Poly chemical shift

Fig. 12.13C-NMR spectrum of erythrodiisotactic poly(l,2-dimethyltetramethylene) at 75.47 MHz and 303 K. a) in solution of CDC13, b) CP-MAS spectrum of the semicrystalline polymer in the bulk. Chemical shifts given at the signals refer to TMS = 0 ppm. (Ref.20))...

DSC 31 The signals of the carbons within the crystalline phase have the same chemical shifts as at 303 K. The signals of the carbons of the amorphous phase changed as can be seen most obviously at the CH3 resonances. Figure 17 shows the CP-MAS 13C-NMR spectra of the threodiisotactic poly(l,2-dimethyltetramethylene)... 

From these results it is reasonable to conclude that no inversion in the order of the chemical shifts of the tertiary carbon atoms belonging to the different triads occurs from the starting PV0CC1 to the poly(vinyl phenyl carbonate). Moreover the chemical modification of PV0CC1 by phenol does not induce any degradation of the polymer. 

All of the soluble polymers (1 and 3-6) give high resolution NMR spectra (1H, 13C, and 31P) that are completely consistent with their proposed structures. As observed for other types of poly(phosphazenes), the 31P chemical shifts of these alkyl/aryl substituted polymers are consistently ca. 15-30 ppm upfield from those of the analogous cyclic trimers and tetramers. Some important structural information is provided by 13C NMR spectroscopy, particularly for the phenyl/alkyl derivatives 3 and 4. These polymers are rare examples of phos-phazenes that contain two different substituents at each phosphorus atom in the chain. Thus, they have the possibility of being stereoregular. The fact that the structures are completely atactic, however, is confirmed by the observation of three doublets in the P-Me region of the 13C NMR spectrum (ca. 22 ppm) in a 1 2 1 intensity ratio. 

This first example of the utility of quadrupolar nuclei as sources of information about nano-semiconductors showed that MAS-NMR could identify a poly type that is unstable in the bulk. A second example will show that information about changes in the electronic structure of nanocrystals as a function of synthesis and treatment conditions, as well as information about different polytypes, can be obtained via measurement of Knight shifts and chemical shifts. In this extensive study 69Ga... 

The ability of NMR to distinguish poly types will be greatly aided, as it was in the recent case discussed of SiC, by theoretical calculations of chemical shifts and CS A values (and for quadrupolar nuclei, NQCC values). Also, MAS-NMR may succeed in identifying low levels of polytypes or new ones that have not been seen by diffraction methods. 

A first generation poly(amido amine) dendrimer has been functionalized with three calyx[4]arenes, each carrying a pyrene fluorophore (4) [30]. In acetonitrile solution the emission spectrum shows both the monomer and the excimer emission band, typical of the pyrene chromophore. Upon addition of Al3+ as perchlorate salt, a decrease in the excimer emission and a consequent revival of the monomer emission is observed. This can be interpreted as a change in the dendrimer structure and flexibility upon metal ion complexation that inhibits close proximity of pyrenyl units, thus decreasing the excimer formation probability. 1H NMR studies of dendrimer 4 revealed marked differences upon Al3+ addition only in the chemical shifts of the CH2 protons linked to the central amine group, demonstrating that the metal ion is coordinated by the dendrimer core. MALDI-TOF experiments gave evidence of a 1 1 complex. Similar results have been obtained for In3+, while other cations such as Ag+, Cd2+, and Zn2+ do not affect the luminescence properties of... 

Finally, dipolar and chemical shift correlation (DIPSHIFT) NMR was used to investigate the molecular motion and dynamics of the immobilized alkyl ligands of poly(ethylene-co-acrylic acid) stationary phases [164]. Through the measurement of the dipolar couplings, it was possible to discern the geometry of motion of... 

Figure 4 Detail of the amide carbonyl resonances in the C-NMR spectrum (100 MHz) of poly (Lys-25) in 70% H2O/30% D2O solution. The spectrum was recorded on a Varian INOVA 400 NMR spectrometer. Chemical shifts were referenced to external tetramethylsilane.

The magnitude of the chemical shift anisotropy depends on the bonding situation and the nucleus gyromagnetic ratio. Since the bonds formed by lithium in organolithium compounds or other lithiated systems are mainly ionic, the anisotropy of the lithium chemical shift is generally small. It is more pronounced for Li than for Li. Li spectra are dominated by the quadrupolar effect and the CSA contribution to the Li lineshape is often negligible. Exceptions are compounds with poly-hapto bound lithium, such as... 

Other hand, the spectrum of the mixture of 2f and poly(d-VL) [Fig. 46 (III)] showed the signals at the original chemical shifts [Fig. 46 (I)] in addition to the shifted signals, where the relative intensity ratio of the shifted signals to the original signals was 4 6. These observations indicate that 31 interacts more strongly with 6-VL than with poly(6-VL), while 3f possibly interacts almost equally with 6-VL and poly(6-VL). 

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