The structure of furan (C4H4O) is shown below. Determine the hybridization of the C atoms and the theoretical value of the C–C=C bond angle. Explain why the actual bond angle is smaller (106 º).

• A. Hybridization: sp²
  Theoretical bond angle: 120 º
  The actual bond angle is much smaller because the carbon atoms are constrained in a ring.
• B. Hybridization: sp³
  Theoretical bond angle: 109.5 º
  The actual bond angle is much smaller because the difference in atomic radius of the atoms.
• C. Hybridization: sp
  Theoretical bond angle: 180 º
  The actual bond angle is much smaller because the carbon atoms are constrained in a ring.
• D. Hybridization: sp²
  Theoretical bond angle: < 120 º
  The actual bond angle is much smaller because the difference in atomic radius of the atoms.

Answer: (A)