Substitution is a research area in the field of chemistry that involves the replacement of one atom or group of atoms in a molecule with another atom or group of atoms. This process can result in changes to the structure, properties, and reactivity of the molecule. Substitution reactions are a fundamental concept in organic chemistry and can occur through various mechanisms, such as nucleophilic substitution, electrophilic substitution, and radical substitution. Researchers study substitution reactions to better understand how molecules can be modified or transformed for various applications, such as drug development, materials science, and environmental chemistry.