Methylene carbon resonances

C NMR of linear cross-linked PS. The proton decoupled 13C NMR spectra of linear and 1% cross-linked PS at 75 MHz in chloroform are illustrated in Figure 3. These spectra are similar to those for linear and cross-linked chloromethylated PS previously reported at lower field (14), although we have been able to resolve more structure in tHe" aliphatic and aromatic regions here. The quarternary and methylene carbon resonances at about 146 ppm and between 40 and 50 ppm respectively, are the most strongly affected by stereochemistry (20). The ortho and meta resonances at 128.4 ppm show partially resolved structure in the linear PS, as does the para carbon at 126.1 ppm. The methine resonance at... 

These derivatives are soluble in an acetone/water mixture with their p i values similar to that of PIDAA. The phenylene analogs are similar to EDTA except that the two nitrogens are bridged by aromatic rings. These derivatives are soluble in acetone/water. They were characterized by measuring their H- and C-nuclear magnetic resonance (NMR) spectra and Fourier transform infrared (FTTR) spectra. All the PIDAA derivatives showed a peak near 53 ppm for the methylene carbons in carbon NMR spectra. The methylene carbon resonance appears around 44 ppm in the NPG derivative. Thus offers an easier way to characterize these materials. The FTNMR data are listed in Table 1 below. 

We observe the a-methylene carbons of the methyl tetrahydro-furanium ion, the a-carbons of the two types of propagating chain heads, the macroion and the macroester (17). The observation of the a-methylene carbon resonances of the acyclic tertiary oxonium ion provides a direct proof of chain transfer reaction in THF polymerization. 

T. K. Wu We tried to determine the amount of dormant species in homopolymerizations. We can measure the ratio of "exocyclic" vs. "endocyclic" methylene carbon resonance, and if the ratio is not exactly 1 to 2 we can get an estimate of the concentration of dormant ion. 

The Tetrad Chemical Shift Sequence with Respect to an Increasing Field Strength for Some Representative Vinyl Polymer Backbone Methylene Carbon Resonances... 

Empirically determined chemical shift additivity parameters have been determined- for diene-type polymers. The shift contribution of a quaternary carbon which is fllto the carbon in question was not determined by those authors. However, using their additivity parameters and the shift positions of the ( carbons in Figure 8, a value of +15.4 ppm can be estimated for the contribution of a neighboring (0() quaternary carbon. Using this value, the shift positions of the carbons in structures VII and VIII are calculated as shown. If the first 1,2 unit were on the chain in a 2,1 manner, the methylene carbon resonance would be at a considerably higher field, but it would be difficult to estimate its position with any certainty because the quaternary effect... 

Ipsenol has two methyl groups that appear as a triplet at 0.93 ppm in the proton spectrum. A closer look, however, at the inset reveals that it is a pair of coincidental doublets. Before moving on to the next section, consider the following question can the olefinic methylene carbon resonances be assigned on the basis of combined information from COSY and HMQC ... 

The COSY spectrum for caryophyllene oxide can be understood more clearly when interpreted in conjunction with the information from an HMQC spectrum (Figure 5.17). From the DEPT spectrum (see Figure 5.15), we already know that caryophyllene oxide has three methyl carbon resonances (16.4, 22.6, and 29.3 ppm), six methylene carbon resonances (26.6,29.2, 29.5, 38.4, 39.1, and 112.0 ppm), three methine carbon resonances (48.1, 50.1, and 63.0 ppm) and three quaternary carbon resonances (33.3,59.1, and 151.0 ppm)... 

Recently Roberts and Olah and their coworkers (Staral et al., 1978) reported further investigation of under stable ion conditions by C-nmr spectroscopy which indicates the coexistence of at least two structural isomers of in rapid equilibrium with one another. The ion mixture was prepared from cyclopropylcarbinol-4- C (43 % C) in a SbEs-SOjClF-SOjE solution at —125°C and observed at —70 C. The spectrum displayed resonances at (ref. TMS) S 107.56 and 57.48 which may be assigned to the methine and averaged methylene carbon resonances of The label is distributed... 

Region "C" is somewhat more complicated because it consists of both methine and methylene carbon resonances. 

When a polymer is altered by chemical reaction and the process is not carried to completion, the modified units are not necessarily distributed at random through the macromolecules. The partial conversion of polyVAC to poly(vinyl alcohol) gives a product in which the residual VAC units tend to occur in blocks [82] (see chapter 2). This conclusion was reached from CNMR studies of the materials dissolved in D2O. The methylene carbon resonances were used to determine the mean lengths of sequences of VAC and of vinyl alcohol units. 

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