An alkene/aromatic signal will often appear ~ 160–170 ppm in a ¹³C NMR spectrum. Why?

Identify the compound with molecular formula C₆H₁₀O that gives the following DEPT ¹³C NMR spectrum:

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The standard ¹³C NMR spectrum of phenyl propanoate is shown here. Predict the appearance of the DEPT-90 and DEPT-135 spectra.

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Different types of protons and carbons in alkanes tend to absorb at similar chemical shifts, making structure determination difficult. Explain how the ¹³C NMR spectrum, including the DEPT technique, would allow you to distinguish among the following four isomers.

How many signals would you expect to see in the 13C NMR of the following compounds? In each case, show which carbon atoms are equivalent in the ¹³C NMR.

(a) Show which carbon atoms correspond with which peaks in the 13C NMR spectrum of butan-2-one (Figure 13-45).

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Hexamethylbenzene undergoes free-radical chlorination to give one monochlorinated product (C₁₂H₁₇Cl) and four dichlorinated products (C₁₂H₁₆Cl₂). These products are easily separated by GC-MS, but the dichlorinated products are difficult to distinguish by their mass spectra. Draw the monochlorinated product and the four dichlorinated products, and explain how ¹³C NMR would easily distinguish among these compounds.

(a) Draw all six isomers of formula C₄H₈ (including stereoisomers).

(b) For each structure, show how many types of H would appear in the proton NMR spectrum.

(c) For each structure, show how many types of C would appear in the ¹³C NMR spectrum.

(d) If an unknown compound of formula C₄H₈ shows two types of H and three types of C, can you determine its structure from this information?