In organic chemistry, isomers are molecules that have the same molecular formula but different arrangements of atoms in space. There are two main types of isomers: structural isomers and stereoisomers.1. Structural Isomers also known as constitutional isomers : These isomers have the same molecular formula but differ in the connectivity of their atoms, meaning the order in which the atoms are bonded together. Structural isomers have different physical and chemical properties because their atoms are connected in different ways, leading to different functional groups and overall molecular structures.Example 1: Butanol and isobutanolBoth have the molecular formula C4H10O, but their structures are different.- Butanol: CH3-CH2-CH2-CH2-OH- Isobutanol: CH3 2-CH-CH2-OHIn butanol, the hydroxyl group -OH is attached to a terminal carbon, while in isobutanol, the hydroxyl group is attached to a non-terminal carbon.2. Stereoisomers: These isomers have the same molecular formula and the same connectivity of atoms, but they differ in the spatial arrangement of atoms in three-dimensional space. Stereoisomers can be further divided into two subcategories: enantiomers and diastereomers.Example 2: R - and S -lactic acidBoth have the molecular formula C3H6O3 and the same connectivity of atoms, but they differ in the spatial arrangement of atoms around the chiral center the carbon atom with four different substituents .- R -lactic acid: The hydroxyl group -OH is on the right side of the chiral center when using the Cahn-Ingold-Prelog priority rules.- S -lactic acid: The hydroxyl group -OH is on the left side of the chiral center when using the Cahn-Ingold-Prelog priority rules.These two isomers are enantiomers, which are non-superimposable mirror images of each other. They have the same physical properties but can have different biological activities due to their interactions with chiral biomolecules.In summary, the relationship between structural isomers and stereoisomers lies in their difference in atom connectivity and spatial arrangement. Structural isomers have different atom connectivity, while stereoisomers have the same atom connectivity but different spatial arrangements.