H—13C COSY HETCOR

A look at the extreme low-frequency portion of this COSY spectrum reveals an unexpected interaction. It seems that either one or both of the methyl singlets shows coupling to resonances at 1.65 and at 2.09 ppm. This apparent conflict can be resolved by a close examination of the methyl singlet at 0.98 ppm. There is an unusually low-frequency multiplet, partially buried by the methyl singlets, that we had initially overlooked. This type of unexpected dividend is common in correlation spectra both partially and completely obscured resonances usually reveal themselves in 2-D spectra (see HETCOR, Section 6.6). Before continuing our discussion of caryophyllene oxide, let us consider ]H—13C correlations and how H— H correlations interplay with H—13C correlations. 

The HETCOR experiment correlates l3C nuclei with directly attached (i.e., coupled) protons these are one- 

There are only three cases possible for each carbon atom. If a line drawn down 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 dropline 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 5.5) indeed, the HETCOR should, whenever possible, be considered along with the DEPT. 

In ipsenol, there are four methylene groups, all of which possess diastereotopic pairs of protons. Resonance for two of these methylene groups occurs in the carbon spectrum at 41 and 47 ppm. Note with which protons these carbon atoms are correlated and compare these results with what we have found with COSY. As we expect, the results here confirm our assignments from COSY and help build an ever-strengthening basis for our assignments. The other two methylene carbon 

The olefinic methylene (protons and carbon) and the three methyl groups (protons and carbons) are trivial assignments, and they correspond with our previous discussion. Of more interest and of greater utility, we assign the three methine protons the doublet of dou- 

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