Which of the following atoms in histrionicotoxin 283a are ${\mathrm{sp}}^2$-hybridized?

• A. All carbon atoms in the molecule
• B. Only the nitrogen atoms in the molecule
• C. All carbon atoms in the aromatic ring and the imine nitrogen
• D. Only the oxygen atoms

Answer: (C)

Verified step by step guidance

1. Step 1: Understand what sp\textsuperscript{2} hybridization means. An atom is sp\textsuperscript{2} hybridized if it forms three sigma bonds and has one unhybridized p orbital, typically seen in atoms involved in double bonds or aromatic systems.
2. Step 2: Identify the atoms in the molecule that are part of an aromatic ring or double bonds. In aromatic rings, all carbon atoms are sp\textsuperscript{2} hybridized because they participate in a conjugated pi system with alternating double bonds.
3. Step 3: Look for nitrogen atoms that are part of double bonds, such as imine nitrogens (C=N). These nitrogens are also sp\textsuperscript{2} hybridized because they form a double bond and have a lone pair in an unhybridized p orbital.
4. Step 4: Recognize that oxygen atoms in typical functional groups like alcohols or ethers are usually sp\textsuperscript{3} hybridized, while oxygen in carbonyl groups (C=O) is sp\textsuperscript{2} hybridized. Determine the hybridization of oxygen atoms based on their bonding environment.
5. Step 5: Conclude that the atoms which are sp\textsuperscript{2} hybridized in histrionicotoxin 283a are all carbon atoms in the aromatic ring and the imine nitrogen, as these fit the criteria of sp\textsuperscript{2} hybridization due to their bonding and electronic structure.