The Multiplicity-Edited HSQC Experiment

The following parametersc re appropriate for edited HSQC experiments  

In Section 7-9a, we saw that the critical delay time A in the HMBC experiment is set to approximately 8 Hz, which is an average value of (2 7ch) with n usually equal to 2 or 3. Implicit in this relationship is the fact that the HMBC experiment cannot differentiate two-bond from three-bond (and occasionally greater) X-H couplings. This is an unfortunate shortcoming, especially with regard to problems involving structural elucidation (Chapter 8). 

Several features can be observed in the two spectra shown. First, the tilting of two-bond cross peaks appearing at the coordinates 8 26.0/S2.17 (C3, H2 ) and 8 26.0/80.96 and 

In addition to discriminating between two- and three-bond X-H couplings, the 7, 7-HMBC experiment makes use of what is known as accordion excitation. In this technique, critical vector dephasing and refocusing times are varied so that the experiment is optimized for a range of two- and three-bond X-H couplings and not for just an average 7xh  

pseudo-echo, sine bell, or squared sine bell weighting (all of which can be left shifted to improve sensitivity) 

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