In the context of the DEPT-90 NMR experiment, which carbon atoms in morphine would produce a signal on the spectrum?

• A. Only the methylene carbons (${\mathrm{CH}}_2$)
• B. All carbons except quaternary carbons
• C. Only the methine carbons (${\mathrm{CH}}_1$)
• D. Only the methyl carbons (${\mathrm{CH}}_3$)

Answer: (C)

Verified step by step guidance

1. Understand that the DEPT (Distortionless Enhancement by Polarization Transfer) NMR experiment is used to differentiate carbon types based on the number of attached hydrogens.
2. Recall that DEPT-90 specifically shows signals only for carbons bonded to exactly one hydrogen atom, which are called methine carbons (\$\mathrm{CH}\$).
3. Identify the types of carbons in morphine: methyl (\$\mathrm{CH}_3\$), methylene (\$\mathrm{CH}_2\$), methine (\$\mathrm{CH}\$), and quaternary (no hydrogens attached).
4. Since DEPT-90 detects only methine carbons, only those carbons in morphine with one hydrogen attached will appear in the DEPT-90 spectrum.
5. Therefore, the carbons that produce signals in the DEPT-90 spectrum of morphine are exclusively the methine carbons (\$\mathrm{CH}\$).