Question

Assertion (A) In $H_{2}C==C{H}_2$ molecule, the rotation about carbon-carbon double bond $(C==C)$ is restricted
Reason (R) Rotation of one $C{H}_2$ fragment with respect to other interferes with maximum overlap of $p$-orbitals.

• A. Both $A$ and $R$ are correct; $R$ is the correct explanation of $A$.
• B. Both $A$ and $R$ are correct; $R$ is not the correct explanation of $A$.
• C. $A$ is correct; $R$ is incorrect.
• D. $R$ is correct; $A$ is incorrect.

Answer 1

Answer: (A)

In $C{H}_2==C{H}_2$ molecule, all the atoms must be in the same plane. The $p$-orbitals are mutually parallel and are perpendicular to the plane of the molecule.
Rotation of one $-C{H}_2$ fragment with respect to other interferes with maximum overlap of $p$-orbital and therefore such rotation about $C==C$ bond is restricted. Thus, both $A$ and $R$ are correct and $R$ is the correct explanation of $A$.