Phenyl 

The word “Phenyl” is a derivative from a French word phényl, which in turn was a derivative from the Greek word phaino, meaning ‘shining,’ since the first phenyl compounds named were the by-products of the production and the refining of various gases used for lighting. According to the scientist McMurry, “The word is derived from the Greek word pheno (“I bear light”), which commemorates the discovery of benzene from the oily residue left by the gas used in street lamps in the London by Michael Faraday in 1825.”

What is Phenyl?

In organic chemistry, a cyclic group of atoms with the formula \({C_6H_5}\) is known as the phenyl group or the phenyl ring.

Phenyl groups are closely related to benzene and can also be known as a benzene ring, except minus a hydrogen, which is substitutable by another element or compounds that can serve as a functional group.

Phenyl groups have six carbon atoms bound together in a hexagonal planar ring, five of which are binding to individual hydrogen atoms. The remaining carbon is attached to a substitute. Phenyl groups are common in organic chemistry. Although often depicted with varying double and single bonds, phenyl groups are chemically aromatic and have equal bond lengths between carbon atoms in the ring.

Nomenclature

Typically, the “phenyl group” is synonymous with C₆H₅− and is represented by Ph or, archaically as the symbol \({\phi}\). Often, benzene is known as PhH. Generally, phenyl groups are bound to other atoms or groups. For example, triphenylmethane \({Ph_3CH}\) has three phenyl groups attached to the same carbon centre. Many or even most of the  phenyl compounds are often not referred with the term “phenyl.” For instance, the chloro-derived \({C_6H_5Cl}\) is generally known as chlorobenzene, but it may be called phenyl chloride. In particular (and rare) cases, isolated phenyl groups are detected: the phenyl anion \({C_6H_5-}\), the phenyl cation \({C_6H_5+}\) and the phenyl radical \({C_6H_5}{^\cdot}\).

While Ph and phenyl uniquely denote \({C_6H_5}\), substituted derivatives are often using phenyl terminologies. \({O_2NC_6H_4}\), for example, is nitrophenyl and \({F_5C_6}\) is pentafluorophenyl. The monosubstituted phenyl groups (i.e., disubstituted benzenes) are associated with electrophilic aromatic substitution reactions, and the products adopt the same arene substitution pattern.

The substituted phenyl compound thus comprises three isomers: ortho (1,2-disubstitution), meta (1,3-disubstitution) and para (1,4-disubstitution). For instance, a disubstituted phenyl compound (tri-substituted benzene) can either be 1,3,5-trisubstituted or 1,2,3-trisubstituted. Higher levels of substitution of which the pentafluorophenyl group is an example that exists and are given the names as per the IUPAC nomenclature.

Characteristics of the Phenyl Group

• It is also known as the phenyl radical.
• The formula of the phenyl group is; \({C_6H_5}\)
• Its density is; 1.248 g/mL at \({25 \degree C}\)
• The Molecular Weight/ Molar Mass is; 77.106 g/mol.
• The boiling point of the phenyl group is \({232.2\pm}{7.0 \degree C}\) at 760 mmHg.
• Also, the melting point is \({- 30 \degree C}\).
• The chemical formula of the phenyl group is \({C_6H_5}\).

Structure, Bonding, and Characterization

Structure

Phenyl compounds are known as extracts of the benzene \({C_6H_6}\). The phenyl group is related to the vinyl group in terms of its electronic properties. The higher electronegativity of its \({sp^2}\) carbon atoms and due to the ability of its \({\pi}\) system to donate an electron density when conjugation is necessary as a resonance donation group(+M), it is known as an inductively withdrawing group (-I). A phenyl is a hydrophobic group. Phenyl groups sometimes resist oxidation and reduction. Phenyl groups (like all aromatic compounds) have elevated stability relative to equivalent bonding in aliphatic (non-aromatic) groups. This improved stability is due to the unique characteristics of aromatic molecular orbitals.

Bonding

The bond length between the carbon atoms in the phenyl group is approximately \(1.4 {\AA}\).

Characterization

In \({^1H-NMR}\) spectroscopy, protons in the phenyl group usually have chemical shifts of around 7.27 ppm. The aromatic ring current is the reason behind these chemical shifts and can differ depending on the substituent.

