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Stereoisomers are compounds with the same molecular formula but differ from each other only in terms of the three-dimensional arrangement of the atoms or groups attached to them.

The cis and trans isomers are examples of stereoisomers.

• In the case of a cis isomer, both functional groups are present on the same side of the molecule.
• In the case of a trans isomer, both functional groups are on different sides of the molecule.

These are isomers that have the same molecular formula but different structures. In these isomers, the position of the functional groups may be different in different isomers.

Cis-1,3-diethylcyclobutane has the following structure:

Cis-1,3-diethylcyclobutane

(a) Trans-1,3-diethylcyclobutane is the stereoisomer of cis-1,3-diethylcyclobutane. It has the following structure:

Trans-1,3-diethylcyclobutane

(b) Cis-1,2-diethylcyclobutane is the constitutional isomer of cis-1,3-diethylcyclobutane. It has the following structure:

Cis-1,2-diethylcyclobutane