Dipolar interaction between proton and

Mastui et al.29S proposed a new version of the magic echo (ME) sequence, called tetrahedral magic echo (TME), which uses the so-called tetrahedral angle 0=109.5° instead of 90° in the ME or modified ME (MME). This is substantially superior to ME or MME line narrowing for solids where heteronuclear dipolar interaction between protons and the other nuclear species is comparable to the homonuclear proton-proton interaction. 

It is recognized that the signal of all benzyl protons is clearly removed in deutrated samples of the benzyl group [Glu(OBzl)]n-(/7, but the signal-to-noise (S/N) ratio and the resolution are not sufficient, as shown in Fig. 30(C). In spite of adopting a very long recycle delay time of 200 s in NMR measurements (the routine recycle delay is 10 s), measurement of the appropriate spectrum of a [Glu(OBzl)]n-r/7 sample is not successful. The most likely reason for this may be a heteronuclear dipolar dipolar interaction between proton and deuterium. For instance, if it is assumed that the distance between a proton and deuterium in... 

CP is mediated by the heteronuclear dipolar interaction between proton and the target spin. Since the direct dipolar interaction strongly depends on... 

For a rigidly held, three-spin system, or when existing internal motion is very slow compared to the overall molecular tumbling, all relaxation methods appear to be adequate for structure determination, provided that the following assumptions are valid (a) relaxation occurs mainly through intramolecular, dipolar interactions between protons (b) the motion is isotropic and (c) differences in the relaxation rates between lines of a multiplet are negligibly small, that is, spins are weakly coupled. This simple case is demonstrated in Table V, which gives the calculated interproton distances for the bicycloheptanol derivative (52) of which H-1, -2, and -3 represent a typical example of a weakly coupled, isolated three-spin... 

On the other hand, LD/MAS spectra of the nylon 4 single crystal sample shown in Fig. 12.2(c), show an obvious change from 20 to 100°C. In the spectrum at 20°C, no peak is observed owing to the broadening caused by dipolar interactions between carbons and protons. Such broadening at 20°C cannot be overcome by the low power decoupling for protons used in... 

Figure 5.3 (a) Dipolar interaction between a and proton spin. The fi are the z components of the magnetic moments, and is the z component of the proton dipolar field at the nucleus, (b) Dipolar splitting of isolated CH pairs at one angle relative to the magnetic field. 

The NOESY spectrum of 7-hydroxyfrullanolide reveals the spatial proximities between the various protons. Cross-peak D arises from the gemi-nal coupling between the exomethylenic geminal protons (8 5.71 and 6.06). Dipolar interaction between the 06 proton (8 4.97) and the allylic methyl protons (8 1.64) is inferred from cross-peak C. This interaction is possible only when the C-6 proton is a-oriented. The C-1/3 and 02/8 protons (8 1.31 and 1.45, respectively) exhibit cross-peaks... 

The terms pc and py correspond to 1/Tic and 1/Tih, respectively, and CTCH is the cross-relaxation rate. It should be stressed that the simplicity of the above equation is a consequence of the rareness of the I spins and of the dominant strength of the dipolar interaction between directly bonded nuclei. The situation for homonuclear proton spin systems is often more complicated, since the protons usually constitute a much larger spin system, and a separation into distinct two-spin systems may be not valid in this case. The broadband irradiation of the protons yields, in a steady state, Mhz = 0 and M z = Mj (1 rj). The factor 1 + 77 is called, as introduced above, the nuclear Overhauser enhancement factor. The NOE factor is related in a simple way to the equilibrium magnetizations of the I- and S-spins (which are proportional to the magnetogyric ratios 71 and 7s), the cross-relaxation rate and the relaxation rate of the I-spin ... 

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