NMR, carbon

3 Carbon-13 NMR. - Specific NMR data of 1,3,2-oxazaphospholidine derivatives (79) are reported. The use of phosphorus J-scaled proton-carbon 2D NMR for coupling constant measurements is also reported, for example in the J-scaled correlation spectra of the DNA aptamer 

Protonation of the amino group produces expected opposite shifts of carbon signals of 2-aminopyrroles in DMSO/ TEA 1996JHC161 C-2 resonances shift upfield by 3-5 ppm (7-11 ppm in the case of AT-substituted derivatives), whereas C-3 carbons become deshielded and undergo downfield shifts of 1.5-2.5 ppm (5-9 ppm in AT-substituted derivatives) (Table 12). The magnitudes of these effects are smaller than those observed with 3-aminopyrroles, but no explanation has been offered for this difference. Notably, 2- and 3-aminopyrroles in pure TEA are protonated at the 5- and/or 3-positions of the ring, confirming similar behavior. 

As in the case of protons, /3-carbon chemical shifts for meta- and / zra-substituted 1-phenyl, 1-benzyl, 1-benzoyl, and l-(2-phenylethyl)pyrroles correlate remarkably well with t and ay parameters, and much better than a-carbon shifts 2000JHC15 . Plots of the same chemical shift data against other substituent correlation parameters, such as Taft s a-substituent constant, gave less satisfactory correlations. 

Protonation of 2-aminoindole and 2-amino-3-phenylindole occurs at C-3 and results in a downfield shift of the C-2 carbon signal in DMSO/TFA of 25.6 and 30.4 ppm, respectively, whereas the C-3 resonance shifts upfield by 39.6 and 42.1 ppm 2000T5177 . With those 2-aminoindoles in which protonation occurs at the amino group the aromaticity of the indole ring is retained and an opposite trend is observed the C-2 carbon signals shift upfield by 26.5 and 28.7 ppm for 2-amino-3-carboethoxyindole and 2-amino-3-acetylindole, respectively, whereas the C-3 carbons are only slightly deshielded ( 2ppm). 

Amino group protonation in 2-phenyl-, 2-carboethoxy-, and 2-(4-chlorophenyl)-3-aminoindoles results in an upfield shift of the C-3 carbon of 18.6-28.6 ppm and a downfield shift of the C-2 carbon of 6.9-11.6 ppm. 

Carbons carrying the azido group in 2-azido-l-methylindole and 3-azido-l-methylindole are deshielded relative to 1-methylindole (6.7 and 7.1 ppm, respectively), whereas an opposite shielding effect is seen on the adjacent carbon AS —12.9 for C-3 in 2-azido-l-methylindole and -10.6 for C-2 in 3-azido-l-methylindole) 1995G151 . The remainder of the carbon signals are virtually unaffected. 

In comparison with the carbocyclic analogue indene, one can see the effect of the heteroatom most strongly in the )S-carbons C-3, C-3a, and C-7 with upheld shifts of 29.6, 16.7, and 12.4 ppm, respectively. Only moderate effects (0.1-9.5 ppm) are seen at the other carbons 87MRC377 . Relative 

Pyrroles end their Senzo Derivatives Structure Table 18 Proton NMR data 8, ppm) for indoles. 

Pyrroles and their Benzo Derivatives Structure Table 22 Carbon-13 NMR data d, ppm) for pyrroles. 

Pyrroles and their Benzo Derivatives Structure Table 23 (continued) 

Carbon-13 NMR has established itself as an indispensable tool for structure determination in the area of carbazole-containing natural products, and the reader is encouraged to consult the articles by Chakraborty 87FORi59, 9lFOR7l for a more exhaustive treatment of carbazole alkaloids. A shorter overview of the typical C resonances for carbazoles is included in Table 24. 

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Bouquet, M. and A. Bailleul (1986), Routine method for quantitative carbon 13 NMR spectra editing and providing structural patterns. Application to every kind of petroleum fraction including residues and asphaltenes . Fuel, Vol. 65, p. 1240. 

Breitmaier E and Voelter W 1986 Carbon-13 NMR Spectroscopy High Resolution Methods and Applications in Organic Chemistry (New York VCH)... 

Maler L, Lang J, Widmalm G and Kowalewski J 1995 Multiple-field carbon-13 NMR relaxation investigation on melezitose Magn. Reson. Chem. 33 541-8... 

Tetramethylsilane (TIMS) (Section 13 4) The molecule (CH3)4Si used as a standard to calibrate proton and carbon 13 NMR spectra... 

Proton and carbon-13 nmr spectroscopy provides detailed information on all types of hydrogen and carbon atoms, thus enabling identification of functional groups and types of linkages ia the lignin stmcture. Detailed a ssignments of signals ia proton and carbon-13 nmr spectra have been pubHshed... 

