C-NMR Chemical Shifts

Figure 6. Structural Positions (bold numbers) in the Bromocriptine Skeleton and corresponding C-13-NMR Chemical Shifts ( in italics) in ppm downfield...

Osamura, Y., Sayanagi, O., and Nishimoto, K., C-13 NMR chemical shifts and charge densities of substituted thiophenes the effect of vacant dn orbitals, Bull. Chem. Soc. Jpn., 49, 845, 1976. 

Asakura, T. Demura, M. Date, T. Miyashita, N. Ogawa, K. Williamson, M.P. NMR study of silk I structure of Bombyx mori silk fibroin with N-15- and C-13-NMR chemical shift contour plots. Biopolymers. 41 193-203 (1997). 

GEOMETRY OF a-CYCLODEXTRIN INCLUSION-COMPLEXES WITH SOME SUBSTITUTED BENZENES DEDUCED FROM C-13 NMR CHEMICAL SHIFTS ... 

Reich, H.J. C-13 NMR chemical shifts. Available from http //www.chem.wisc.edu/ areas/reich/handouts/nmr-cl3/cdata.htm [Accessed 20 January 2010]. 

Table 6 Carbon-13 NMR Chemical Shift Data of Grignard Reagents in THF at 25 C ...

This section contains the carbon-13 NMR chemical shifts of fluorinated hydrocarbons. The chemical shifts of these compounds illustrate not only that fluorine is one of the most strongly deshielding substituents in its effect on the alpha carbon (alkanes F- C =+69.9ppm, benzenes F-a C = +34.9ppm) but that fluorine 1... 

The carbon-13 NMR chemical shifts of the carbonitrile compounds contained in this section display the characteristically weak resonance of the C=N carbon over the chemical shift range from 111 to 126 ppm. The long relaxation time exhibited by the nitrile carbon often requires the utilization of relatively small pulse widths and/or the addition of a relaxation agent to the sample solution. 

As the carbon-13 NMR chemical shifts in this section illustrate, the - N02 group has a strongly deshielding effect on the adjacent carbon (C-1) of both aliphatic and aromatic compounds. The additivity constants for nitrobenzenes are ... 

The carbon-13 NMR chemical shifts presented here illustrate typical band intensities of the aromatic ketones. Depending upon their structural environment, the carbonyl (C=0) resonance appears over a chemical shift range of more than 48 ppm (167.8 - 216.7ppm). 

This section contains carbon-13 NMR chemical shifts which are representative for this class of compounds. Although most of the chemical shifts available are of acid chlorides, the chemical shifts observed for several acid bromides indicate that the C(=0)-Br group has a more strongly deshielding effect on adjacent aliphatic groups than does the C(=0)-Cl group. 

This section concerns itself with the carbon-13 NMR chemical shifts of compounds containing the primary amide group (- C(=0)-NH2). 

Table 4 Proton and carbon-13 NMR chemical shifts (5 ppm) for ring H and C for (2).

Table 8 Carbon-13 NMR chemical shifts (ppm) for benzo[c]furan derivatives.

Carbon-13 NMR chemical shifts for a variety of aurones (139) are reported and discussed in order to determine how the substituent effects can be used for structural elucidation <83H2203>. Substituent effects seem not to influence the C chemical shifts of furan-2,3-dione derivatives (140) and (141) <91BSF393>. The modification of the substituent in the para position of the phenyl ring (140) or the strain induced by the bridge (141) do not greatly affect the chemical shifts of the carbon atoms of the furandione ring. 

Carbon-13 NMR chemical shifts, Ju-c and Jc-h coupling constants have been determined for methyllithium in THF, diethylether, and triethylamine solutions (164). These data are reported in Table I. 

Levy, G. C., Lichter, R. L., and Nelson, G. L., Carbon-13 Nuclear Magnetic Resonance Spectroscopy, 2nd Edition, Wiley, New York, 1980. Pihlaja, K., and Kleinpeter, E., Carbon-13 NMR Chemical Shifts in Structural and Stereochemical Analysis, WCH, New York, 1994. 

Figure 13 NMR chemical shifts of a few selected xenon compounds. Adapted with permission from Jameson C (1987) The...

Section 13 19 2D NMR techniques are enhancements that are sometimes useful m gam mg additional structural information A H H COSY spectrum reveals which protons are spin coupled to other protons which helps m deter mining connectivity A HETCOR spectrum shows the C—H connections by correlating C and H chemical shifts... 

When dealing with polymeric materials these early techniques were limited by the fact that only protons could be readily observed in the available fields. The small chemical shifts and the large dipole interactions made work with these systems very difficult. However, the development of the routine Fourier transform method of observation, especially when observing C-13 NMR, significantly changed the situation. 

NMR chemical shift data from die protons ortho or para to the electron-withdrawing group can be used to determine the reactivity of the monomer indirecdy.58 Carbon-13 and 19F NMR can be used to probe the chemical shift at the actual site of nucleophilic reaction. In general, lower chemical shifts correlate widi lower monomer reactivity. Carter reported that a compound might be appropriate for nucleophilic displacement if the 13 C chemical shift of an activated Buoride ranges from 164.5 to 166.2 ppm in CDC1359. 

TABLE 7.4 Peak Assignments for 13 C NMR Chemical Shifts of Phenolic Resins"... 

The H-NMR and C-NMR chemical shifts have been assigned and substractures have been deduced on the basis of COSY-45° (Problem 5.13) and other spectroscopic observations. Interpret the HMBC spectrum and identify the heteronuclear long-range coupling interactions between the H and C nuclei. 

The HMQC spectrum of podophyllotoxin shows heteronuclear crosspeaks for all 13 protonated carbons. Each cross-peak represents a one-bond correlation between the C nucleus and the attached proton. It also allows us to identify the pairs of geminally coupled protons, since both protons display cross-peaks with the same carbon. For instance, peaks A and B represent the one-bond correlations between protons at 8 4.10 and 4.50 with the carbon at 8 71.0 and thus represent a methylene group (C-15). Cross-peak D is due to the heteronuclear correlation between the C-4 proton at 8 4.70 and the carbon at 8 72.0, assignable to the oxygen-bearing benzylic C-4. Heteronuclear shift correlations between the aromatic protons and carbons are easily distinguishable as cross-peaks J-L, while I represents C/H interactions between the methylenedioxy protons (8 5.90) and the carbon at 8 101.5. The C-NMR and H-NMR chemical shift assignments based on the HMQC cross-peaks are summarized on the structure. 

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