Carbon frequency

Calculated versus Observed Carbon—Carbon Frequencies... 

The magnetization has now been successfully transferred from the HN spin to the intraresidual and sequential 13C spins or alternatively to the interresidue 13C spin either using HNCA-TROSY or HNCO-TROSY schemes, respectively. It is inevitable that the HNCO-TROSY spectrum cannot be used for the sequential assignment alone because it does not bridge two sequential N shifts through common carbonyl carbon frequency. The... 

The first liquid-state application, reported by Fisher et al. [18], used two coils, both tuned to the carbon frequency of 75.44 MHz at 7.4 T. The coils were... 

Figure 4. Symmetric and asymmetric adsorbed carbonate frequencies versus a uniform external electric field applied perpendicularly to the surface.

Chapter 1, sections 1-2 Transition metal hydrides, pp. 1-8, tables 1.1-1.10. Chapter 3, sections 1-8 Metal-carbon frequencies in carbonyls and cyanides, pp. 84-111, 118-119, tables 3.1-3.20,... 

Figure 10 Portions of NOESY spectra and 1D slices through the frequencies of aromatic protons, (a) A 150-ms 2D NOESY spectrum of a 27-nt DNA stem-loop 93 a slice through the frequency of A5H8 is shown, (b) A 200-ms 2D NOESY spectrum of a 34-nt RNA stem-loop 68 a slice through the frequency of C7H6 is shown. Assignments of H5 and H5" protons are tentative. Note that some of the cross-peaks partially overlap with cross-peaks in another slice through the frequency of A8H2. (c) A 150-ms 3D 13C-edited NOESY-HMQC spectrum of the same molecule shown in (b). A slice of the proton and carbon frequencies of H6 and C6 in residue C7 are shown. Note a significantly lower digital resolution in the indirect uj2 dimension in this spectrum compared to the indirect u1 dimension in the 2D NOESY spectrum shown in (b).

In general the next group of carbon frequencies is those associated with heteroatoms, e.g., C-21 in Aspidosperma alkaloids, where the heteroatom is oxygen, or C-20 in pandoline (220), where the atom is oxygen. As expected, attachment to both oxygen and an electron-withdrawing group has a substantial effect, e.g., C-16 in vindoline. 

Heteronucleus-detected shift correlation experiments have now been largely supplanted by far more sensitive proton- or inverse -detected methods. The heteronu-cleus-detected experiments are now largely reserved, in laboratories with modem NMR spectrometers, for those occasions when very high digital resolution is needed in the carbon frequency domain because of high spectral congestion [109, 110]. The remainder of this section will focus on the now widely utihzed proton-detected heteronuclear shift correlation methods. 

Figure 4.5 Proton-decoupled CnTi values of a natural rubber, observed at carbon frequencies of 45.2 MHz (central set) and 22.6 MHz (lower set) plus NOE values at 45.2 MHz (upper curves). The labelling is f CH2(A)-C(Me)=CH( )-CH2( ) and the solid curves are calculated from the 3-t theory described in the text.

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