Double irradiation resonance

The nuclear Overhauser effect (NOE) is a consequence of the modulation of the dipole-dipole interactions (through space) between different nuclei and is correlated with the inverse sixth power of the internuclear distance. Experimentally, the NOE is the fractional change in intensity of one resonance when another resonance is irradiated in a double-irradiation experiment. The NOE phenomenon is intimately related to spin relaxation. The NOE varies as a function of the product of the Larmor frequency, co0, and the rotational correlation time, tc. In small molecules, tc is short relative to uo"1. In this extreme motional narrowing situation, the frequency... 

In addition, its proton magnetic resonance spectrum unambiguously supported the 5-ketose structure (69). Rearrangements of epoxides to ketones when dicobalt octacarbonyl is used as the catalyst at temperatures above 100 , or when cobalt hydrocarbonyl is used at lower temperatures, are well known. By applying the technique of double irradiation to a sample of (68), the main component was shown to possess structure (68). Presumably, the free aldehyde group of the hydroformylation product immediately cyclized with the free hydroxyl group on C-3 to give the tricyclic structure (68). A third component (68a) (isolated in less than 5 % yield) was undoubtedly formed by subsequent reduction of the dialdose derivative (68). 

Special effects may be routinely and elegantly created by using sources of radiofrequency energy in addition to the observation frequency (uj = yBi) y = y/2i ). The technique is called multiple irradiation or multiple resonance and requires the presence of a second transmitter coil in the sample probe to provide the new irradiating frequency ( 2 = yBi). When the second frequency is applied, the experiment, which is widely available on modern spectrometers, is termed double resonance or double irradiation. Less often, a third frequency (U3 = yBf) also is provided, to create a triple-resonance experiment. We already have seen several examples of multiple-irradiation experiments, including the removal of... 

Figure 5-12 The 400 MHz spectrum (in part) of progesterone (a) without double irradiation and (b) with irradiation of the CH3-19 resonance displayed as a difference spectrum. (Reproduced with permission from J. K. M. Sanders and B. K. Hunter, Modern NMR Spectroscopy, 2d ed., Oxford University Press, Oxford, UK, 1993, p. 191.)...

Figure 4.20. The NMR spectrum of H Hu-cyclohexane (QHiDn) at 60MHz as a function of temperature. Coupling between H and has been removed by double irradiation (redrawn from Bovey, F. H. Nuclear Magnetic Resonance Spectroscopy, Academic Press, New York, 1969, p. 191).

Indeed, a lot of N parameters have been obtained in the past through CW double resonance experiments. In this area, the various techniques of double irradiation can be exploited and information about... 

When freshly prepared shows two resonances (equal intensity) t = 2.74, 5.83, which in time become one resonance at t = Rh coupling observed only under proton-proton double irradiation. 

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 development of a wide range of special forms of EPR was initiated when the idea of double resonance (using simultaneous irradiation by two different sources) was cast in 1956 by G. Feher at Bell Telephone Labs in his seminal paper on ENDOR, electron nuclear double resonance (Feher 1956). BioEPR applications of ENDOR were later developed on flavoprotein radicals in a collaboration of A. Ehrenberg and L. E. G. Eriksson in Stockholm, Sweden, and J. S. Hyde at Varian in Palo Alto, California (Ehrenberg et al. 1968), and on metalloproteins in a joint effort of the groups of R. H. Sands in Ann Arbor, I. C. Gunsalus in Urbana, Illinois, and H. Beinert in Madison (Fritz et al. 1971). 

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