Selective Spin Decoupling. Double Resonance

Intense irradiation of a proton (or equivalent protons) at its resonance frequency in a spin-coupled system removes the proton s coupling effect on the neighboring protons to which it has been coupled. Thus successive irradiation of the protons of 1-propanol, for example, yields the following results  

we have a powerful tool for determining the connectivity of protons through bonds and assigning proton peaks. Furthermore, overlapping peaks can be simplified by removing one of the couplings. 

In spectrum (b), the H-l protons are irradiated, and the H-2 triplet of doublets is collapsed to a doublet (/ = 3). This doublet results from long-range coupling with H-4. In spectrum (c) the H-2 triplet of doublets is irradiated, and the H-l triplet is collapsed to a singlet, and the H-4 is collapsed to a singlet. 

The overall information obtained from selective spin decoupling is connectivity —that is, progressing through the protons of the carbon chain. 

It is also possible to simplify two overlapping multiplets by selectively irradiating a neighboring proton, thus disclosing multiplicity and coupling constants in the residual multiplet. 

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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. 

A wide variety of ID and wD NMR techniques are available. In many applications of ID NMR spectroscopy, the modification of the spin Hamiltonian plays an essential role. Standard techniques are double resonance for spin decoupling, multipulse techniques, pulsed-field gradients, selective pulsing, sample spinning, etc. Manipulation of the Hamiltonian requires an external perturbation of the system, which may either be time-independent or time-dependent. Time-independent... 

Most other homonuclear double-resonance techniques, with names such as spin tickling and selective decoupling, provide information about the arrangement of spin states and the... 

Selective decoupling spin-spin interactions by the double resonance technique. The sample is simultaneously irradiated with two radio-frequency fields one frequency gives the resonance pattern of interest, and the other frequency is the resonance frequency of the coupled nuclei. When the second proton is irradiated with sufficient intensity, the spin-spin coupling collapses giving simple spectra. 

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