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

NMR pulse sequences visualizing 1 J CC and n J CC bond connectivity via an intermediate state of 13 C- 13 C double-quantum coherence and 1 H detection are an indispensable tool to solve small-molecule structures at the natural abundance level of 13 C. A longstanding issue with these experiments set up to display 2D spectra with single-quantum frequencies is that in addition to the 1 H- 13 C- 13 C correlations of interest, appearance of HSQC-type artifacts can complicate analysis and obscure J CC connectivities. The origin of these artifacts is described and remedies for their suppression are introduced. They include refocusing of 1 J CH couplings prior to creation of 13 C- 13 C double-quantum coherence, which is known to enhance sensitivity by reducing loss into zero-quantum coherence for pairs of two protonated 13 C.