NMR 13C Spectroscopy

C NMR spectroscopy. 13C NMR resonances for both carbonyls of the TV-acyloxy-V-alkoxyamides and that of the parent hydroxamic ester are given for most compounds in Table 2. 

Spectroscopic observations ofalkylcarbonium ions in strong acid solutions, 4, 305 Spectroscopy, 13C NMR. in macromolecular systems of biochemical interest, 13, 279 Spectroscopy of substituted phenylnitrenes, kinetics and 36, 255... 

C NMR Spectroscopy. 13C NMR measurements were carried out using a JEOL JMN-GSX 400 spectrometer for quantitative analysis in order to examine the amount of bound phenol in the phenolated SEL s. The analysis was conducted in DMSO-dg by using gated decoupling technique. 

Solvolytic reactions, medium effects on the rates and mechanisms of, 14, 1 Spectroscopic detection of tetrahedral intermediates derived from carboxylic acids and the investigation of their properties, 21, 37 Spectroscopic observations ofalkylcarbonium ions in strong acid solutions, 4, 305 Spectroscopy, 13C NMR in macromolecular systems of biochemical interest, 13, 279 Spectroscopy of substituted phenylnitrenes, kinetics and, 36, 255 Spin alignment, in organic molecular assemblies, high-spin organic molecules and,... 

Heymann et al. [255] and Smith et al. [256] reported the synthesis of C70O 82 by photooxygenation. Irradiation of an oxygenated toluene solution of C70 and rubrene as a sensitizer resulted in the formation of a nearly 1 1 mixture of two C70O isomers 82a and 82b that can not be separated (Fig. 31). The structures of 82a and 82b were elucidated by UV-vis spectroscopy, 13C-NMR studies as well as 3He NMR studies. No evidence for the formation of isomers 82c and 82d was found. 

A-2-Thiazoline-5-one may exist in three tautomeric forms (Scheme 108). The tautomeric equilibrium has been studied by H NMR (446. 453. 457. 464), infrared (453. 464-466). and ultraviolet (453, 464) spectroscopies 13C NMR data would be very instructive since model compounds for the three tautomers are now available. Polar solvents favor the enolic (211b) and the mesoionic (211c) forms (Table VII-12), the later being even more favored by high dilution (464). The percentage of the enol... 

Nuclear magnetic resonance (NMR) spectroscopy (Section 14.1) A type of spectroscopy that uses transitions between the energy states of certain nuclei when they are in a magnetic field to supply information about the hydrocarbon part of a compound. There are two NMR techniques that are of most use to organic chemists proton magnetic resonance (lH-NMR) spectroscopy, which provides information about the hydrogens in a compound, and carbon-13 magnetic resonance spectroscopy (13C-NMR), which provides information about the carbons in a compound. 

A survey of characterization methods for linear and branched nonionic polyacrylamides is given in reference 5. Gel-permeation chromatography, diffusion and sedimentation, intrinsic viscosity, and light scattering are discussed emphasizing some difficulties encountered in obtaining consistent data. Characterization of anionic polyacrylamides used in oil recovery by ir spectroscopy, 13C-nmr, tga, and x-ray diffraction is described in reference 8. 

Interactive to learn to utilize 13C NMR spectroscopy to deduce molecular structures. 

The information derived from 13C NMR spectroscopy is extraordinarily useful foT structure determination. Not only can we count the number of nonequivalent carbon atoms in a molecule, we can also get information about the electronic environment of each carbon and can even find how many protons each is attached to. As a result, we can answer many structural questions that go unanswered by TR spectroscopy or mass spectrometry. 

Most of the reported 1,2,5,6-tetrazocine systems probably do not exist in the monocyclic form but rather as the tetraazapentalene betaine structure (see Introduction) 2 3 7"13 for the tetra-phenyl-substituted system, the compound does actually exist as the mesoionic tetraphenyl-[1,2.3]triazolo[l,2-h][l,2,3]triazole, as determined by H and 13C NMR spectroscopy.15 The following syntheses arc therefore questionable. 

The free ligands were obtained by visible photolysis in acetonitrile and were characterized by elemental analyses and H- and 13C-NMR spectroscopies. Low-temperature reduction in ESR tubes also provided the green Fe1 19e complexes which gave the characteristic 3g values typical of the rhombic distortion of Fe1 [77],... 

Sometimes decomposition reactions can be avoided by carrying out diazotizations in concentrated sulfuric acid. By this method Law et al. (1991) obtained the 1,5-bisdiazonium salt (incorrectly called tetrazonium salt) of l,5-diamino-4,8-dihy-droxy-anthraquinone, which is deprotonated to 2.28. The structure was verified by cross-polarization magic angle spinning (CPMAS) 13C NMR spectroscopy. 

The thermal imidization of a polyamic acid film (PMDA-ODA or BPDA-ODA) obtained by casting an NMP solution leads to an amorphous polyimide. Two different teams have shown that a polyamic acid solutions in NMP heated at 200°C for a short time (20 min) gives polyimide particles fully cyclized and highly crystalline, as shown by X-ray diffraction and solid 13C NMR spectroscopy.151152 The chemical imidization of the same solution gives only amorphous particles. The difference between the cyclization of a solution and a casted film in the same solvent is intriguing. In the case of the solution, the temperature and the heating time are lower than in the case of the casted film as a consequence, a less organized structure would be expected for the particle. 

A number of analytical techniques such as FTIR spectroscopy,65-66 13C NMR,67,68 solid-state 13 C NMR,69 GPC or size exclusion chromatography (SEC),67-72 HPLC,73 mass spectrometric analysis,74 differential scanning calorimetry (DSC),67 75 76 and dynamic mechanical analysis (DMA)77 78 have been utilized to characterize resole syntheses and crosslinking reactions. Packed-column supercritical fluid chromatography with a negative-ion atmospheric pressure chemical ionization mass spectrometric detector has also been used to separate and characterize resoles resins.79 This section provides some examples of how these techniques are used in practical applications. 

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