Carbon splitting

Separation of raw feedstock. The pyrolysis of petroleum feedstream is carried out at 650-900°C at normal pressure in the presence of steam. The so-called steam-cracking process involves carbon-carbon splitting of saturated, unsaturated and aromatic molecules. The following steam-cracker fractions are used as raw materials to produce hydrocarbon resins. 

Why aren t C signals split by nearby carbon atoms Recall from Section 14.6 that splitting occurs when two NMR active nuclei— like two protons—are close to each other. Because of the low natural abundance of C nuclei (1.1%), the chance of two C nuclei being bonded to each other is very small (0.01%), and so no carbon-carbon splitting is observed. 

A set of n nonequivalent protons on the same carbon or adjacent carbons splits an NMR signal into n + 1 peaks. 

Fig. 20.2 shows the NMR spectra for the PVA in (A) the solution (B-D) gel and (E) solid states as measured by solution and solid-state NMR methods [16]. The NMR spectrum for the PVA aqueous solution obtained by the solution C NMR method (Fig. 20.2(A)) shows each of the signals for the CH and CH2 carbons split into multiple peaks due to its stereochemical configuration. The triply split peaks for the CH carbon are assigned to the mm, mr and rr triads from high frequency [17-19] and, furthermore, each of the triad peaks splits into pentad peaks. The split peaks for the CH2 carbon come from tetrad tacticity. In the solution NMR spectrum for the PVA gel shown in Fig. 20.2(B), the signal for the CH carbon splits into three peaks due to triad tacticity. The signals for the CH and CH2 carbon become broader as compared with those for the PVA solution. This is caused by the...

Until recently 1 3C nmr studies of nucleic acids have not received the same attention as those of nucleosides and nucleotides. Poly-uridylic acid (poly U), polyadenylic acid (Poly ), and unfractionated baker s yeast transfer ribonucleic acid (tRNA) have been investigated by 13C nmr techniques (Table 11 Mantsch and Smith, 1972 Komoroski and Allerhand, 1972, 1974). Assignments for uridine monophosphates were based on changes in phosphorus-carbon splittings and on changes in the chemical shift of approximately 2-5 ppm on the phosphorylated carbon, which was caused by the deshielding effect of the phosphate group (Mantsch and Smith,... 

It has been proposed that the monohydroxylate is further hydroxylated to yield a dihydroxylate. A des-molase capable of attacking either 20- or 22-hydroxy derivatives yields, by splitting the side chain, pregnenolone and isocaproic aldehyde, which is converted to isocaproic acid. It may be significant that the carbon-to-carbon split that is catalyzed by desmolase is sensitive to ACTH, LSH, HCG, and angiotonin II (which... 

The molar ratio between the oxygen added to the polymer and the carbon split out from it is higher than 0.5 and is equal to 0.55-0.75 (it decreases with the time of oxidation). On the basis of these data, the opinion has been expressed [44] that hydroxyl groups, bonded to a silicon atom, and siloxane bonds are formed at the site of splitting out of methyl groups. 

This is seen in the spectrum of 2-butanone (Fig. 8.46) where the four different types of carbon atoms produce four separate resonances. Note that three peaks near 8 79.5 ppm in the spectrum are associated with the solvent, deuterochloro-form, CDCI3. The single carbon atom of this solvent produces more than one peak because of deuterium-carbon splitting, which is not eliminated by the broadband decoupling technique. Deuterium has a nuclear spin, of 1, so applying Equation 8.10 predicts a triplet for the carbon atom, as is observed experimentally. Rather than provide the broadband-decoupled spectra themselves, we will simply give the chemical shifts for the various carbon atoms of the starting materials and products in this textbook. 

In CH3CH2CH2Br, the n protons on one adjacent carbon and the m protons on the other adjacent carbon split the observed signal into n + m +1 peaks. In other words, the 3 Ha protons and 2 He protons split the NMR signal into 3 + 2 + 1 = 6 peaks, as shown in the sextet in Figure 14.8. 

Scott s results were identical with Shemin s findings on administration of [5- C]ALA. The spectrum of the enriched B,j had only seven signals, with the expected carbon-carbon splitting patterns at 187.2, 186.7, 183.6, 180.7, 113.2, 110.3, and 1(X).4 p.p.m. shifts downfield from hexamethyidisilazane... 

Think of each C-H bond as a phone link. In the coupled spectrum, each H is talking to the nearest carbon, splitting the carbon signal through this "phone link." To make a decoupled spectrum, we produce lots of static on the phone line so each carbon cannot hear the H s attached to it. Consequently, each carbon shows up as a singlet (one peak). You will probably never see a coupled... 

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