A side chain in organic chemistry and biochemistry is a part of a molecule that is attached to a core structure. Organic chemistry is a discipline within Chemistry which involves the scientific study of the structure properties composition reactions, and preparation Biochemistry is the study of the chemical processes in living Organisms It deals with the Structure and function of cellular components such as In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by An R group is a generic label for a side chain, which can be anything. However, in general, it is stable and covalently linked to the adjoining atom. The abbreviations R and R-group, which often refer to side chains, come from the word "radical", "rest," or "residue".