Side chain

This article is about the chemistry term. For the audio engineering term, see dynamic range compression#Side-chaining.

In organic chemistry and biochemistry, a side chain is a chemical group that is attached to a core part of the molecule called "main chain" or backbone. The placeholder R is often used as a generic placeholder for alkyl(saturated Hydrocarbons) group side chains in chemical structure diagrams. To indicate other non-carbon groups in structure diagrams, X, Y, or Z is often used. The R, historically, is derived from radical or rest.^{[citation needed]}

In polymer science, the side chain or pendant chain is oligomeric or polymeric offshoot extends from the backbone chain of a polymer. Side chains have noteworthy influence on a polymer's properties, mainly its crystallinity and density. An oligomeric branch may be termed a short-chain branch and a polymeric branch may be termed a long-chain branch. Side groups are different from side chains; they are neither oligomeric nor polymeric.

In proteins (composed of amino acids) the side chains are attached to the alpha-carbon atoms of the amide backbone.

See also

• Substituent
• Functional group
• Alkyl