In organic chemistry, the phenyl group, or phenyl ring, is a cyclic group of atoms with the formula C6H5, and is often represented by the symbol Ph (archaically
Nomenclature
editUsually, a "phenyl group" is synonymous with C6H5− and is represented by the symbol Ph or, archaically,
6H•
5).
Although Ph and phenyl uniquely denote C6H5−, substituted derivatives also are described using the phenyl terminology. For example, C6H4NO2− is nitrophenyl, and C6F5− 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
editPhenyl is derived from French phényle, which in turn derived from Greek φαίνω (phaino) 'shining', as the first phenyl compounds named were byproducts of making and refining various gases used for lighting.[3] According to McMurry, "The word is derived from Greek 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."[4]
Structure, bonding, and characterization
editPhenyl compounds are derived from benzene (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 sp2 carbon atoms, and a resonance donating group (+M), due to the ability of its
The bond lengths between carbon atoms in a phenyl group are approximately 1.4 Å.[6]
In 1H-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
editPhenyl groups are usually introduced using reagents that behave as sources of the phenyl anion or the phenyl cation. Representative reagents include phenyllithium (C6H5Li) and phenylmagnesium bromide (C6H5MgBr). Electrophiles are attacked by benzene to give phenyl derivatives:
where E+ (the "electrophile") = Cl+, NO+2, SO3. These reactions are called electrophilic aromatic substitutions.
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Atorvastatin (Lipitor), a blockbuster drug featuring two phenyl and one p-fluorophenyl groups. It is used to lower cholesterol in people with hypercholesterolaemia.
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Fexofenadine (Allegra, Telfast), another blockbuster drug, which features a diphenylmethyl group as well as a p-phenylene (C6H4) group. It is an antihistamine used to treat allergies.
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Phenylalanine, a common amino acid.
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Biphenyl, consisting of two phenyl groups. The two rings tend not to be coplanar.
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Chlorobenzene (or phenyl chloride), a solvent.
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, C6H5OH. It is often said the resonance stability of phenol makes it a stronger acid than that of aliphatic alcohols such as ethanol (pKa = 10 vs. 16–18). However, a significant contribution is the greater electronegativity of the sp2 alpha carbon in phenol compared to the sp3 alpha carbon in aliphatic alcohols.[7]
References
edit- ^ a b March, Jerry (1992). Advanced organic chemistry: reactions, mechanisms, and structure (4th ed.). New York: Wiley. ISBN 978-0-471-60180-7.
- ^ a b "Aromaticity. Benzene and Other Aromatic Compounds". Virtual Textbook of Organic Chemistry. Michigan State University.
- ^ "phenyl". English by Lexico Dictionaries. Archived from the original on February 16, 2013. Retrieved 24 July 2019.
- ^ McMurry, John E. (2009). Organic Chemistry, Enhanced Edition. Cengage Learning. p. 518. ISBN 9781111790042.
- ^ Hansch, Corwin.; Leo, A.; Taft, R. W. (1991-03-01). "A survey of Hammett substituent constants and resonance and field parameters". Chemical Reviews. 91 (2): 165–195. doi:10.1021/cr00002a004. ISSN 0009-2665.
- ^ Hameka, Hendrik F. (1987). "Computation of the structures of the phenyl and benzyl radicals with the UHF method". The Journal of Organic Chemistry. 52 (22): 5025–5026. doi:10.1021/jo00231a035. ISSN 0022-3263.
- ^ Silva, Pedro Jorge (2009). "Inductive and Resonance Effects on the Acidities of Phenol, Enols, and Carbonyl
α -Hydrogens". The Journal of Organic Chemistry. 74 (2): 914–916. doi:10.1021/jo8018736. hdl:10284/3294. ISSN 0022-3263. PMID 19053615.
External links
edit- Media related to Phenyl group at Wikimedia Commons