What is meant by restricted rotation around of carbon-carbon double bond? What type of isomerism does it lead to?

What is meant by restricted rotation around of carbon-carbon double bond? What type of isomerism does it lead to?
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Ans. The carbon-carbon double bond in alkene contains one sigma bond and one pi-bond. The Pibond involves the overlapping of unhybridised p orbital of two carbon atom .The rotation around the carbon-carbon double bond is only possible only if Pi bond breaks. The breaking of pi bond required 251KJ/M energy which is not provide by the molecular collision at room temperature .Therefore ,the atom or group attached to the double bonded carbon atoms cannot rotate about. In other words, the free rotation around C=C double bond is restricted, which gives rise to Geometrical Isomerism.
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