Decoupling experiments

NOE Nuclear Overhauser effect, change of signal intensities (integrals) dining decoupling experiments decreasing with spatial distance of nuclei... 

All P.M.R. spectra were measured with a Varian HA 100 spectrometer operating in the frequency-sweep mode with tetramethylsilane as the reference for the internal lock. The double and triple resonance experiments were performed using a Hewlett Packard 200 CD audio-oscillator and a modified Hewlett Packard 200 AB audio-oscillator (vide infra). Spectra were measured using whichever sweep width was required to ensure adequate resolution of the multiplets under investigation, generally 250 or 100 Hz, and sweep rates were selected as necessary. Extensive use was made of the Difference 1 and Difference 2 calibration modes of the instrument, both for the decoupling experiments and for the calibration of normal spectra. 

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. 

Composite pulses have also been used in overcoming problems due to sample overheating during broadband decoupling experiments. A widely used pulse sequence is Waltz-16 (Shaka et al., 1983), which may be repre-... 

Before the advent of 2D NMR spectroscopy, the classical procedure for determining proton-proton connectivities was by homonuclear proton spin decoupling experiments. Such experiments can still serve to determine some H/ H connectivities in simple molecules. 

One-dimensional double-resonance or homonuclear spin-spin decoupling experiments can be used to furnish information about the spin network. However, we have to irradiate each proton signal sequentially and to record a larger number of ID H-NMR spectra if we wish to determine all the coupling interactions. Selective irradiation (saturation) of an individual proton signal is often difficult if there are protons with close chemical shifts. Such information, however, is readily obtainable through a single COSY experiment. 

The determination of these two coupling constants can be carried out using a selective proton decoupling experiment. The middle trace in Fig. 18 shows the results of such an experiment. 

Of course, you can find yourself looking at spectra that are complex enough to warrant numerous decoupling experiments for elucidation. In these circumstances, running a single correlated spectroscopy (COSY) 2-D experiment as an alternative might well be the answer. A full explanation of the theoretical... 

R.3 in (3.1) is the transpose of the third column of R, and represents a unit vector directed along the static field B0. More generally R j, i = 1,2,3, denotes the ith column of R. This notation proved to be convenient in the description of ENDOR spectra, especially in more complex cases, e.g. in CP ENDOR, PM-ENDOR, DOUBLE ENDOR as well as in spin decoupling experiments (Sect. 4). 

Fig. 7.8 a Schematics for the FIDS experiment as explained in the text. A coupled and a decoupled experiment are recorded. The decoupled experi-... 

Assignments determined by H CHETCOR, H HCOSY, H- H decoupling experiments. cDetermine by DEPT sequence. 

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