Solid State 6 13C NMR

This is where solid state NMR starts to come into its own. Molecules which form crystals can be studied routinely by X-ray crystallography, which gives exact structural information. This information is limited in value, however, 

Thus solid state NMR can be considered as a (potential) bridge between solution NMR and X-ray crystallography. 

The use of magic-angle spinning (MAS) and cross-polarization (CP) techniques has enabled high-resolution 13C NMR spectra to be obtained in the solid state. Yannoni, Myhre, and Fyfe have obtained solid-state NMR spectra of frozen carbocation 

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Characterization439 Inherent viscosity before and after solid-sate polymerization is 0.46 and 3.20 dL/g, respectively (0.5 g/dL in pentafluorophenol at 25°C). DSC Tg = 135°C, Tm = 317°C. A copolyester of similar composition440 exhibited a liquid crystalline behavior with crystal-nematic and nematic-isotropic transition temperatures at 307 and 410°C, respectively (measured by DSC and hot-stage polarizing microscopy). The high-resolution solid-state 13C NMR study of a copolyester with a composition corresponding to z2/zi = 1-35 has been reported.441... 

Experimental NRM. Solid-state 13C NMR spectra were collected on a homebuilt spectrometer which operates at a proton resonance frequency of 127.00 MHz, corresponding to a carbon resonance frequency of 31.94 MHz, and employs a... 

Zinc complex formation with 1,3-diketones in aqueous solution has been investigated with pentane-2,4-dione, l,l,l-trifluoropentane-2,4-dione, and 4,4,4-trifluoro-l-(2-thienyl)butane-l, 3-dione. The buffer dimethylarsinic acid was shown to have a catalytic effect on complex formation with pentane-2,4-dione and the proton transfer reactions were affected.471,472 High-resolution solid state 13C NMR studies of bis(2,4-pentanedionato) zinc complexes have been carried out.473... 

A pyridine derivative related to dien with respect to the number and distribution of N-donor atoms, namely bis(2-pyridylmethyl)amine (bpma), also gives comparable complexes with Cd, e.g., [Cd(bpma)2](C104)2 with potentially three isomers (including a pair of enantiomers). As shown by the structure analysis (C2/c, Z = 4), a distorted octahedral fac-isomer with symmetry 2 —C2 has been isolated, necessarily with both enantiomers in the crystal lattice. No significant difference in the two kinds of Cd—N bonds (rav(Cd—N) 235.0 pm) is observed.189 Solid-state 13C NMR spectra of this complex and related Mn and Zn complexes have been discussed. 

In a combined elemental microanalysis (to determine the C, H, N and Cl contents of char), TGA, DSC, mid-infrared and NMR study of the char forming process in polychloroprene, CPMAS solid-state 13C NMR was used to probe for structural changes that occurred during the degradation steps [88]. The NMR study supplied both valuable extra detail and confirmatory and complementary information. It was observed that while the dehydrochlorination of polychlo-prene proceeded, there was loss of sp3-hybridised carbon and commensurate... 

The solid state 13C NMR signals of OE in its complexes with a-CD appeared separately from the spectra of a-CD-PEG complexes in a higher magnetic field, in which the signals of the two components were overlapped. This... 

Malcolm RE, Vaughan D (1979) Effects of humic acid fraction on invertase activities in plant tissues. Soil Biol Biochem 11 65-72 Malcolm RL (1989) Application of solid-state 13C NMR spectroscopy to geochemical studies of humic substances. In Hayes MHB, MacCarthy P, Malcolm RL, Swift RS (eds) Humic substances II. In search of structure. Wiley, Chichester, UK, pp 339-372... 

Solid state 13C NMR spectroscopy has emerged as a very useful tool for characterizing SOM (Kinchesh et al. 1995 Preston 1996). Several workers have reported that Koc of HOCs was linearly or exponentially related to the aromatic carbon contents of HAs or whole soils as determined by 13C NMR analysis (Ahmad et al. 2001 Chen et al. 1996 Chin et al. 1997 Gauthier et al. 1987 Perminova et al. 1999). The Koc value of humic materials can vary by as much as an order of magnitude, depending upon their origins (Fig. 1). 

The use of solid state 13C NMR spectroscopy along with elemental analysis provides useful information on the chemical composition of SOM samples. In assessing the influence of SOM composition on the partition of... 

Kolbl A, Kogel-Knabner I (2004) Content and composition of free and occuluded particulate organic matter in a differently textured arable Cambisol as revealed by solid-state 13C NMR spectroscopy. J Plant Nutr Soil Sci 167 45-53... 

