Methine peaks

The steric structure of poly[o-phthalaldehyde] was investigated (53). The recurring unit of the polymer was composed of cis- and/or trans-oxyphthalan rings. The content of cis- and trans-rings in the polymer was determined by comparing the methine peak areas in... 

Figure 12 shows the C CP/MAS spectra of PVA, sample I and sample II, where sample I and sample II are corresponding to PVA/PAA blends with PAA contents in monomer molar of 0.27 and 0.53, respectively. Three overlapped peaks ranged from 65 ppm to 77 ppm are attributed to methine carbon of PVA and are designated to peaks 1, 2 and 3, respectively (Fig. 13). The assignment of these three methine peaks, which had been an attractive...

Fig. 14. Plots of the relative intensities of three methine peaks in the CP/MAS spectra of sample I against the draw ratio (X), where ( ), (A) and (o) are corresponding to the data of peaks 1, 2 and 3, respectively. (Figure 3 in the original literature Q. Chen, H. Kurosu, L. Ma and M. Matsuo, Polymer, 2002, 43, 1203.)...

On the other hand, only one peak at 48.29 ppm is observed in the methylene region of Form II as shown in Fig. 11.15(b). This indicated that the sample consists of a molecular chain with an all-trans-conformation where the methylene carbons receive no y-effect. Differences in chemical sifts between Forms I and II are also observed for methyl and methine peaks although the difference is small. The methyl carbon receives one y-effect from a methine carbon in Form I, but it receives two y-effects in Form II. The methine carbon receives two y-effects from two carbons which are methylene and methyl in Form I but two methyls in Form II. 

The present study mostly confirms the results of previous assignments made by Ray et al. (22) with respect to the identification of methyl, methylene, and methine peaks. In... 

There are additional rules for assigning methylenes. Firstly, a methylene connecting only one methine peak is either one of mmm, rmi mrm, and rrr secondly, methylenes showing no cross-peak in the nietliylene-methylene corss-peak region is mrm or rrr and thirdly, a methylene connecting two methines is mmr or mrr. 

As mentioned before, two of the three peaks 3, 7, and 8 are equivalent methylene, rrr and mrm, and rrr methylene is connected to only rr methine and mnn is connected to only mr methine. Because the central methine peak has been found to be mr methine, peak 8 methylene can be assigned to rrr and 7 to mrm. Using all rules we can assign proton spectra of PVA in non-empirical manner. Table lists the results of assignment of proton spectra of PVA in D2O. 

Figure 8 shows the schematic diagram of the connectivity between rr centered methine peaks 8, 9, and 10 and methylene peaks a, b, c, g, and g". Figure 9 shows the theoretical connectivity between rr-centered pentad methine and hexad methylene. If we compare this with the experimental results, we can assign carbon-13 spectrum at the pentad-hexad level. Table II lists the results of carbon-13 resonance assignment of PVA. 

Using this assignment, we calculate the fraction of each configuration. Table III shows the fractional area of methine peaks. The best fits of Bernoulli trial, the 1st-Markov trial, and the 2nd Markov trial are also listed. The data at the triad level are also shown here. The data at the traid level are all in agreement with any statistics. However, the data at more higher level are not agreement with any statistics. The... 

The deuteriated methine carbon was shifted upheld and the intensity ratio observed for the downfield to upheld methyl peaks was 2 1. This ratio results from the fact that only one out of three exchanging methine positions is deuteriated. The upfield shift of the deuteriated methine peak towards the... 

Olah and Roberts (Olah et a ., 1978b) interpreted a small temperature dependence of the nmr spectrum of C-labclled 4117 as indicating a minor species like [124] in rapid equilibrium with the major ion [139], A splitting of 0.4 ppm between the methine peaks of two isomeric deuteriated cations observed by Saunders and Siehl (1980) and also by Roberts et al. (1984) might indicate an isotope effect on a nondegenerate equilibrium in support of this idea. 

Carbon-13 NMR can potentially give more Information about triad distribution. Several workers (10,11,18,20) have made use of this technique. The three methine peaks observed in the NMR spectra have been assigned to syndiotactic, isotactic and hetero-tactic triads. Although theoretically ddl and dll triads should be non-equivalent, only a single type of heterotactic traid peak has been found. Since the Information obtained from diad and traid distributions are mutually consistent, we consider only the existence of only a single heterotactic species. 

The DEPT spectrum shown in Figure 9.12 yields the number of protons on each of the peaks. There are three methyl groups, four methylene groups, and two methine groups. One of methine peaks appears downfield at about 124 ppm and is assigned to C6. The other methine peak is assigned to C3. The remaining carbon atom is in the double bond, and must be C7. It does not appear in the DEPT spectrum because there is no attached proton. 

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