High Resolution 13C NMR

The application of 13C NMR for the rapid analysis of the oil composition of oil seeds is well known [16], 13C NMR has recently been applied to the quantitative analysis of the most abundant fatty acids in olive oil [17]. The values obtained by this method differed by only up to 5% compared with GLC analysis. The quantitative analysis was applied to the olefmic region of the high resolution 13C NMR spectrum of virgin olive oil to detect adulteration by other oils which differed significantly in their fatty acid composition. The application of the methodology for the detection of adulteration of olive oil by hazelnut oil is more challenging as both oils have similar chemical profiles and further experiments are in progress. 

We have chosen the PVC diad and triad compounds 2,4-dichloropentane (DCP) and 2,4,6-trichloroheptane(TCH) as subjects for our attempt to obtain quantitative kinetic data characterizing their (n-Bu)3SnH reduction in the hope that they will serve as useful models tor the reduction of PVC to E-V copolymers. Unlike the polymers (PVC and E-V), DCP and TCH are low molecular weight liquids whose high resolution 13C NMR spectra can be recorded from their concentrated solutions in a matter of minutes. Thus, it is possible to monitor their (n-Bu)3SnH reduction directly in the NMR tube and follow the kinetics of their dechlorination. 

Early NMR work by Roberts and coworkers51-53 showed that allyl Grignard reagents (16) are of the a type in which the metal migrates rapidly from one terminus to the other. This result was confirmed by more recent high resolution 13C NMR work of Schlosser and Stahle54. 

C2-symmetric species, which can produce isotactoid and isotactic polymers, are obtainable by occupation of one and two vicinal positions.123 An easy switch between these three polymerization modes has recently been proposed on the basis of a high-resolution 13C NMR microstructural analysis.119d... 

Applications of High-Resolution 13C-NMR and Magic-Angle Spinning NMR to Reactions on Zeolites and Oxides... 

No X-ray crystallographic studies of azo pigment lakes have as yet been reported, but solid state high resolution 13C-NMR spectroscopy was used to demonstrate that P.R.57 1 also exists in the keto-hydrazone form [9]. 

IR and visible near-IR absorption, NMR, ESR and X-ray diffraction. It was emphasized that solid-state high-resolution 13C NMR spectroscopy is a powerful tool for the structure analysis of polydiacetylenes. THY is particularly attractive because of its potential for forming the polydiacetylene ladder polymer. 

High-resolution 13C NMR studies have been conducted on intact cuticles from limes, suberized cell walls from potatoes, and insoluble residues that remain after chemical depolymerization treatments of these materials. Identification and quantitation of the major functional moieties in cutin and suberin have been accomplished with cross-polarization magic-angle spinning as well as direct polarization methods. Evidence for polyester crosslinks and details of the interactions among polyester, wax, and cell-wall components have come from a variety of spin-relaxation measurements. Structural models for these protective plant biopolymers have been evaluated in light of the NMR results. 

Schaefer J, Stejskal EO (1979) High-resolution 13C NMR of solid polymers, in Levy GC (ed) Topics in Carbon-13 NMR spectroscopy, Wiley, New York, vol 3... 

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... 

Fig. 1. Pulse sequences for high-resolution 13C NMR. I. Single pulse sequence for DD/MAS without CP. II. Pulse sequence for CP/MAS. III. Pulse sequence for longitudinal and transverse relaxation. See the text for detail...

Fig. 3. Mass fractions of crystalline, rubbery, and crystalline-amorphous interfacial phases of bulk polyethylene as a function of molecular weightMv. O data by broad-line JH NMR analysis. data by high-resolution 13C NMR analysis...

Examined are two samples that contain 2.2 mol % of ethyl side groups with molecular weights of 16,000 and 400,000 (samples PI6 and P420, respectively). The concentration of ethyl branches was determined by standard high-resolution 13C NMR methods [80-82]. These samples were crystallized from the melt by quenching at -78 °C. 

Lyerla et al. measured Tic over a wide temperature range from room temperature down to 105 K [94], and concluded that Tic s of not only CH3 but also CH resonances depend on CH3 rotational motion, and that the broadening of the CH3 resonance below -100 °C is also due to modulation of CH3 rotational motion at the frequency of proton nutation in the presence of the decoupling field. Gomez et al. have also reported solid-state high-resolution 13C NMR spectra of isotactic polypropylenes [95]. They used samples characterized by X-ray crystallography and reconfirmed the results obtained by Bunn et al. 

On the other hand, in the solid-state high resolution 13C NMR, elementary line shape of each phase could be plausibly determined using magnetic relaxation phenomenon generally for crystalline polymers. When the amorphous phase is in a glassy state, such as isotactic or syndiotactic polypropylene at room temperature, the determination of the elementary line shapes of the amorphous and crystalline-amorphous interphases was not so easy because of the very broad line width of both the elementary line shapes. However, the line-decomposition analysis could plausibly be carried out referring to that at higher temperatures where the amorphous phase is in the rubbery state. Thus, the component analysis of the spectrum could be performed and the information about each phase structure such as the mass fraction, molecular conformation and mobility could be obtained for various polymers, whose character differs widely. 

From this chapter, it is clear that high resolution 13C NMR spectroscopy has made a large number of contributions to our knowledge of the structure of vulcanised crosslinked elastomers as well as the mechanism by which the vulcanisation process occurs. It is anticipated that further NMR measurements of these systems will continue to generate new structural and mechanistic information. 

Sacchi, R., Medina, I., Aubourg, S.P., Guidicianni, I., Paolilli, L. and Addeo, F. (1993) Quantitative high resolution 13C NMR analysis of lipids extracted from the white muscle of Atlantic tuna (Thurmus alalumga). J. Agric. Food Chem., 41, 1247-1253. 

In the 13C-NMR spectra, PEG gives a singlet signal at 8 71.5 ppm due to the inner chain carbons 228). In the conformational studies of PEG-bound sequences of ala-methiein, this signal has been eliminated from the spectrum by making use of a double resonance experiment by selective saturation of the methylene carbons 209). Distinct differences between random-coil and a-helical conformations were observed from these high-resolution 13C-NMR techniques. 

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