BranchedChain

Branched chain is a term used in organic chemistry to describe carbon skeletons in which one or more carbon atoms form substituent branches off a continuous main chain rather than extending in a single linear direction. The main chain is treated as the parent structure, and the branches are alkyl groups such as methyl, ethyl, propyl, or larger substituents. Branched hydrocarbons are common among alkanes, cycloalkanes, and other hydrocarbon families; they contrast with straight-chain (unbranched) isomers that have the same molecular formula but a single continuous chain.

Nomenclature follows IUPAC rules that identify the longest carbon chain as the parent and describe branches with prefixes and locants. Examples include 2-methylpentane (a five-carbon chain with a methyl branch at carbon 2) and 3-ethylpentane (a pentane chain with an ethyl branch at carbon 3). In alkanes, branching generally lowers the boiling point compared with the linear isomer of the same formula due to reduced surface area and intermolecular interactions; branching also affects melting points, density, and reactivity. In polymers, branched structures reduce crystallinity and can alter viscosity and mechanical properties compared with linear analogs.

Branched chains are also a characteristic feature of branched-chain amino acids, a group of essential amino acids whose side chains are notably branched. The three best-known examples are leucine, isoleucine, and valine, collectively abbreviated BCAAs; they are important in protein synthesis and energy metabolism and are commonly used in nutritional supplements.