. 90.5-MHz 13C CP/MAS spectra of allyl-/-l3C alcohol (spectra a and b) and propanal-I-13C (spectra c and d) on zeolite FIZSM-5. All the spectra were acquired at ambient temperature (a) after heating for 5 h at 323 K (b) after heating at 393 K for 0.5 h (c) prior to heating (d) after heating at 353 K for 0.5 h. The downfield spectral features in spectra c and d, e.g., the isotropic shifts and the number of resonances, are consistent with those derived from allyl-/-l3C alcohol on HZSM-5 (spectra a and b), thus providing unambiguous evidence that the disputed resonance at 216 ppm is propanal-7-l3C. See Xu et at. (Ill) for a more detailed assignment of the resonances.

Fig. 28. 36-MHz l5N CP/MAS spectra of pyridine-15N on zeolite HY. The experimental conditions were all the same for (a) and (b), except that sample b was extensively dealuminated by increasing the activation temperature to SSITC (400°C for sample a). Both spectra were acquired at 77 K to prevent chemical exchanges on the NMR time scale, (a) The single resonance at —176 ppm as well as its associated sidebands indicates protonation of pyridine by the Brpnsted sites, (b) In addition to the protonated pyridine, four additional resonances at -68, -88, —116, and -140 ppm are also seen, indicating complexation of pyridine with different extraframework Lewis sites.

The l3C CP MAS spectra of the sample-A show the presence of the most prominent peak at 27.2 ppm for Ci carbon atom adjacent to the SH group and C2 carbon atom of the 3-mercaptopropyl group. There was another minor intensity broad peak at around 22.3 ppm which is assigned to C and C2 carbon atoms of the dipropyl disulfide. The presence of dipropyl disulfide in the sample A may be due to oxidative dehydrogenation of two adjacent thiol groups leading to the formation of disulfide (S-S) group. An unresolved shoulder down field to the C3 carbon of the thiol was observed for the C3 carbon of the dipropyl disulfide. Similar results were obtained by Lim et al. [6],... 

An example for the polymer network characterization by the 13C CP MAS NMR is shown in Fig. 35. The chemical structure of the cured polystyrylpyridine resins (PSP), synthesized from terephthalic aldehyde and collidine (2,4,6-trimethylpyridine), is determined from CP-MAS spectra by comparison with the solution state spectra of the model compounds and supported by selective DD observations. The CH and CH2 of the crosslinking points, as deduced from the model BP2, give rise to a composite line at about 45 ppm the assignment of other signals is indicated in the figure 239). 

Figure 2. CP/MAS spectra of PSOC-2 and PSOC-858 whole coals and the maceral groups separated from the coal by density gradient centrifugation. The density ranges represent the range of densities employed as indicated in Figure 1. The corresponding fa values are given for each sample.

---