What is Substituent?
In [[organic chemistry]] and [[biochemistry]], '''substituent''' is the name for a single [[atom]] or for a group of atoms that take the position of another atom in a [[molecule]]. They replace this atom. This [[chemical reaction|reaction]] is called a [[substitution reaction]]. The atom or group of atoms that gets replaced is called the [[leaving group]]. The terms '''substituent''', '''side chain''', '''group''', '''branch''', or '''[[pendant group]]''' are used in the same way to describe [[branch]]es from a parent [[structure]].<ref>{{cite book|title=Organic Chemistry Demystified|url=https://books.google.com/books?id=yVPcSIn5xjAC&pg=PT88|author=D.R. Bloch|year=2006| publisher=Mcgraw-hill |isbn = 9780071459204}}</ref> These terms have different meanings in [[polymer]] chemistry.<ref>{{cite journal|url=http://goldbook.iupac.org/src_PAC1996682287.html|title=PAC, 1996, 68, 2287. Glossary of basic terms in polymer science (IUPAC Recommendations 1996)|doi=10.1351/pac199668122287|publisher=IUPAC Gold Book|s2cid=98774337}} This distinguishes a ''pendant group'' as neither oligomeric nor polymeric, whereas a ''pendant chain'' must be oligomeric or polymeric.</ref> In [[polymers]], side chains extend from a backbone structure, while they are [[wikt:attach|attached]] to the [[alpha carbon]] atoms of the [[amino acid]] backbone in [[protein]]s. Organic chemistry has [[rules]] for naming compounds with substituent groups. The substituent group is listed first with a [[suffix]] to describe how it is attached to the main [[carbon]] chain. The suffix '''-yl''' is used when naming [[organic compound]]s that contain a [[single bond]] replacing one [[hydrogen]]. '''-ylidene''' and '''-ylidyne''' are used for [[double bond]]s and [[triple bond]]s respectively. When naming [[hydrocarbon]]s that contain a substituent, position numbers may be used. These number will indicate which carbon atom the substituent is attached to. One case where this information is needed is that of [[isomer]]s. The phrases '''most-substituted''' a