How To Read HETCOR Spectra

2-Nitropropane. Fignre 9.16 is an example of a simple HETCOR plot. In this case, the sample substance is 2-nitropropane. 

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Each spot on the HETCOR plot has been labeled with a number, and lines have been drawn to help you see the correlations between proton peaks and carbon peaks. The carbon peak at 23 ppm and the proton doublet at 0.92 ppm correspond to the methyl groups (1) the carbon peak at 25 ppm and the proton multiplet at 1.69 ppm correspond to the methine position (2) and the carbon peak at 

4-Methyl-2-Pentanol. Eigure 9.18 is a final example that illustrates some of the power of the HETCOR technique for 4-methyl-2-pentanol. Lines have been drawn on the spectrum to help you find the correlations. 

This molecule has a stereocenter at carbon 2. An examination of the HETCOR plot for 4-methyl-2-pentanol reveals two spots that correspond to the two methylene protons on carhon 3. At 48 ppm on the carbon axis, two contour spots appear, one at about 1.20 ppm on the proton axis and the other at about 1.40 ppm. The HETCOR plot is telling us that there are two nonequivalent protons attached to carbon 3. If we examine a Newman projection of this molecule, we find that the presence of the stereocenter makes the two methylene protons (a and b) nonequivalent (see Sections 5.14 and 5.15). As a result, they appear at different values of chemical shift. 

A great many advanced techniques can be applied to complex molecules. We have introduced only a few of the most important ones here. As computers become faster and more powerful, as chemists evolve their understanding of what different pulse sequences can achieve, and as scientists write more sophisticated computer programs to control those pulse sequences and treat data, it will become possible to apply NMR spectroscopy to increasingly complex systems. 

610 Nuclear Magnetic Resonance Spectroscopy Part Five Advanced NMR Techniques 

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