Unprotonated carbons

Fig. 16 Amplitude of the oscillations, a, of the phenyl rings and carboxyl groups protonated carbons, unprotonated carbons and O carboxyl carbons (from [12])...

In addition to the complexes listed in Table VII, we have used 13C NMR to determine the structure of the product of the reaction of (CDT)Ni with 2,3-dimethylbutadiene (65). The spectrum (-40°C) consists of six signals—two unprotonated carbon atoms at 102.3 and 101.7 ppm, two methylene carbon atoms at 61.1 and 48.4 ppm, and two methyl carbon atoms at 21.8 and 19.4 ppm. A determination of J(CH) for the methylene C atoms gave values of 156 and 157 Hz (both 3 Hz), clearly indicating that they are both sp2-hybridized and thereby eliminating structures such as 20b. The spectrum is consistent with a pseudotetrahedral arrangement of the two diene molecules about the nickel atom (20a). 

An unprotonated carbon simply shows one magnetization vector, which precesses at the Larmor frequency (i.e., it always points along the F axis). A normal peak is recorded at time t = 1/7. 

Intermolecular dipolar relaxation. Nearby protons on other molecules, including solvent, will not contribute significantly to the relaxation of protonated carbons, because of the r dependence deduced above. They do have a detectable influence on unprotonated carbons, however, typically contributing 0.1 Hz to 1/Ti. They can also influence the proton resonances, especially if they are held fairly close to the proton in question by, for example, some polymer entanglement. In this case f(t) will include not only any angular... 

Figure 3.42 (a) H and (b) NMR spectra of poly(1,4-phenylene ether sulfone) in deuterated dimethyl-sulfoxide, DMSO-de. Spectrum (b) shows the NOE that occurs on proton decoupling of the 0 spectmm. The peaks for the protonated carbon atoms 2 and 3 ate enhanced by the NOE over the signals from the unprotonated carbon atoms 1 and 4. The peak in the proton spectrum at 3.3 ppm is due to water in the solvent the peak at 40 ppm in the C spectrum is due to natural C in the solvent. (From Williams, E.A. Characterization of Materials, Part I., 1992. Copyright Wiley-VCH Verlag GmbH Co. KGaA. Used with permission.)... 

The DEPT 135 spectrum on page 628 shows the six aromatic C—H and the aliphatic CH3 groups. There are no CH2 groups. Since the HETCOR spectrum was not included in the problem, the best we can do is to make as many assignments as possible. The normal carbon spectrum provides some chemical shifts for the unprotonated carbon atoms. 

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