multiple region selective HMQC

In 2D NMR measurements involving ¹⁹F, unlike those for ¹H and ¹³C only, wide  chemical shifts of ¹⁹F make it difficult to detect correlation peaks. RF pulses should  manipulate magnetizations as designed, and otherwise signal intensities become  considerably low. In multiple region selective (mrs) HMQC,^{1) 19}F pulses are  replaced by a selective excitation E-BURP1 pulse and a selective refocusing RE-  BURP pulse, and several frequency regions are simultaneously excited/refocused  using shifted laminar pulses, permitting all the correlation peaks to be detected.

Fig. 1  Pulse diagram of mrs-HMQC

Fig. 2  mrs-HMQC spectra of CF₃CHFCF₂OCH₂CH₃
Spectrometer: JNM-ECA500
 

Conventional HMQC method, where the offset of ¹⁹F rectangular pulses is fixed at -80ppm, does not give a correlation peak at -210ppm, but all the correlation peaks  are detected in the mrs-HMQC spectrum.

Reference

1) S. Cheatham and J. Groce, J. Fluorine Chem. 125, 1111(2004).