C-1 resonance

Similarly, the C-1 resonance of an axial anomer is shielded relative to that of its eq.uatorial isomer. Also very distinctive are signals due to the carbon of a primary alcohol group (C-6, in the region of 6O-65 p.p.m.) and to the carboxyl group of an uronic acid moiety. Typically, as seen in Fig. 1, the carboxyl C=0 resonance is in the region of 1T5 p.p.m. although, as noted below (see Fig. 3), it is strongly pH dependent. 

Figure 15b shows a solid-state spectrum recorded under conditions such that only the mobile portions of the solid PDHS sample are observed. In this polymer (as previously indicated), the mobile portion of the sample consists of the locally disordered phase II and any amorphous material to the extent that it exists. The chemical-shift pattern for the carbons agrees very well with the solution spectrum (Figure 15a). Because carbon resonances are very sensitive to bond conformation (22), this result demonstrates that the phase II portion of the sample has the same average chain conformation as the polymer chains in solution. Although these NMR data permit a comparison of local bond conformations, they do not provide an indication of the more global chain dimensions. Figure 15b shows increased line widths for the carbons near the silicon backbone, with the C-1 resonance almost broadened into the baseline. This broadening reflects the severe restriction of motion near the backbone.

The three ring protons of the epoxide group are non-equivalent and appear as three distinct multiplets in the chemical shift range from 2.3 to 3.8 ppm delta. The two protons bonded to C-1 resonate at higher field than the proton attached to C-2. The appearance and chemical shifts of these bands are readily recognizable and quite characteristic of this group. 

Aregic PVF, regiosequence distributions, 160-63 Aromatic C-1 resonance, epimerized isotactic PS, 202-11 Atactic polypropylene, 3C spectra, 7 Attached proton test (APT), optimizing sensitivity, 99... 

C N.m.r. spectroscopy has been used in correlation with rates of a second-order S i2 inversion occurring at an a-pyranosyl bromide using tetraethylam-monium chloride the introduced chlorine causes a shift in C-1 resonance which was found to be proportional to In k (the rate constant) in the case of glucosyl halides but no useful correlation was noted for the galactosyl series. 

Aromatic C-1 Resonance. Figures 1-6 show aromatic C-1 carbon resonance patterns observed for various epimerized isotactic polystyrene samples. The patterns are easily divided into six resonance areas, that are designated A-F in order of increasing field. Areas A, C and E are clear in these Figures while areas B, D and F are cross-hatched. Except for the resonance pattern observed for atactic polystyrene (Figure 6), the resonances appear to be assignable as follows ... 

The C-1 resonance of starch between 98 ppm and 104 ppm, and the methylene carbon peak of PVOH between 40 ppm and 49 ppm, were monitored in the determinations. For the raw materials, the pure blend components and all the blends, the decay was sufficiently explained by a single-exponential decay function (Eq. (21.1)), resulting in a single for each material. The values of the relaxation times are listed in Table 21.3. 

Figure 8 represents one of the c-nmr spectra of heteropolysaccharides consisting of 3-deoxygenated and non-deoxygenated (l->6)-a-D-gluco-pyranan units obtained via copolymerization of [6] and [10].All peaks were superimposable on peaks of one or the other homopolymers. The a-C-1 resonance of each structural unit was completely separated from the other, and the copolymer compositions could be estimated from their area ratios. In the benzylated precursors, some of the resonances were split into two peaks whose intensity varied with copolymer compositions. The splittings are due to diad sequences between the two crossover units. This is evidence of randomly distributed copolymers. These homo-and heteropolysaccharides will serve as a tool to investigate properties and functions. 

Nuclear magnetic resonance analysis of Rosa glauca araban has provided additional evidence that the arabinosyl residues are a-5-linked and in the furanose configuration. The C-1 resonance expected of a-arabinofuranosyl residues, but not the C-1 resonances expected of the P-arabinofuranosyl or a- and P-arabinopyranosyl residues, was detected by C-NMR analysis 68b). The proton NMR spectrum is consistent with a- or P-furanosyl residues and P-pyranosyl residues, but not with a-pyranosyl residues 68b). The a-anomeric nature of these linkages is confirmed by the negative optical rotations, from —181 to —108, exhibited by such arabans 11, 68b). 

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