Sigma And Pi Bonds moving

[PatrickV]

Why is it that sigma ponds can't move and Pi bonds are able to move?

[WendyN_L2]

Sigma bonds are formed by end to end interaction so it has an electron density with cylindrical symmetry at the inter-nucleus axis so it can rotate. However with pi bonds the side ti side interaction is connected like = so one top and bottom. When one of the p orbitals rotates it will break one of those off. Hope that helps

[Jenny Han 3F]

I agree with the other comment; additionally, the top and bottom interactions occur because the pi-bonds have electron densities on each side of the internuclear axis, envisioned by the two lobes side-by-side and the orbitals that overlap (when there is more than one covalent bond).