{{Short description|Cyclic chemical group (–C6H5)}} thumb|140px|Phenyl radical group
In organic chemistry, the '''phenyl group''', or '''phenyl ring''', is a cyclic group of atoms with the formula {{chem2|C6H5\s}}, and is often represented by the pseudoelement symbol '''Ph''' (archaically '''φ''') or '''Ø'''. The phenyl group is closely related to benzene and can be viewed as a benzene ring, minus a hydrogen atom, which may be replaced by some other element or compound to serve as a functional group. A phenyl group has six carbon atoms bonded together in a hexagonal planar ring, five of which are bonded to individual hydrogen atoms, with the remaining carbon bonded to a substituent. Phenyl groups are commonplace in organic chemistry.<ref name=March>{{cite book |last=March |first=Jerry |title=Advanced organic chemistry: reactions, mechanisms, and structure |url=https://archive.org/details/advancedorganicc04edmarc |url-access=registration |date=1992 |publisher=Wiley |location=New York |isbn=978-0-471-60180-7 |edition=4th}}</ref> Although often depicted with alternating double and single bonds, the phenyl group is chemically aromatic and has equal bond lengths between carbon atoms in the ring.<ref name=March/><ref name="MSU">{{cite web |work=Virtual Textbook of Organic Chemistry |title=Aromaticity. Benzene and Other Aromatic Compounds |publisher=Michigan State University |url=http://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/react3.htm}}</ref>
==Nomenclature== Usually, a "phenyl group" is synonymous with {{chem2|C6H5\s}} and is represented by the symbol Ph (archaically, Φ), or Ø. Benzene is sometimes denoted as PhH. Phenyl groups are generally attached to other atoms or groups. For example, triphenylmethane ({{chem2|Ph3CH}}) has three phenyl groups attached to the same carbon center. Many or even most phenyl compounds are not described with the term "phenyl". For example, the chloro derivative {{chem2|C6H5Cl}} is normally called chlorobenzene, although it could be called phenyl chloride. In special (and rare) cases, isolated phenyl groups are detected: the phenyl anion ({{chem2|C6H5-}}), the phenyl cation ({{chem2|C6H5+}}), and the phenyl radical ({{chem|C|6|H|5|•}}).
Although Ph and phenyl uniquely denote {{chem2|C6H5\s}}, substituted derivatives also are described using the phenyl terminology. For example, {{chem2|C6H4NO2\s}} is nitrophenyl, and {{chem2|C6F5\s}} is pentafluorophenyl. Monosubstituted phenyl groups (that is, disubstituted benzenes) are associated with electrophilic aromatic substitution reactions and the products follow the arene substitution pattern. So, a given substituted phenyl compound has three isomers, ''ortho'' (1,2-disubstitution), ''meta'' (1,3-disubstitution) and ''para'' (1,4-disubstitution). A disubstituted phenyl compound (trisubstituted benzene) may be, for example, 1,3,5-trisubstituted or 1,2,3-trisubstituted. Higher degrees of substitution, of which the pentafluorophenyl group is an example, exist and are named according to IUPAC nomenclature.
===Etymology=== Phenyl is derived {{ety|fr|phényle}}, which in turn derived {{ety|el|''φαίνω'' (phaino)|shining}}, as the first phenyl compounds named were byproducts of making and refining various gases used for lighting.<ref>{{cite web |url=http://www.oxforddictionaries.com/us/definition/american_english/phenyl |archive-url=https://web.archive.org/web/20130216194714/http://oxforddictionaries.com/us/definition/american_english/phenyl |url-status=dead |archive-date=February 16, 2013 |title=phenyl |work=English by Lexico Dictionaries |access-date=24 July 2019}}</ref> According to McMurry, "The word is derived {{ety|el|pheno|I bear light}}, commemorating the discovery of benzene by Michael Faraday in 1825 from the oily residue left by the illuminating gas used in London street lamps."<ref>{{cite book |last1=McMurry |first1=John E. |title=Organic Chemistry, Enhanced Edition |date=2009 |publisher=Cengage Learning |isbn=9781111790042 |page=518 |url=https://books.google.com/books?id=Ffs7AAAAQBAJ |language=en}}</ref>
