Two-dimensional chemical exchange

C, M. DiMeglio, K. J. Ahmed, L. A. Luck, E. E. Weltin, A. L. Rheingold, and C. H. Bushweller,/. Phys. Chem., 96, 8765 (1992). Stereodynamics of Sterically Crowded Metal-Phosphine Complexes fra s-[(r-Bu),P( -Pr)],MCl2 [M = Pt(II) and Pd(II)]. One-Dimensional Dynamic and Two-Dimensional Chemical Exchange NMR Studies. X-Ray Crystallographic Studies, Molecular Conformation Trapping, and Molecular Mechanics Calculations. 

Macura S, Huang Y, Suter D, Ernst RR (1981) Two-Dimensional Chemical Exchange and Cross-Relaxation Spectroscopy of Coupled Nuclear Spins. J Magn Reson 43 259... 

S. Macura, Y. Huang, D. Suter, R.R. Ernst, Two-dimensional chemical exchange and cross-relaxation spectroscopy of coupled nuclear spins, J. Magn. Reson. 43 (1981) 259-281. 

Two-dimensional homonuclear /-resolved and COSY Si spectra have been used to study polymeric species in aqueous potassium silicate solutions enriched in Si, and a two-dimensional chemical exchange Sn spectrum has been reported for a five-coordinate ditin compound. Much work has been done on Si NMR in the solid state using magic angle spinning (MASS) and cross-polarization (CP) methods, and this technique has potential also for Sn and Pb. 

It can be seen from the following discussion that this can lead to a three-dimensional spectrum in which two-dimensional anisotropic exchange spectra for the different chemical sites are separated according to the isotropic chemical shifts associated with the different sites. Consider first a two-dimensional VACSY experiment (Fig. 26), in which a simple FID is collected under sample spinning at different spinning angles. The signal acquired has the form... 

Since we are going to rather extensively use the Hamiltonian (4.40) in the sequel, as a simplest two-dimensional model for an exchange chemical reaction, it is beneficial to establish some of... 

Figure 3.1 The various time periods in a two-dimensional NMR experiment. Nuclei are allowed to approach a state of thermal equilibrium during the preparation period before the first pulse is applied. This pulse disturbs the equilibrium ptolariza-tion state established during the preparation period, and during the subsequent evolution period the nuclei may be subjected to the influence of other, neighboring spins. If the amplitudes of the nuclei are modulated by the chemical shifts of the nuclei to which they are coupled, 2D-shift-correlated spectra are obtained. On the other hand, if their amplitudes are modulated by the coupling frequencies, then 2D /-resolved spectra result. The evolution period may be followed by a mixing period A, as in Nuclear Overhauser Enhancement Spectroscopy (NOESY) or 2D exchange spectra. The mixing period is followed by the second evolution (detection) period) ij.

---