what is rotation about double bond and in what kind of organic compound is it possible?

A double bond consists of a sigma bond and a pi bond respectively.Pi bond is formed by sideways overlapping of unhybridized p-orbitals of two carbon atoms above and below the plane of carbon atoms.If one of the carbon atoms of double bond is rotated with respect to the other,the p-orbitals will no longer overlap and pi bond gets break,but such breaking of pi bond requires 251 kj/mole of energy which is not provided by collision of molecules at room temperature.As a result the rotation about a carbon-carbon double bond is not free but is strongly hindered or restricted.Thus there is an energy barrier to rotation which is much greater than in the case of a single bond.Such restricted rotation around the double bonds accounts for the cis-trans isomerism in appropriately substituted alkenes.For ex- 2-butene exist in cis and trans form.