S NMR

An extensive static S NMR natural abundance study of 26 sulphides and sulphates has been made by Eckert and Yesinowski (1986). In all these spectra only the central 

116 ppm/K. The trends in the chemical shifts of these sulphides can he explained in terms of electronegativity considerations involving ionicity and bond overlap effects (Eckert and Yesinowski 1986). 

ZnS (wurzite) - 231,-234,-235,-229 0.43 Eckert Yesinowski (1986), Bastow Stuart (1988b), Daunch Rinaldi (1986), Haller et al. (1980) 

NH4A1(S04)2.12Hz0 333,331 0.53 Eckert Yesinowski (1986), Daunch Rinaldi (1996) 

---

The only sulfur isotope with a nuclear spin is which is quadrupolar (/ = 3/2) and of low natural abundance (0.76%). In view of these inherent difficulties and the low symmetry around the sulfur nuclei in most S-N compounds, S NMR spectroscopy has found very limited application in S-N chemistry. However, it is likely that reasonably narrow resonances could be obtained for sulfur in a tetrahedral environment, e.g. [S(N Bu)4], cf. [S04] . On the other hand both selenium and tellurium have isotopes with I = Vi with significant natural abundances ( Se, 7.6% and Te, 7.0%). Consequently, NMR studies using these nuclei can provide useful information for Se-N and Te-N systems. 

Pochapsky, C. and Pochapsky, S., NMR for Physical and Biological Scientists, Garland Science, London, 2006, 350. 

Table 2.3 as a completely worked out example using quantitative solvent extraction, ash content determination, TGA, FTIR, XRF, GC-MS, HS-GC-MS, PyFTIR, ICP, and s-NMR. Information on the cure and antidegradant systems was obtained (assigned species/possible origin), as follows cyclohexane thiol/CBS accelerator benzothiazole/MBT, MBTS or CBS accelerators N, A-dimethylformamide/TMTD accelerator phthalim-ide/Santoguard PVI and IV-phenylbenzene amine/possi-bly a diphenyl/acetone amine antioxidant. 

Highly sophisticated pulse sequences have been developed for the extraction of the desired information from ID and multidimensional NMR spectra [172]. The same techniques can be used for high-resolution 1-NMR, s-NMR and NQR. Pulse experiments are commonly used for the measurement of relaxation times [173], for the study of diffusion processes [174] and for the investigation of chemical reactions [175]. Davies et al. [176] have described naming and proposed reporting of common NMR pulse sequences (IUPAC task group). An overview of pulse sequence experiments has been given [177],... 

Inter-/intramolecular distances 0.1-1 nm Nuclear Overhauser effect (1-NMR), dipolar splittings (s-NMR)... 

In principle, 13C 1-NMR is a more suitable technique than H NMR for identification and characterisation of extracted flame retardants (FRs) as many FRs are partially or totally brominated. However, the solubility of many bromine-containing FRs is often insufficient for 13C NMR experiments in common solvents, such as CDCI3 and tetrachloroethane (TCE), and therefore 13C s-NMR is frequently called in. 

Use of 29Si NMR can generally be avoided in favour of 1II NMR. For example, Narayan et al. [253] have used proton NMR for the detection of a HALS stabiliser based on silicon technology, after extraction from a PP matrix. 170 1-NMR and s-NMR have been used for the study of PP, EPDM, PIP and NR oxidatively degraded with enriched 02 [204,254]. 

As many bromine-containing flame retardants do not dissolve in common NMR solvents (typically CDCI3 and tetrachloroethane), ll 1-NMR can not generally be applied and 13C s-NMR may then be called in. However, in favourable circumstances, e.g. for FR 1025 (poly-pentabromobenzylacrylate, Ameribrom) in PBT (Tribit 1500 GN 30), direct H 1-NMR in C2D2Cl4 of the fraction insoluble in HFIP can be used, in view of the unique resonance position of the benzylacrylate fragment in FR-1025. 

Polymer material/product characterisation crystallinity, amorphous content, phase analysis WAXS, WAXD, SAXS, SALLS, density, DSC, IR, Raman, s-NMR, AFM, optical microscopy, SEM, TEM... 

Product analysis polymer network s-NMR, gelation, swelling, birefringence, IR, NMR, STM, SANS, Brillouin scattering, pulse-propagation... 

Table 1 Chemical shifts S NMR 13C and SCS values for iodofurazans in CDCI3...

Fia. S. NMR lines of a single crystal of a-AljOj with the external magnetic field directed along the c-axis. The frequency is 7.20 mc./second ( 0 = 6490 gauss) and the magnetic field increases from left to right with a total scan of about 2000 gauss. 

---