Proton Detected 1H—13C COSY HMQC

Historically, the HMQC (Heteronuclear Multiple Quantum Correlation) experiment was preceded by 

As mentioned in Chapter 3, the absolute sensitivity of an NMR experiment is given by the following 

There are only three cases possible for each carbon atom. If a line drawn encounters no cross peaks, then the carbon has no attached hydrogens. If the drawn line encounters only one cross peak, then the carbon may have either 1,2, or 3 protons attached if 2 protons are attached, then they are either chemical shift equivalent or they fortuitously overlap. If the horizontal line encounters two cross peaks, then we have the special case of diastereotopic protons attached to a methylene group. Much of this information will already be available to us from DEPT spectra (see Section 4.6) indeed, the HMQC spectrum should, whenever possible, be considered along with the DEPT. 

FIGURE 5.12 The bottom part of the figure is the HMQC spectrum for ipsenol while the top part of the figure is the HETCOR spectrum of ipsenol. 

Ipsenol has two methyl groups that appear as a triplet at 0.93 ppm in the proton spectrum. A closer look, however, at the inset reveals that it is a pair of coincidental doublets. Before moving on to the next section, consider the following question can the olefinic methylene carbon resonances be assigned on the basis of combined information from COSY and HMQC  

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