Which type of atomic orbitals overlap to form $\pi$ bonds in organic molecules?

• A. Overlap of $s$ and $p$ orbitals
• B. Side-by-side overlap of unhybridized $p$ orbitals
• C. End-to-end overlap of hybridized $\mathrm{sp}$ orbitals
• D. End-to-end overlap of $s$ orbitals

Answer: (B)

Verified step by step guidance

1. Recall that a \( \pi \) bond is formed by the sideways (lateral) overlap of atomic orbitals, which is different from the end-to-end overlap that forms \( \sigma \) bonds.
2. Identify the types of orbitals involved in \( \pi \) bonding: \( \pi \) bonds arise from the side-by-side overlap of unhybridized \( p \) orbitals on adjacent atoms.
3. Understand that \( s \) orbitals overlap end-to-end to form \( \sigma \) bonds, not \( \pi \) bonds, and hybridized orbitals like \( sp \), \( sp^2 \), or \( sp^3 \) typically form \( \sigma \) bonds.
4. Recognize that the unhybridized \( p \) orbitals remain perpendicular to the plane of the molecule and overlap sideways to create the \( \pi \) bond, which provides the characteristic electron density above and below the bonding axis.
5. Conclude that the correct description of \( \pi \) bond formation is the side-by-side overlap of unhybridized \( p \) orbitals.