AP BIOLOGY

Detailed explanation-1: -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.

Detailed explanation-2: -The pi bond prevents rotation because of the electron overlap both above and below the plane of the atoms.

Detailed explanation-3: -Geometrical isomerism is a kind of stereoisomerism which is present in the compounds containing a double bond (C=C, C=N. N=N) and arise due to the restricted or frozen rotation about the double bond. The atoms or groups attached to the doubly bonded carbons must be different.

Detailed explanation-4: -Rotation around C-C single bond is not completely free and it is hindered by a small energy barrier of 1-20 kj/mol due to weak repulsive interaction between the adjacent bonds. Such type of repulsive interaction is called torsional strain.

Detailed explanation-5: -Isomerism due to hindered rotation: Due to hindered rotation around carbon-carbon double bond, the relative positions of groups attached to the double bonded carbon atoms get fixed. As a result, several alkenes can exhibit geometrical isomerism.