Double resonance, homonuclear

The double resonance experiment can be used to simplify a spectrum as discussed above, or to probe correlations between different nuclei. Two types of double resonance experiments are described. In the homonuclear double resonance experiment the nuclei irradiated are the same isotope as those observed Shorthand... 

When the two sets of nuclei are of different isotopes (e.g.,, 3C and H), the experiment is described as heteronudear double resonance. When we observe the signal from nuclei of isotope A while irradiating nuclei of isotope B, we label the resulting spectrum with the shorthand designation A B. When the two sets of nuclei belong to the same isotope (e.g., both 1H), the technique is described as homonuclear double resonance. 

These two examples show that Av is very much smaller for homonuclear double resonance, suggesting a simple way to generate v2. Instead of using a separate rf oscillator, we can use part of the output from the v, channel electronically modulated with an audio-frequency signal to generate output at v2. This technique makes it easier to control the exact value of Av and to focus v, and v2 exactly where we want them. 

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... 

Homonuclear double resonance indicates that both V and v2 are focused on nuclei of the same isotope, while heteronuclear double resonance indicates that the V and v2 are focused on different isotopes or elements. 

In CIDNP studies the pattern of nuclear spin polarizations is used to deduce the structures of free radical intermediates, and if there is a simultaneous NOE this can affect the conclusions drawn. (344) In the photolysis of [10] to yield [12] the biradical intermediate [11] should not cause significant polarization of the olefinic protons of [10] but in fact these are observed to have weak emission. This raises the possibility that the intermediate is really the biradical [13], but a homonuclear double resonance experiment which destroyed the cyclopropyl spin polarization of [10] eliminated the olefinic emission which was evidently solely due to the NOE. Thus it is confirmed that [11] is indeed the intermediate in the reaction. (344)... 

Experiments in which both the irradiated and the observed nuclei are protons are called homonuclear double-resonance experiments and are represented by the notation The irradiated nucleus is denoted by braces. When the observed and irradiated nuclei are different nuclides, as in proton-decoupled spectra, the experiment is a heteronuclear double-resonance experiment and is denoted, for example, C H. ... 

One of the first steps in a conventional assault on a complex assignment problem in proton NMR is to run a series of homonuclear double resonance experiments. Not only can this establish which multiplets have a mutual J coupling, but it can reveal hidden resonances obscured by overlap, through their couplings to less crowded parts of the spectrum. Since a separate experiment is needed for each multiplet, this approach can be quite time-consuming. Similar information can however be obtained more efficiently by 2D NMR methods indeed, this was the purpose of the first 2D NMR experiment, proposed by Jeener in 1971. 

As Figure 10 shows, the pulse sequence of Figure 11 with the phase cycling scheme [13] can give 2D spectra that are quite clean and easy to interpret. The spectrum of Figure 10, for an aqueous solution of the cyclic peptide antibiotic viomycin, summarizes all the coupling and connectivity information that would be obtained from a complete series of homonuclear double resonance experiments. A similar spectrum is discussed in more detail in reference 52. 

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