Exchange spectra

Figure 5.47 Two-dimensional exchange spectrum of N,Af-dimethylacetamide and its generation, (a) The first set of spectra results from the first series of Fourier transformations with respect to The modulation of signals as a function of t is observed, (b) The second set of spectra is obtained by the second series of Fourier transformations. The unmodulated signals appear on the diagonal at (v, v ), (vx, Vx), and (v, v ), whereas the modulations due to exchange show up as crosspeaks on either side of the diagonal at (vx, Vx) and (vx, Vx). (c) A contour plot representation of (b). (Reprinted from Science 232, A. Bax, et ai, 960, copyright (1986), with permission from Science-AAAS, c/o Direct Partners Int., P.O. Box 599, 1200 AN Hilversum, The Netherlands)...

The principle of detailed balance (and the micro reversibility) [48] requires that 2D exchange spectrum A Tm) is always symmetric. The matrix A(0) represents a 2D exchange spectrum recorded at = 0. It is a diagonal... 

Fig. 42 Contour plot of a 2D exchange spectrum of phenyl deuterated BPA-PC at - 40 °C, with tm = 500 ms (from [38])...

Figure 12.8 Two-dimensional 129Xe NMR exchange spectrum of the blend of Figure 12.7 with an exchange time of 5 seconds. The clear cross-peaks between the peaks due to absorbed Xe shows that within the exchange time the Xe atoms change location very often. During 5 seconds no exchange with the gas surrounding the...

In Section 12.3 it was described how, with the help of a two-dimensional exchange spectrum, domain sizes in the iPP/EP blend are estimated. There an estimated value for the Xe diffusion coefficient was used. Now with experimental data from Table 12.2 the average EPDM domain size for the iPP/EPDM blend can be calculated. It was assumed that the structure of the EPDM in the blend is the same as in the pure material, (i.e., the Xe diffusion coefficient in the EPDM domains in the blend is equal to the measured D for pure EPDM and likewise for iPP), then for Xe in the EPDM domain during A = 1.2 seconds is 20 grn. In the same time for Xe in the iPP matrix is approximately 5 grn. These distances for a diffusion time of 1.3 milliseconds, the inverse of the frequency difference 770 Hz of the two lines in the Xe NMR spectrum of the blend, are 0.6 and 0.2 grn, respectively. The average size of the EPDM domains in the iPP/EPDM blend is... 

Fig. 23. The form of the reduced three-dimensional DICO experiment.52 The experiment produces a two-dimensional experiment that is in effect, the projection of the full three-dimensional exchange spectrum onto the diagonal plane shown. This spectrum is then sufficient to determine whether two different motional processes revealed by the experiment are correlated.

PPh2 (CO)12]fc (n = 1 or 2) [Cu2Ru6C(CO)a6(NCMe)2] bipyramid Ru octahedron 2 spectra suggest Cu atom site exchange spectrum shows No 33... 

This two-dimensional 13C exchange spectrum is of the methyl region of the heptamethylbenzene cation in concentrated sulfuric acid solution under conditions where methyl group migration is occurring. Is the migration process 1,2 or 1,3 or 1,4 or random ... 

The reaction of osmium atoms with benzene in the vapour phase produces the yellow compound [OsC H J. The signals appearing in its 1H spectrum are listed below, and the lH 1H exchange spectrum of the compound is shown on the right. What exchange process is occurring ... 

Fig. 45. H 2D-NOESY and exchange spectrum of 74c (toluene-

Figure 13.20. Contour plot of the 2D l3C exchange spectrum of compound 10-18. (Contributed by Alan Sopchik of Wes Bentrude s group at the University of Utah.)...

The relevant part of the 2D 13C exchange spectrum of this molecule (at -90°C in toluene-d8) is shown in the contour plot of Figure 13.20. Note how the symmetrically placed cross peaks indicate that the signals at 5 52.1 and 56.15 are correlated by exchange at -90°C, even though this exchange is not apparent in the ID spectrum until the temperature is raised much higher. 

Texch- The relation between this A and the 2D exchange spectrum S is given by... 

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