Side chain




This article is about the side chain of any type of long molecule. For the substitution of an atom or chemical group for a hydrogen atom on a hydrocarbon chain, see Substituent.

This article is about the chemistry term. For the audio engineering term, see dynamic range compression § Side-chaining. For blockchain-extension technology, see Sidechain (ledger).


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IUPAC definition


Branch
Side-chain
Pendant chain
An oligomeric or polymeric offshoot from a macromolecular chain.

Notes



  1. An oligomeric branch may be termed a short-chain branch.

  2. A polymeric branch may be termed a long-chain branch.[1]




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 side chain is a hydrocarbon branching element of a molecule that is attached to a larger hydrocarbon backbone. It is one factor in determining a molecule's properties and reactivity.[2] A side chain is also known as a pendant chain, but a pendant group (side group) has a different definition.




Contents






  • 1 Conventions


  • 2 History


  • 3 Usage


    • 3.1 Organic chemistry


    • 3.2 Biochemistry




  • 4 See also


  • 5 References





Conventions


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 are often used.



History


The R symbol was introduced by 19th-century French chemist Charles Frédéric Gerhardt, who advocated its adoption on the grounds that it would be widely recognizable and intelligible given its correspondence in multiple European languages to the initial letter of one or more words already used to denote the concept and sharing the meaning "root" or "residue": French racine ("root") and résidu ("residue"), these terms' respective English translations along with radical (itself derived from Latin radix below), Latin radix ("root") and residuum ("residue"), and German Rest ("remnant" and, in the context of chemistry, both "residue" and "radical").[3]



Usage



Organic chemistry


In polymer science, the side chain of an 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.[4]



Biochemistry


In proteins, which are composed of amino acid residues, the side chains are attached to the alpha-carbon atoms of the amide backbone. The side chain connected to the alpha-carbon is specific for each amino acid and is responsible for determining charge and polarity of the amino acid. The amino acid side chains are also responsible for many of the interactions that lead to proper protein folding and function.[5] Amino acids with similar polarity are usually attracted to each other, while nonpolar and polar side chains usually repel each other. Nonpolar/polar interactions can still play an important part in stabilizing the secondary structure due the relatively large amount of them occurring throughout the protein.[6]




Table of amino acids



See also



  • Alkyl

  • Backbone chain

  • Branching (polymer chemistry)

  • Functional group

  • Pendant group

  • Substituent



References





  1. ^ "Glossary of basic terms in polymer science (IUPAC Recommendations 1996)" (PDF). Pure and Applied Chemistry. 68 (12): 2287–2311. 1996. doi:10.1351/pac199668122287..mw-parser-output cite.citation{font-style:inherit}.mw-parser-output q{quotes:"""""""'""'"}.mw-parser-output code.cs1-code{color:inherit;background:inherit;border:inherit;padding:inherit}.mw-parser-output .cs1-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-limited a,.mw-parser-output .cs1-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/d/d6/Lock-gray-alt-2.svg/9px-Lock-gray-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Lock-red-alt-2.svg/9px-Lock-red-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration{color:#555}.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration span{border-bottom:1px dotted;cursor:help}.mw-parser-output .cs1-hidden-error{display:none;font-size:100%}.mw-parser-output .cs1-visible-error{font-size:100%}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-right{padding-right:0.2em}


  2. ^ Wade, L.G. (2010). Organic Chemistry, 7th Edition. Upper Saddle River, NJ: Pearson Prentice Hall. pp. 70–78. ISBN 978-0-321-59231-6.


  3. ^ Jensen W.B., Journal of Chemical Education 87, 360 (2010)


  4. ^ Chemistry, International Union of Pure and Applied. IUPAC Compendium of Chemical Terminology. iupac.org. IUPAC. doi:10.1351/goldbook.B00720.


  5. ^ Voet, Donald; Voet, Judith; Pratt, Charlotte (2013). Fundamentals of Biochemistry: Life at the Molecular Level (Fourth ed.). Hoboken, NJ: John Wiley & Sons, Inc. ISBN 9781118129180.


  6. ^ Andrew, C. D.; Penel, S.; Jones, G. R.; Doig, A. J. (2001-12-01). "Stabilizing nonpolar/polar side-chain interactions in the alpha-helix". Proteins. 45 (4): 449–455. ISSN 0887-3585. PMID 11746692.















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