Phenyl group

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In organic chemistry, the phenyl group or phenyl ring has the formula C6H5. The six carbon atoms are arranged in a planar ring, each of which is bonded to an H atom. Phenyl groups are pervasive in organic chemistry.[1]

Contents

Nomenclature

Phenyl groups are often abbreviated as Ph or Φ (which is archaic). Benzene is sometimes denoted as PhH. Phenyl groups are attached to other atoms in a molecule. For example, triphenylmethane (Ph3CH). Phenyl compounds are so common that they often have multiple names, some of which do not use the term "phenyl." For example the chlorine derivative 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 (C6H5-), the phenyl cation (C6H5+), and the phenyl free radical (C6H5).

Although Ph and phenyl uniquely denote C6H5, substituted derivatives also are described using the phenyl terminology. For example, O2NC6H4 is nitrophenyl (of which three isomers are possible) and F5C6 is pentafluorophenyl.

Structure, bonding, characterization

Phenyl 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. The phenyl group is hydrophobic. Phenyl groups tend to resist oxidation and reduction, so they are highly-stable substituents.

In 1H-NMR spectroscopy, protons of a phenyl group typically absorb chemical shifts around 7.27 ppm. The position of these chemical shifts is influenced by aromatic ring current, and these values 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 (C6H5Li) and phenylmagnesium bromide (C6H5MgBr). Electrophiles attack benzene to give phenyl derivatives:

where E+ (the "electrophile") = Cl+, NO2+, SO3H+. These reactions are called electrophilic aromatic substitutions.

Lipitor, a blockbuster drug featuring two phenyl and one p-fluorophenyl groups.

Allegra, another blockbuster drug, which features a diphenylmethyl group as well as a p-phenylene (C6H4) group.

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