How do you identify isomers of a compound?

Isomers are identified by comparing the molecular formula and structural arrangement of atoms in different compounds.

Isomers are compounds that have the same molecular formula but different structural formulas. This means they have the same number and type of atoms, but these atoms are arranged differently. There are two main types of isomers: structural (or constitutional) isomers and stereoisomers.

Structural isomers have the same molecular formula but different connectivity of atoms. For example, butane and isobutane are structural isomers. They both have the molecular formula C4H10, but the arrangement of carbon atoms differs. In butane, the carbon atoms are arranged in a straight chain, while in isobutane, there is a branched chain.

Stereoisomers, on the other hand, have the same molecular formula and the same connectivity of atoms, but different spatial arrangements. They are further divided into two types: geometric (or cis-trans) isomers and optical isomers. Geometric isomers occur in compounds with restricted rotation (like double bonds or ring structures), where atoms or groups of atoms can occupy different positions in space. For example, in 2-butene, the two methyl groups can be on the same side of the double bond (cis-2-butene) or on opposite sides (trans-2-butene).

Optical isomers are molecules that are mirror images of each other, like left and right hands. They are named so because they can rotate plane-polarised light in different directions. They occur in molecules that have a chiral centre, usually a carbon atom with four different groups attached to it.

To identify isomers, you need to first determine the molecular formula of the compounds. Then, examine the structural arrangement of atoms. If the arrangement differs, they are structural isomers. If the arrangement is the same but the spatial orientation differs, they are stereoisomers.