Figure 43.

RF schemes employed for the detection of heteronuclear proximities. Panel (a) shows long-range cross-polarization, e.g., between remote ¹H and ¹³C′ spins. Panel (b) shows the basic element of REDOR, TEDOR, and TREDOR used for nitrogen–carbon and proton–carbon recoupling. This element is shown on a single channel, preferably the one of the rare (least abundant) nucleus, i.e., ¹⁵N, to avoid recoupling of homonuclear interactions. Additional pulses can be incorporated on the other channel to compensate for RF pulse imperfections.