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 hydrocarbon) 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, was introduced by 19th-century French chemist Charles Frédéric Gerhardt and may be derived from radical, or from residue and its German equivalent Rest.
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.
Famous quotes containing the words side and/or chain:
“Some things in life are bad
They can really make you mad
Other things just make you swear and curse
When you’re chewing on life’s gristle
Don’t grumble, give a whistle
And this’ll help turn things out for the best ...
And ... always look on the bright side of life.”
—Monty Python’s Flying Circus. Mr. Frisbee III (Eric Idle)
“The years seemed to stretch before her like the land: spring, summer, autumn, winter, spring; always the same patient fields, the patient little trees, the patient lives; always the same yearning; the same pulling at the chain—until the instinct to live had torn itself and bled and weakened for the last time, until the chain secured a dead woman, who might cautiously be released.”
—Willa Cather (1873–1947)