Rolf Minkwitz tried to correlate small peaks in the proton dimension with their carbon frequencies. Two experiments, Heteronuclear Multiple Quantum Coherence (HMQC) and HETCOR (C,H Correlation by Polarization Transfer), provide that information.

Rolf tried both experiments and shared his results: Observe how the HMQC directly detects the proton resonance, which therefore the high-resolution dimension (F2). For example, his three lines are nicely resolved and turn out to be a doublet and a singlet. The carbon dimension is indirectly detected (F1), but the lines are resolved due to their spread in chemical shift. In the HETCOR experiment the carbons are directly detected and therefore in high resolution while the proton resolution suffers.

In the HETCOR experiment, the correlation between protons and hetero-nuclei proceeds by single quantum coherences while in HMQC the information is transferred via double and zero quantum coherences. These multiple quantum coherences are excited by more complicated pulse sequences and therefore more prone to pulse errors. Therefore the set up for the HMQC is more involved. The result may be worthwhile the effort.

HMQC Advantages - HETCOR Disadvantages:

1. The sensitivity of HMQC is 2 to 4 times greater than HETCOR for small molecules, 4 times for large molecules.
2. For the HMQC the 1H dimension is the "high resolution" dimension; while in HETCOR this is the 13C dimension. Since 1H chemical shifts span only ~10ppm, while 13C chemical shifts span ~200ppm and are normally well resolved, the "high resolution" dimension should be the 1H dimension.

HETCOR Advantages - HMQC Disadvantages:

1. The set-up of HMQC requires more time than the HETCOR.
2. To cancel artifacts, more scans must be acquired, so overall HMQC requires more time to run.
3. 1H-1H couplings are not removed in the regular HMQC, while they are removed in HETCOR (except coupling between non-equivalent methylenes). However, you can run a homonuclear decoupled version of the HMQC experiment, which requires additional set-up time.
4. Variations of the HETCOR can show only methines, or methines and methyls UP and methylenes DOWN. HMQC does not have these variations.