Origin and remedy for HSQC artifacts in proton-detected INADEQUATE spectra.

NMR pulse sequences visualizing and bond connectivity an intermediate state of C-C double-quantum coherence and H detection are an indispensable tool to solve small-molecule structures at the natural abundance level of C. A longstanding issue with these experiments set up to display 2D spectra with single-quantum frequencies is that in addition to the H-C-C correlations of interest, appearance of HSQC-type artifacts can complicate analysis and obscure connectivities. The origin of these artifacts is described and remedies for their suppression are introduced. They include refocusing of couplings prior to creation of C-C double-quantum coherence, which is known to enhance sensitivity by reducing loss into zero-quantum coherence for pairs of two protonated C.