Preparation of Phenyl

Reagents that serve as sources of the phenyl anion or phenyl cation, usually introduce phenyl groups. Representative reagents include phenyl lithium (C₆H₅Li) and phenylmagnesium bromide (C₆H₅MgBr). Electrophiles attack benzene to produce phenyl derivatives:

\({C_6H_6 + E^+ \longrightarrow C_6H_5E + H^+}\)

Where \({E^+} (‘electrophile’) = {Cl^+}, {NO_2^+}, {SO_3}\). These reactions are electrophilic aromatic substitutions.

Representative Compounds Containing Phenyl Groups

• Atorvastatin (Lipitor): is a leading drug that contains two phenyls and one p-fluorophenyl group. It is useful in reducing cholesterol levels in people with hypercholesterolaemia.
• Fexofenadine (Allegra, Telfast): is another blockbuster drug containing both the diphenylmethyl group and the p-phenylene \({C_6H_4}\) group. It’s an antihistamine used to treat allergies.
• Phenylalanine: is a common amino acid. It is useful as an additional nutritional supplement in foods and drinks because of its reputed analgesic and antidepressant effects.
• Biphenyl: consists of two phenyl groups. The two rings tend not to be coplanar. Biphenyl is mainly useful as a heat transfer agent as a combination of diphenyl ether.
• Chlorobenzene (or phenyl chloride): is a solvent. It plays as an intermediate in the production of commodities such as herbicides, dyestuffs, and rubber.

Phenyl groups are present in many organic compounds, both natural and synthetic. The amino acid phenylalanine, which contains a phenyl group, is the most abundant among natural products. There are many drugs as well as many pollutants that have phenyl rings. Phenol \({C_6H_5OH}\) is one of the simplest phenyl-containing compounds.

Chemical Properties

The phenyl group, when phenol reacts with bromine solution, forms bromine substituted phenol and hydrogen bromide. The chemical equation is:

\({2C_6H_5OH + 5Br_2 \longrightarrow 2C_6H_2Br_2OH + 6HBr}\)

Uses

• Today it’s useful in combination with other phenols in several institutional and domestic disinfectant formulations.
• Helps in removing the odour and encouraging sanitation.
• Useful as a disinfectant in public places such as schools, hotels, markets and offices.
• It exhibits pharmacological properties and is useful as an antioxidant, analgesic, choleretic, etc.

FAQs about Phenyl 

Q.1. Are phenyl and phenol same?

Ans. Phenyl and phenol are often confusing. The main difference between phenol and phenyl is that phenol is composed of an oxygen atom, whereas phenyl does not have oxygen atoms bound to it. The difference between Phenyl and Phenol: Phenyl is a benzene ring, that lacks a hydrogen atom and is an unstable compound. It is a highly reactive compound. Whereas, phenol is the simplest aromatic alcohol with the formula C₆H₅OH and is a stable compound. It’s much less reactive and has a stable chemical structure.

Q.2. How many carbon atoms does the phenyl group contain?

Ans. Phenyl groups are closely related to benzene and can also be known as a benzene ring. Phenyl groups have six carbon atoms bound together in a hexagonal planar ring, five of which are binding to individual hydrogen atoms. The remaining carbon is attached to a substitute.

Q.3. Does the phenyl group undergo oxidation or reduction process?

Ans. Phenyl groups tend to resist both reduction and oxidation. Phenyl groups (similar to all other aromatic compounds) are relatively more stable than aliphatic (non-aromatic) groups. This improved stability is due to the peculiar properties of aromatic molecular orbitals.

Q.4. Comment on the occurrence of the phenyl group.

Ans. Phenyl groups are present in many organic compounds, both natural and synthetic. The amino acid phenylalanine, which contains a phenyl group, is the most abundant among natural products. There are many drugs as well as many pollutants that have phenyl rings. Phenol \({C_6H_5OH}\) is one of the simplest phenyl-containing compounds. A main petrochemical industry commodity is the “BTX” composed of benzene, toluene and xylene, are all building blocks for phenyl compounds.