As mentioned before, fosinopril sodium is known to be capable of existing in two polymorphic forms, and the diffuse reflectance IR spectra of the two forms indicated that the two structures differed in the conformation of one sidechain. The solid state 13C NMR spectra obtained on both forms were found to confirm this hypothesis [19]. As may be seen in Fig. 3, the significant spectral differences were all associated with nuclei contained within the acetal sidechain. 

Fig. 3 Solid state 13C NMR spectra obtained on the A-phase and B-phase polymorphs of fosinopril sodium, illustrating the differences observed in the CH aliphatic and CC aliphatic regions of the spectrum. (Data adapted from Ref. 19.)...

In the case of DuP747 [24], XRD, DSC, and thermomicroscopic studies determined the polymorphic system to be monotropic. Distinct diffuse reflectance IR, Raman, and solid state 13C NMR spectra existed for each physical form. The complementary nature of IR and Raman gave evidence that the polymorphic pair were roughly equivalent in conformation. It was concluded that the polymorphic character of DuP 747 resulted from different modes of packing. Further crystallographic information is required in order to determine the crystal packing and molecular confirmation of this polymorphic system. 

Analogous to the DuP 747 study, complete crystallographic information was not possible on the fosinopril sodium polymorphic system [25], Two known polymorphs (A and B) were studied via a multidisciplinary approach (XRD, IR, NMR, and thermal analysis). Complementary spectral data from IR and solid state 13C NMR revealed that the environment of the acetal sidechain of fosinopril sodium differed in the two forms. In addition, possible cis-trans isomerization about the CgN peptide bond may exist. These conformational differences are postulated as the origin of the observed polymorphism in fosinopril sodium in the absence of the crystallographic data for form B (single crystals not available). 

Finally, a series of papers have been published on the solid state NMR spectra of a number of analgesic drugs. Jagannathan recorded the solid state 13C NMR spectrum of acetaminophen in bulk and dosage forms [60], From the solution-phase NMR spectrum, assignments of the solid state NMR resonances could be made in addition to explanations for the doublet structure of some resonances (dipolar coupling). Spectra of the dosage product from two sources indicated... 

In the present work, we use quantitative solid-state 13C NMR spectroscopy to study the polymerization process of multiacrylates and the effects of thermal history/aging on the free radical life in polymultiacrylates. 

For NMR spectroscopic experiments, a thin film of pTrMPTrA was prepared by reacting a quantity of monomer and photoinitiator confined between glass plates with 1 mm separation. The polymerization conditions were the same as those for the photocalorimetry experiments. After 1 hour of UV exposure, the film was removed from the plates and ground to a fine powder using a mortar and pestle. A solid-state 13C NMR spectrum of the powder was obtained immediately, as described below. The remaining polymer powder was divided into two portions, one of which was stored under atmospheric conditions. The other portion was stored under N2. After one week, 13c spectra were again obtained for each of these polymer samples. Both samples were then heated to 280 °C in a vacuum oven and analyzed once more by 13C NMR spectroscopy. 

Solid-state 13C NMR spectra were obtained on a General Electric Omega PSG 400 spectrometer operating at 100.6 MHz for l3C nuclei using a Doty Scientific 5 mm high speed MAS probe. The various NMR experiments performed in this study are shown schematically in Figure 1. The carbon chemical shift scale (11) and 90 degree... 

Figure 2.25 Solid-state 13C NMR CPMAS spectrum of form III of iP4MP.152...

The X-ray diffraction patterns and the corresponding solid-state 13C NMR spectra of samples of sPP crystallized in forms I and II are reported in Figure 2.45. Samples of sPP which present X-ray powder diffraction pattern typical of the stable form I (Figure 2.45a) show the usual solid-state 13C NMR... 

CPMAS spectrum typical of the regular twofold helical conformation (Figure 2.45b).147 191 Samples of sPP which present X-ray powder diffraction patterns typical of the isochiral form II (Figure 2.45c) show a different solid-state 13C NMR spectrum with additional signals in the region of the methylene and methyl carbon resonances (Figure 2A5d). These additional resonances have... 

Figure 2.45 X-ray powder diffraction patterns of sPP samples in (a) form I and (b) form II and (c,d) corresponding solid-state 13C NMR CPMAS spectra.

Lorenz, K., Preston, C.M., Kandeler, E. 2006. Soil organic matter in urban soils Estimation of elemental carbon by thermal oxidation and characterization of organic matter by solid-state 13C NMR spectroscopy. Geoderma, 130, 312-323. 

Figure 18.16. Solid State 13C-NMR spectrum of PNT-N prepared by solution polymerization in benzene.

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