Geometrical Isomerism is a form of Stereo Isomerism. Stereo Isomerism are molecules that have the same molecular formula and the same sequence of bonded atoms, but different in the 3D orientations of their atoms in space. The key requirement for this is restricted rotation (i.e., C=C) , each carbon in restricted rotation must have attached to 2 different groups . Example : But-2-ene ( CH3-CH=CH=CH3 )

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The geometrical isomerism arises when atoms or groups are arranged differently in space, thanks to the restricted rotation of a bond or bonds within a molecule. When two compounds have the same molecular formula and the same structural formula but differ in the spatial arrangement of atoms or groups of atoms due to the restricted rotation of double bonds, about the only bond within the case of cyclic compounds, they are said to exhibit geometrical isomerism.

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