Stereochemistry is a branch of chemistry that focuses on the spatial arrangement of atoms within molecules. It examines how different arrangements can lead to different properties and behaviors of compounds, even if they have the same molecular formula. This is crucial in fields like pharmaceuticals, where the effectiveness of a drug can depend on its specific 3D structure. Key concepts in stereochemistry include isomers, which are compounds with the same formula but different arrangements, and chirality, where a molecule cannot be superimposed on its mirror image. Understanding these concepts helps chemists design and synthesize compounds with desired characteristics.