Question

Give a short note on geometrical isomerism..

Answer 1

Geometric Isomerism results most commonly from Carbon-Carbon double bonds. The important property which introduces the feature is the inability of the Carbon atoms to rotate relative to one another about the double bond. The lack of rotation means the same groups can be attached in different ways to achieve diastereomers. The molecules have identical connectivity so can't be described as structural isomers. 
There are two ways to name compounds of this kind. When two of the four groups attached to the carbons involved are hydrogen, the cis and trans notation can be used. When the other two constituents are on the same side of the molecules name is given the prefix 'cis'. Otherwise if the constituents are on opposite sides the prefix is 'trans'. 

Answer 2

Answer :

The isomer which have same structural formula but different spatial arrangements of atom or groups across the C-C double bond are known as geometrical isomer and the phenomena is known as geometrical isomerism.

Geometrical isomerism can be classified into two types -

1. Cis - Isomer

2. Trans - Isomer

⇒ Cis - Isomer

The isomer in which the similar atom or group are present on the same side of C-C double bond are known as cis - isomer.

Refer to the attachment for example.

⇒ Trans - Isomer

The isomer in which the similar atom or group are present on the opposite side of C-C double bond are known as trans - isomer.

Refer to the attachment for example.

Conditions for a molecule to show geometrical isomerism -

1. The compound must contain at least one C-C double bond.

2. To each carbon atom, the atom or group attached should be different.