Single-frequency off-resonance

In the study of 13C-NMR spectra of 8 and 6, the presence of the hydroxyl group at C-14 is also evident since a downfield shift of 43 ppm from 6 (<521.2) to 8 (<563.87) is observed. The previously ambiguous assignments of C-15, C-16, C-5, and C-20 are also clarified through irradiation of H-16, H-5, and H-20 with low-power single-frequency off-resonance decoupling (SFORD) experiments. 

Singh et al [54] used a 13C NMR spectrometric method and reported the chemical shifts of primaquine and chloroquine. The signals are assigned on the basis of substituent effects on benzene shifts, intensities, multiplicities in single-frequency off-resonance decoupled and the comparison with structurally related compounds. 

Proton-noise decoupled and single-frequency off-resonance decoupled carbon-13 NMR spectra were determined for the CTC Working Standard (Figure 13). 

Graphical analyses of series of single-frequency off-resonance decoupled spectra,... 

Comparison with the complete 13C NMR signal assignments of steroids enabled the interpretation of the 13C NMR spectra of structurally related cardenolides and sapogenins [596, 597]. Besides single-frequency off-resonance decoupling and low power noise decoupling, spectra of specifically deuterated compounds were used as additional aids for the signal identifications. The 13C chemical shifts are collected in Table 5.12 and the... 

The signals of a large number of coumarin derivatives [418] were assigned using the single-frequency off-resonance decoupling,. /-modulated spin echoe and INEPT techniques. 

In single-frequency off-resonance decoupled (SFORD) spectra the magnitude of the coupling interaction between 13C and H is reduced so that normally only one bond C-H coupling patterns are observed and an A X situation is assumed. In such a decoupling the residual coupling JK is less than /(C-H) and depends upon the decoupling power (yB2) and the decoupler offset (Av). For most applications to structural work... 

An early report (2) on steroid 13C NMR includes discussion of the carbon chemical shifts of model compounds, single-frequency off-resonance decoupling, induced shifts upon acetylation, and deuterium exchange. These techniques are all amply reviewed by Blunt and Stothers (1) and are not specifically treated here. A particularly readable account of the off-resonance decoupling experiment is given in the text by Wehrli and Wirthlin. (3)... 

Noise and single frequency off-resonance decoupled CMR spectra of disopyramide phosphate in deuterated water solution are shown in Figures 4 and 5.2 Shifts are reported in ppm downfield from the shift of tetramethyl silane as referenced to a shift of 67.4 ppm for dioxane which was used as an internal reference. 

Single Frequency Off-Resonance Proton Decoupled Carbon Magnetic Resonance Spectrum of Disopyramide Phosphate... 

Nuclear Magnetic Double Resonance Nuclear Magnetic Resonance Nuclear Overhauser Effect Proton Noise Decoupling Rhamnopyranose Selective Frequency Decoupling Single Frequency Off-Resonance Decoupling... 

Figure 8.29 Single-frequency off-resonance decoupled (SFORD) NMR spectrum of 5-(l-acetoxy-l-methylethyl)-2-methyl-2-cyclohexenone in CDCI3.

Peak assignments were made for the spectra in Figure 1 on the basis of model compounds (Table II), substituent effects, single-frequency off-resonance decoupling, and peak intensities. The relatively large a- and p-substitutent effects for chlorine produce NMR spectra of chlorinated polymers that can span the... 

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