Single frequency proton decoupling

Single-frequency proton decoupling, also known as selective decoupling, depends upon proper assignment and identification of the proton resonances for a given molecule. Once the proton resonances are identified in an NMR spectrum, it is possible to irradiate specific... 

In the last few years, the impact of the use of 13C n.m.r. spectroscopy in natural product chemistry has been substantial, and in this regard alkaloids have not escaped attention. The natural-abundance 13C n.m.r. spectrum of nicotine has been determined at 15.8 MHz using both the noise-modulated total proton decoupling and the specific and off-resonance, single-frequency proton decoupling... 

Tx relaxation studies can determine the number of protons within two bond distances of a quaternary carbon nucleus. Other spectroscopic techniques applied to establish more rigorously the cmr assignments include selective single-frequency proton decoupling and nuclear Overhauser enhancement experiments. Chemical methods such as selective deuteration, selective C-13 incorporation, and shift reagent experiments have also been applied in some of the studies reported here. 

The thoroughness of this study is reflected in the complete assignment of all 16 carbon resonances by off-resonance decoupling and single-frequency proton decoupling experiments and by the use of model compounds. The pH dependence of the chemical shift of the carboxy-group C-16 aided in its differentiation from the ft-lactam C-8 carbonyl group. ... 

The carbons of interest in DHA are C4, C5, and C6. Carbons-1, -2, and -3 appear as singlets. Carbons-4 and -5 appear as doublets, and C6 appears as a triplet. Because C4 and C5 both appear as doublets, assigning chemical shifts to these carbons without further information would be diflBcult. It was important, therefore, to perform a series of single-frequency proton-carbon decoupling experiments, while maintaining the oflF-resonance decoupling. 

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

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)... 

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... 

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. 

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