Single frequency decoupling

Single-frequency decoupling is easy and rapidly carried out. However, it may be limited by the closeness of different multiplets. Also, it will not nonnally be possible to apply more than one frequency of decoupling irradiation at a time. Fortunately, these disadvantages do not apply to the equivalent multidimensional methods. 

Proton-noise or single frequency decoupled l3C FTnmr spectra obtained on a Varian XL-100-15D spectrometer at 25-1 MHz in D2O on 0 1 M compound. Chemical shifts corrected to TMS scale using 6CH3C02H 178 3 ppm. 

The structure of arenaine (84) was revealed from the interpretation of its n.m.r. ( H and C) spectra. Examination of the C noise resonance decoupled and single frequency decoupled spectra showed the presence of three non-proto-nated carbons (carbonyl, guanidine, and a-amino-tetrahedral types), three methine (olefinic methine, aminomethine, and one other) carbons, three methylenes (one olefinic and two saturated ones which appear at highly shielded and deshielded positions, thus implying that they are part of a R3CCH2CH2 unit), and two methyl groups. This information alone allows formulation of the... 

Homonuclear single-frequency decoupling can also be used to simplify the multiplicities of other resonances. Flomonudear decoupling, however, can potentially overload the receiver, because irradiation may... 

Figure 3.16. Proton noise decoupling techniques (a) single-frequency decoupling (b) noise decoupling. Irradiation of He in (a) results in the collapse of only one carbon, Cc, to a singlet. Proton noise decoupling (b) results in all the carbon atoms appearing as singlets.

The assignments of NMR signals for cytochalasin D (6) were made by single-frequency decoupling and PRFT, as for cytochalasin B (26) (Graf et al, 1974). 

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,... 

Using single-frequency and noise-modulated resonance and off-resonance proton decoupling, 7] relaxation time measurements, relaxation reagents like Gd (fod)3 and specifically deuterated compounds, all the carbons in retinal isomers, the model compounds a-and /i-ionone, and vitamin A and its isomers [165, 555-557] were assigned. The olefinic ring carbons (C-5 and C-6) could be identified on the assumption that the 13C relaxation times are dominated by intramolecular dipole-dipole interactions with neighboring protons and that the same rotational correlation time characterizes the interactions for both carbons. Consequently the ratio of T/s for C-5 and C-6 can be estimated from eq. (5.1)... 

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... 

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