The restricted rotation around carbon-carbon double bond in 2-butene is due to
  1. Overlap of twop-orbitals
  2. Overlap of onep and onesp2hybridized orbital
  3. Overlap of twosp2 hybridized orbital
  4. Overlap of ones and onesp2hybridized orbitals
Ans and Explanation

Dear Student,

Rotation through C=C bond in 2-butene is restricted. The two carbons of the C=C bond are sp‚Äč2 hybridised. The three hybrid sp2 orbitals lie in one plane. These three orbitals are used to form three σ bonds that are co-planar.The unhybridised p-orbital at each carbon atom forms a π bond. The π cloud spreads over both carbon atoms above and below the plane of the σ bond. The overlap of two unhybridised p-orbitals is maximum when they are parallel to each other. This is possible if all the four groups along with the two carbon atoms are coplanar.
Hence, any change in this coplanar geometry by twisting the C=C bond would make the molecule unstable. Therefore, rotation around C=C bond is restricted.

Since, this restricted rotation is due to the formation of π bond, which is formed by the overlap of two p-orbitals, so the correct answer is (1)

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