Carbon-13 nuclear magnetic resonance spectroscopy chemical shifts

In an attempt to relate calculated results to experimental findings for monomeric, lignin model compounds, preliminary work has compared theoretically determined electron densities and chemical shifts reported from carbon-13 nuclear magnetic resonance spectroscopy (62). Although chemical shifts are a function of numerous factors, of which electron density is only one, both theoretical and empirical relationships of this nature have been explored for a variety of compound classes, and are reviewed by Ebra-heem and Webb (63), Martin et al. (64), Nelson and Williams (65), and Farnum (66). 

Physical phenomena other than rates and equilibrium constants can be correlated by Hammett-type relationships. For example, as Figure 2.4 shows, in 13C nuclear magnetic resonance spectroscopy (called Cmr) the chemical shift of the cationic carbon in 17 is correlated by Brown s cr + values.21 And the C=0... 

Hawkes, G.E., Smith, R.A., and Roberts, J.D., Nuclear magnetic resonance spectroscopy carbon-13 chemical shifts of chlorinated organic compounds, J. Org. Chem., 39, 1276, 1974. 

DuVernet, R. and Boekelheide, V., Nuclear magnetic resonance spectroscopy ring-current effects on carbon-13 chemical shifts, Proc. Natl. Acad. Sci. U.S.A., 71, 2961, 1974. 

Evidence for the interaction between tributylamine and BN nanotubes has been obtained by nuclear magnetic resonance spectroscopy. We have studied the H and 13C NMR spectra of tributylamine-functionalized BN nanotubes in comparison with the spectra of tributylamine. We observe a small increase in the H chemical shift by 0.02 ppm in the amine-BN adduct. In the case of nC NMR spectra, we observe a significant increase in the chemical shifts of the y and S carbons by 0.4 ppm and a decrease in the chemical shift of the P carbon atom by 0.3 ppm. The chemical shift of the acarbon is also higher in the amine-BN adduct by 0.1 ppm. The changes in the H and L1C spectra of tributylamine found on interaction with BN are comparable to those reported in the literature for similar complexes.17,18... 

Carbon-13 Nuclear Magnetic Resonance Spectroscopy Carbon-13 Chemical Shifts and Coupling Constants... 

Figure 5.11. The C chemical shift values (5) for some cyclic ethers relative toTMS (5 = 0.00) in HCClj solution (after Levy, G. C. Lichter, R. L. Nelson, G. L. Carbon-13 Nuclear Magnetic Resonance Spectroscopy, 2nd edition, Wiley-Interscience, New York, 1980, p. 59).

Inasmuch as establishing the carbon framework of a molecule overcomes a major obstacle to structure determination, carbon nuclear magnetic resonance ( C-NMR) spectroscopy is potentially the most powerful spectroscopic implement for natural products characterization. The broad range of chemical shifts are valuable in determining the presence of different functional groups (49, 84, 85, 235, 321,... 

Mooney E F, Winson P H 1969 Carbon-13 nuclear magnetic resonance spectroscopy. Carbon-13 chemical shifts and coupling constants. Ann Rev NMR Spec 2 153—218... 

Roberts J D, Weigert F J, Kroschwitz J I, Reigh H J 1970 Nuclear magnetic resonance spectroscopy. Carbon-13 chemical shifts in acyclic and alicyclic alcohols. J Am Chem Soc 92 1338-1347... 

The section on Spectroscopy has been retained but with some revisions and expansion. The section includes ultraviolet-visible spectroscopy, fluorescence, infrared and Raman spectroscopy, and X-ray spectrometry. Detection limits are listed for the elements when using flame emission, flame atomic absorption, electrothermal atomic absorption, argon induction coupled plasma, and flame atomic fluorescence. Nuclear magnetic resonance embraces tables for the nuclear properties of the elements, proton chemical shifts and coupling constants, and similar material for carbon-13, boron-11, nitrogen-15, fluorine-19, silicon-19, and phosphoms-31. 

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