What type of bonding interactions are possible at positions (i) O-H and (iii) N+, respectively, of the following drug?

Question

BlackTom AI · Accepted Answer

The O–H group in morphine is a classic hydrogen-bonding functional group, and the positively charged nitrogen (N+) is a site for electrostatic (ionic) interactions.

1. Relevant knowledge points and concepts
- Hydroxyl groups (O–H) have a polarized O–H bond: oxygen is electronegative with lone pairs and the hydrogen is partially positive, so O–H can act as a hydrogen-bond donor (and the oxygen can also act as a hydrogen-bond acceptor via its lone pairs).
- A protonated nitrogen (N+; an ammonium-like center) carries a formal positive charge and interacts strongly with negatively charged partners via ionic (electrostatic) interactions. Protonated nitrogens can also participate in hydrogen bonding when an N–H is present, but their defining interaction with oppositely charged groups is ionic.

2. Step-by-step reasoning
- Identify position (i): labeled O–H. That group can donate a hydrogen to an electron-rich acceptor (e.g., carbonyl oxygen, water, amino acid side-chain acceptors). Thus the primary interaction expected is hydrogen bonding.
- Identify position (iii): labeled N+. This indicates the tertiary amine is protonated (positively charged). A positively charged center will form strong electrostatic attractions with negatively charged species (e.g., carboxylate side chains in proteins). Those are ionic interactions rather than mere dipole–dipole or hydrophobic contacts.

3. Calculations
- No numerical calculation is required; reasoning is based on functional-group chemistry and charge.

4. Why the correct answer is correct
- O–H → hydrogen bond (donor). N+ → ionic interactions (electrostatic attraction to anions). This matches option (a).

5. Why the other options are incorrect
- (b) Ion–dipole and dipole–dipole: O–H is better described as hydrogen bonding (a specific strong dipole–H interaction), and N+ primarily gives ionic interactions rather than only ion–dipole/dipole–dipole.
- (c) Van der Waals and hydrogen bond: O–H is not primarily van der Waals (it forms hydrogen bonds), and N+ is ionic rather than primarily a hydrogen-bonding site here.
- (d) Van der Waals and ionic: again O–H is hydrogen-bonding, not hydrophobic van der Waals.

Conclusion: The correct choice is a. Hydrogen bond and ionic interactions, which matches the provided answer.

What type of bonding interactions are possible at positions (i) O-H and (iii) N+, respectively, of the following drug?单项选择题

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