Isolation of selected exchange processes in nuclear magnetic resonance

It is possible to inhibit the transfer of magnetization in a system with several exchanging sites in dynamic equil., as in a mixt. of cis- and trans-ZrCl4L2 with excess free ligand L (L = (CH3O)3PO). The forward and backward reaction rates involving two selected sites can be studied while the effect of competing exchange processes is quenched. This can be achieved either by selective inversion of the magnetization of the two chosen sites in the reaction interval, or alternatively by inversion of the magnetization of all other sites in the exchange network. The rate of exchange from the free to the cis site is kcic->free = 0.018s-2. In the usual methods, this process would tend to be overshadowed by the almost two hundred times faster competing exchange process from the cis to the trans site (ktrans->cis = 3.32 s-1). [on SciFinder (R)]