Carbon-13 nmr. Carbon-13 [14762-74-4] nmr (1,2,11) has been available routinely since the invention of the pulsed ft/nmr spectrometer in the early 1970s. The difficulties of studying carbon by nmr methods is that the most abundant isotope, has a spin, /, of 0, and thus cannot be observed by nmr. However, has 7 = 1/2 and spin properties similar to H. The natural abundance of is only 1.1% of the total carbon the magnetogyric ratio of is 0.25 that of H. Together, these effects make the nucleus ca 1/5700 times as sensitive as H. The interpretation of experiments involves measurements of chemical shifts, integrations, andy-coupling information however, these last two are harder to determine accurately and are less important to identification of connectivity than in H nmr. 

The syndiotactic polymer configuration is not obtained in pure form from polymerizations carried out above 20°C and, thus has not been a serious concern to most propylene polymerization catalyst designers. Eor most commercial appHcations of polypropylene, a resin with 96+% isotacticity is desired. Carbon-13 nmr can be used to estimate the isotactic fraction in a polypropylene sample. Another common analytical method is to dissolve the sample in boiling xylene and measure the amount of isotactic polymer that precipitates on cooling. 

J. B. Stothers, Carbon-13 NMR Spectroscopy, Academic Press, Inc., New York, 1972. 

The spin-lattice relaxation time, T/, is the time constant for spin-lattice relaxation which is specific for every nuclear spin. In FT NMR spectroscopy the spin-lattice relaxation must keep pace with the exciting pulses. If the sequence of pulses is too rapid, e.g. faster than BT/max of the slowest C atom of a moleeule in carbon-13 resonance, a decrease in signal intensity is observed for the slow C atom due to the spin-lattice relaxation getting out of step. For this reason, quaternary C atoms can be recognised in carbon-13 NMR spectra by their weak signals. 

Chemical shift (Section 13.4) A measure of how shielded the nucleus of a particular atom is. Nuclei of different atoms have different chemical shifts, and nuclei of the same atom have chemical shifts that are sensitive to their molecular environment. In proton and carbon-13 NMR, chemical shifts are cited as 8, or parts per million (ppm), from the hydrogens or carbons, respectively, of tetramethylsilane. 

H.-O. Kalinowski, S. Berger and S. Braun, Carbon-13 NMR Spectroscopy, Wiley, Chichester, 1988. 

Figure 13.6 Carbon-13 NMR spectra of 1-pentanol, CH3CH2CH2CH2CH2OH. Spectrum (a) i a single run, showing the large amount of background noise. Spectrum lb) is an average of 200 runs.

Figure 13.8 Carbon-13 NMR spectra of (a) 2-butanone and (b) para-bromoacetophenone.

W. Wehrli and T. Wirthlin, Interpretation of Carbon-13 NMR Spectra, Heyden and Son, London, 1978. 

Using proton NMR of solutions, the composition of polymers can be analyzed.47 Carbon-13 NMR spectroscopy is a useful tool for studying the sequence length of segments in copolymers and thereby determining the blockiness of the copolymer. With solid-state NMR, the mobility of chain segments can be studied and the crystallinity determined. 

Carbodiimides, 81 Carbodiimidization, 226-227 Carbon-13 NMR spectroscopy. See 13C NMR spectroscopy Carbon-carbon structure, 4 Carbonyl-containing polyester polyols,... 

Randall, J. C., Polymer Sequence Determination. Carbon-13 NMR Method Academic Press New York, 1977. 

Unkefer CJ, RE London (1984) In vivo studies of pyridine nucleotide metabolism in Escherichia coli and Saccharomyces cerevisiae by carbon-13 NMR spectroscospy. J Biol Chem 2311-2320. 

Shaw, C.F. Ill, Eldridge, J. and Cancro, M.O. (1981) Carbon-13 NMR studies of aurothioglucose ligand exchange and redox disproportionation reactions. Journal of Inorganic Biochemistry, 14, 267-274. 

Isab, A.A. (1992) The carbon-13 NMR study of the binding of gold(I) thiomalate with ergothionine in aqueous solution. Journal of Inorganic Biochemistry, 45, 261-267. 

Several trends have emerged in the extensive carbon-13 NMR spectroscopy data that have been accumulated for sulfones and sulfoxides. Based on many studies of cyclic systems—particularly five- and six-membered ring sulfur compounds—these trends were shown to generally apply equally to both the cyclic and acyclic systems . Thus (a) oxidation of a sulfide to a sulfone results in a 20-25 ppm downfield chemical shift for sp -hybridized a-carbon atoms and 4-9 ppm upfield shift for / -carbons , and (b) there is very little difference between the chemical shifts of a-carbon atoms of sulfones and sulfoxides despite the difference in the inductive effects of these two functional groups . A difference is observed, however, in the H chemical shift of related cyclic sulfoxides and sulfones . 

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