==Structure, bonding, and characterization== Phenyl compounds are derived from benzene ({{chem2|C6H6}}), at least conceptually and often in terms of their production. In terms of its electronic properties, the phenyl group is related to a vinyl group. It is generally considered an inductively withdrawing group (-''I''), because of the higher electronegativity of sp<sup>2</sup> carbon atoms, and a resonance donating group (+''M''), due to the ability of its π system to donate electron density when conjugation is possible.<ref>{{Cite journal|last=Hansch|first=Corwin.|last2=Leo|first2=A.|last3=Taft|first3=R. W.|date=1991-03-01|title=A survey of Hammett substituent constants and resonance and field parameters|journal=Chemical Reviews|volume=91|issue=2|pages=165–195|doi=10.1021/cr00002a004|issn=0009-2665}}</ref> The phenyl group is hydrophobic. Phenyl groups tend to resist oxidation and reduction. Phenyl groups (like all aromatic compounds) have enhanced stability in comparison to equivalent bonding in aliphatic (non-aromatic) groups. This increased stability is due to the unique properties of aromatic molecular orbitals.<ref name="MSU"/>
The bond lengths between carbon atoms in a phenyl group are approximately 1.4 Å.<ref name="Hameka1987">{{cite journal|last1=Hameka|first1=Hendrik F.|title=Computation of the structures of the phenyl and benzyl radicals with the UHF method|journal=The Journal of Organic Chemistry|volume=52|issue=22|year=1987|pages=5025–5026|issn=0022-3263|doi=10.1021/jo00231a035}}</ref>
In <sup>1</sup>H-NMR spectroscopy, protons of a phenyl group typically have chemical shifts around 7.27 ppm. These chemical shifts are influenced by aromatic ring current and may change depending on substituents.
==Preparation, occurrence, and applications== Phenyl groups are usually introduced using reagents that behave as sources of the phenyl anion or the phenyl cation. Representative reagents include phenyllithium ({{chem2|C6H5Li}}) and phenylmagnesium bromide ({{chem2|C6H5MgBr}}). Electrophiles are attacked by benzene to give phenyl derivatives: :<chem>C6H6 + E+ -> C6H5E + H+</chem> where {{chem2|E+}} (the "electrophile") = {{chem2|Cl+, NO2+, SO3}}. These reactions are called electrophilic aromatic substitutions. <gallery caption="Representative compounds containing phenyl groups" widths="180px" heights="120px" perrow="5"> File: Atorvastatin.svg|Atorvastatin (Lipitor), a blockbuster drug featuring two phenyl and one ''p''-fluorophenyl groups. It is used to lower cholesterol in people with hypercholesterolaemia. File: Fexofenadine2DCSD.svg|Fexofenadine (Allegra, Telfast), another blockbuster drug, which features a diphenylmethyl group as well as a ''p''-phenylene ({{chem2|C6H4}}) group. It is an antihistamine used to treat allergies. File: Phenylalanin_-_Phenylalanine.svg|Phenylalanine, a common amino acid. File: Bifenyl.svg|Biphenyl, consisting of two phenyl groups. The two rings tend not to be coplanar. File: Chlorobenzene2.svg|Chlorobenzene (or phenyl chloride), a solvent. </gallery>
Phenyl groups are found in many organic compounds, both natural and synthetic (see figure). Most common among natural products is the amino acid phenylalanine, which contains a phenyl group. A major product of the petrochemical industry is "BTX" consisting of benzene, toluene, and xylene - all of which are building blocks for phenyl compounds. The polymer polystyrene is derived from a phenyl-containing monomer and owes its properties to the rigidity and hydrophobicity of the phenyl groups. Many drugs as well as many pollutants contain phenyl rings. One of the simplest phenyl-containing compounds is phenol, {{chem2|C6H5OH}}. It is often said the resonance stability of phenol makes it a stronger acid than that of aliphatic alcohols such as ethanol (p''K''<sub>a</sub> = 10 vs. 16–18). However, a significant contribution is the greater electronegativity of the ''sp''<sup>2</sup> alpha carbon in phenol compared to the ''sp''<sup>3</sup> alpha carbon in aliphatic alcohols.<ref name="Silva2009">{{cite journal|last1=Silva|first1=Pedro Jorge|title=Inductive and Resonance Effects on the Acidities of Phenol, Enols, and Carbonyl α-Hydrogens|journal=The Journal of Organic Chemistry|volume=74|issue=2|year=2009|pages=914–916|issn=0022-3263|doi=10.1021/jo8018736|pmid=19053615|hdl=10284/3294|hdl-access=free}}</ref>
==References== {{Reflist}}
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Category:Aryl groups Category:Phenyl compounds