Question

What do you understand about geometrical isomerism? Write essential conditions for geometrical isomerism.

Answer 1

Hint: We know that the geometrical isomers can be defined as those isomers which occur in the molecules which have restricted rotation somewhere in the structure of the molecule. Some of the common examples of geometrical isomers may include the presence of carbon-carbon double bonds in a molecule.

Complete answer:
The molecules which are observed to have identical molecular formulae, but are known to have a different spatial arrangement of the atoms belonging to a molecule are known as Isomers. This definition of the isomers does not take into account any different kinds of arrangements which arise just because of the rotation of the molecule as a whole, or rotating around a certain specific bond. When the constituent atoms of a molecule are connected with each other in a different order, the phenomena are termed as the structural isomerism. In case of stereoisomerism, the constituent atoms of the isomers are being connected in the same order, but the structures still manage to possess a different kind of arrangement in the space. Geometric isomerism is one kind of stereoisomerism. Isomerism is the phenomenon in which two or more compounds have the same chemical formula but differ in chemical structures.
The chemical compounds that have identical chemical formulas but differ in properties and the arrangement of atoms in the molecule are called isomers i.e., they exhibit isomerism. Isomerism is of two types namely, Structural isomerism and stereoisomerism. In structural isomerism the functional groups and the atoms in the molecules of these isomers are bonded in different ways. Structural isomers have different IUPAC names although their chemical formulae are the same. The isomerism which arises due to frozen rotation about to bond in a molecule is known as geometrical or cis-trans isomerism. Conditions for geometrical isomerism: A compound will show geometrical isomerism if it fulfils the following two conditions: There should be restricted rotation about a bond in the molecule. Both substituents on each carbon about which rotation is frozen (restricted) should be different.

Note:
Remember that the pair of isomers have the same chemical formula but different chemical structures. Due to change in structures, at times they differ in their properties like boiling point, melting point etc. Geometrical isomerism is the type of isomerism based on the geometry of compounds.