In the indigo molecule, what type of hybrid orbitals are used by the carbon atoms?

• A. $sp{3}^{}$ hybrid orbitals
• B. Unhybridized $p$ orbitals only
• C. $sp$ hybrid orbitals
• D. $sp{2}^{}$ hybrid orbitals

Answer: (D)

Verified step by step guidance

1. Step 1: Identify the bonding environment of carbon atoms in the indigo molecule. Indigo contains conjugated double bonds and aromatic rings, which influence the hybridization of carbon atoms.
2. Step 2: Recall that carbon atoms forming double bonds or participating in aromatic systems typically use \(s p^{2}\) hybrid orbitals. This allows for three sigma bonds in a trigonal planar arrangement and one unhybridized \(p\) orbital for pi bonding.
3. Step 3: Understand that \(s p^{3}\) hybridization corresponds to tetrahedral geometry with single bonds only, which is not the case for carbons in indigo due to the presence of double bonds and conjugation.
4. Step 4: Recognize that unhybridized \(p\) orbitals alone are not sufficient to describe the bonding framework of carbon atoms in indigo, as sigma bonds require hybrid orbitals.
5. Step 5: Conclude that the carbon atoms in indigo use \(s p^{2}\) hybrid orbitals to form sigma bonds and maintain the planar structure necessary for conjugation and aromaticity.