Apentix/AP Chemistry/Unit 2: Molecular and Ionic Compound Structure and Properties/Question
AP Chemistrymediummcq1 pt

Rotation about a carbon-carbon single bond is essentially free, but rotation about a double bond is severely restricted. Why?

A.Double bonds are longer, so the atoms collide during rotation
B.The second shared pair stiffens the sigma framework directly
C.Pi electrons repel nearby nuclei strongly enough to lock the angle
D.Rotation destroys the parallel p-orbital overlap that creates the pi bond

Explanation

Core Concept

A sigma bond cylinder looks the same at any viewing angle, so spinning about a single bond costs nothing. The pi bond exists only while the two unhybridized p orbitals remain parallel; twisting destroys their side-by-side overlap and would break the bond outright. Restoring alignment requires energy comparable to breaking the pi bond, so rotation stays frozen at room temperature.

Correct Answer

DRotation destroys the parallel p-orbital overlap that creates the pi bond

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