What is an aryl group in chemistry

In organic chemistry, an aryl group is a substituent group derived from an aromatic ring . In other words, it represents those substituents that contain rings of benzene (or its derivatives), naphthalene (or its derivatives) or other aromatic rings linked directly to the main chain of an organic compound. Some common examples of aryl groups are phenyl (which comes from benzene), alpha and beta naphthyl (both from naphthalene).

When a particular aryl group is not needed or desired in a molecule, then it is usually represented generically by the symbol –Ar. This is equivalent to the way alkyl radicals are generically represented by the symbol –R.

From a structural point of view, an aryl group is what is obtained when a hydrogen is subtracted from an aromatic compound (also called arene) , thus becoming a radical.

Aryl group nomenclature

The simplest aryl group is the one that comes from benzene. This is called the phenyl group. Care must be taken not to confuse it with the benzyl group, which, despite containing a benzene ring, is not an aryl, since the hydrogen it loses was not bonded to the ring but to a methyl group.

Aryl groups derived from phenyl are named following the common rules of systematic nomenclature, but taking as carbon 1 the carbon that is attached directly to the main chain.

Example:

2,3-Dichlorophenyl is an aryl group that has chlorine atoms attached to the ring next to the point of attachment to the main chain.

In the case of other aromatic compounds, such as those with polycyclic systems (such as naphthalene, anthracene, phenanthrene, etc.), the aryl radical is named by preceding the locant of the carbon that is attached to the main chain and substituting the ending of the parent compound with the suffix -yl. If it has substituents, these are named first along with their respective locants, as usual.

Example:

2-Methyl-1-naphthyl is an aryl group formed by a naphthalene molecule attached to the main chain through carbon 1 and possessing a methyl group on carbon 2.

Finally, there are some aromatic compounds that have common names such as toluene, xylene. In these cases, the same name is used as the root and the ending is changed to ilo.

Characteristics of aryl groups

• They have planar cycles with double bonds and, in some cases, conjugated lone pairs of electrons.
• They comply with Hückel’s rule of aromaticity, which means that they have a total of 4n+2 (2, 6, 10, etc.) electrons delocalized by resonance.
• Aryl groups can act as electron density donors by resonance effect.

Examples of aryl groups

Any aromatic compound can be converted to an aryl group by losing a hydrogen. Here are some examples of very common aryl groups, from the simplest to the most complex:

Phenyl group (C ₆ H ₅ )

The isomers of methylphenyl, also known as tolyl (C ₆ H ₅ CH ₃ )

alpha and beta naphthyl

2-methyl-α-naphthyl and 1-methyl-α-naphthyl