Anti-phase doublets

Figure 14 Determination of interglycosidic coupling constants of Me-/ -D-lactoside, shown in the inset, using F1 traces from IPAP DEPT-INADEQUATE spectra. The long-dashed lines are the sum or the difference of the in-phase (solid line) and anti-phase doublets (short-dashed line).

Fig. 5-11 also shows the CIDEP spectra calculated with this model (a) 7 > 0 J (w > 0 J) and (b) 7 < 0 J (w < 0 J). As clearly seen in this figure, each spectrum has two anti-phase doublets with an A/E (E/A) pattern for 7 > 0 J (7 < 0 J). Similarly, one can show that it has an E/A (A/E) one for a radical pair generated from an S-precursor for 7 > 0 J (7 < 0 J). The splitting of each anti-phase doublet corresponds to 27. This is a novel method to determine the 7 values of radical pairs and biradicals in solution. Let us consider the conditions for detecting the CIDEP of spin correlated radical pairs. When 3 (= 7/ ) is much larger than Q, little polarization can be obtained because Ipg becomes very small from Eq. (5-43). When 3 (= 7 ti ) is smaller than the line width of each ESR line, the CIDEP signals also vanishes because the anti-phase components of each doublet cancel out with each other. For intermediate 3 (= 7/ft ), CIDEP due to the SCM becomes intense. Each of the anti-phase... 

Figore 5.79. The ID INADEQUATE e ieiiment (b) selects for the carbon-13 satellites in the conventional carbon-13 plectrum (a) and provides a means of measuring carbon-carbon coupling constants (here marked as anti-phase doublets). Some residual parent resonances from lone centres remain in (b). 

On the other hand, if the correlated radical pair mechanism is operative, a pair of partially overlapping anti-phase doublets is expected.[36-38] The polarization pattern observed, E A E, is similar to that observed for P700 - A in Photosystem I of green plants, [24] and P865 -Q in bacterial reaction centers. [25] Recently, Stehlik et al. [39] have developed a simple theoretical model that can be used to simulate these spectra. This model focuses on the influence of/, D, and g-anisotropy on the EPR spectra of radical pairs. The latter two quantities are particularly useful in determining the distance between the radicals and their mutual orientation. The... 

Figure 10 Examples of the analysis of long-range cross peaks in (A) isotropic and (B) aligned sample of Me-/ -D-xylopyranoside. Short-dashed and solids lines show anti-phase (AP) and in-phase (IP) multiplets. Long-dashed singlets were obtained by the addition and subtraction of the IP and AP multiplets using appropriate scaling factors. (C) Overlay of two one-bond cross peaks from isotropic (solid line) and aligned (dashed line) samples. The multiplets were shifted to overlay on one line of the doublet in order to accentuate the difference between J and D.

Two peaks in Fv at Q] jzJ]2, are expected these are just the two lines of the spin 1 doublet. Note that the two peaks have opposite signs - that is they are anti-phase in Fv In addition, since these are cosine modulated we expect the absorption lineshape (see section 7.2). The form of the cross-peak multiplet can be predicted by "multiplying together" the Fl and F2 multiplets, just as was done for the diagonal-peak multiplet. The result is shown opposite. This characteristic pattern of positive and negative peaks that constitutes the crosspeak is know as an anti-phase square array. 

The calculation predicts that two two-dimensional multiplets appear in the spectrum. Both have the same structure in Fx, namely an in-phase doublet, split by (JX2 + J23) and centred at (Qx + 23) this is analogous to a normal multiplet. In F2 one two-dimensional multiplet is centred at the offset of spins 1, Qx, and one at the offset of spin 3, Q, both multiplets are anti-phase with respect to the coupling JX3. Finally, the overall amplitude, Bl3, depends on the delay A and all the couplings in the system. The schematic spectrum is shown opposite. Similar multiplet structures are seen for the double-quantum between spins 1 2 and spins 2 3. 

Recall also that following the second pulse, some magnetisation remains associated with the original spin . Thinking back to the discussions of polarisation transfer in the INEPT experiment, it was shown that the basic requirement for the transfer of polarisation was an anti-phase disposition of the doublet vectors of the source spin, which for INEPT was generated by a spin-echo sequence. Magnetisation components that were in-phase just before the second 90° pulse would not contribute to the transfer, hence the A period was optimised to maximise the anti-phase component. The same condition applies for... 

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