Decoupling of resonance

In the absence of decoupling, the resonances would each be split by at least four short- and long-range... 

The possible presence in the 4-chloro-4-hexenyl trifluoroacetate of small amounts of two cis-trans pairs of products of addition of trifluoroacetic to the triple bond without concomitant halogen shift remains speculative. In any event these compounds would be removed as ketones upon hydrolysis of the trifluoroacetate. Both the 4-chloro-4-hexenyl trifluoroacetate and the alcohol resulting from its hydrolysis have been shown to contain 9% of the (E) isomer. In the present study the hydrogen decoupled magnetic resonance spectra of the ester and alcohol were shown to contain peaks attributable to approximately 9% of E) isomer. 

It should be noted that it would have been totally impossible to have effected these decoupling experiments by the field-sweep method a>i has to be scanned ca. 100 Hz to observe the H2 resonances which of course would require < >2 to be scanned by an equal amount. Since it is not possible to obtain a decoupling field of this magnitude, the above experiment would merely result in partial decoupling of the H2 resonances. 

Most 13C spectra are run on Fourier-transform NMR (FT-NMR) spectrometers using broadband decoupling of proton spins so that each chemically distinct carbon shows a single unsplit resonance line. As with NMR, the chemical shift of each 13C signal provides information about a carbon s chemical environment in the sample. In addition, the number of protons attached to each carbon can be determined using the DEPT-NMR technique. 

The intensity of resonances may be increased by up to 200% when iR nuclei which are directly bonded to the carbon atom are irradiated. This effect is very important in increasing the intensity of spectra when they are proton-decoupled. The efficiency of the proton/carbon NOE varies from carbon to carbon and this is a factor that contributes to the generally non-quantitative nature of NMR. While the intensity of protonated carbon atoms can be increased significantly by NOE, non-protonated carbons (quaternary carbon atoms) receive little NOE and are usually the weakest signals in a NMR spectmm. 

The structure of the two rhodium-acyl complexes was elucidated using COSY90 spectra, selective decoupling of the phosphorus resonances, and HMQC spectra. Spectrum 3d (Figure 6.13) shows the complete simulation of the NMR spectrum obtained at 223 K. The NMR spectrum... 

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