BIRD Pulse and X-Filters

Many NMR studies of nuclides of low sensitivity (nucleus X) that are spin coupled to protons are now carried out by indirect detection of the proton resonance, primarily by multidimensional NMR methods that we discuss later. For such detection to be effective for an X that is in low natural abundance (such as 13C) or is selectively enriched, it is essential to discriminate against the much larger signal arising from proton resonances of molecules with a nonmagnetic form of the nuclide (e.g., t2C).We describe here two simple ways to achieve such discrimination. 

FIGURE 9.8 (a) Bilinear rotation decoupling (BIRD) pulse sequence, (b) Behavior of the H magnetization from a proton coupled to 13C. (c) Behavior of the H magnetization from a proton not coupled to 13C. See text for details. 

Other pulse sequences, known collectively as X-Jilters, are also used to discriminate in favor of or against resonances from H coupled to X. For example, in 

---