19F multiple region selected 2D NMR correlation experiments

The fundamental problem with observation of 19F in many 2D NMR sequences is that the bandwidth over which signals occur (approximately 100 kHz at 376 MHz) greatly exceeds the 90° excitation bandwidth of most liquids probes. Here we report a method that permits the acquisition of 2D 19F–13C HMQC experiments on compounds that have 19F signals separated by many times the actual 90° excitation bandwidth of the probe. The normal observe hard 90° and 180° pulses are replaced with region selected shaped pulses. The shaped pulses are convoluted to include excitation of a narrow region around each 19F signal while leaving the large signal-less regions unexcited. This method produces accurate 90° and 180° pulses on widely separated resonances.