Aromaticity in Organic Chemistry

Aromaticity has been deeply rooted in chemical literature, even before the structural and bonding principles have been clearly established. Historically, the molecule benzene is closely associated with aromaticity. The first use of the word aromatic as a chemical term was done by Hofmann in 1855. The term aromaticity owes its name to the pleasant aroma that some members of this class have and later on it was denoting exceptional stability that this family of compounds exhibit.

Aromaticity has been one of the most ubiquitous concepts in chemical literature. Before exploring aromatic compounds, let’s first discuss what is a compound? A compound is a substance that is formed when two or more elements react together. A chemical compound is normally thought of as having a definite, fixed composition and a simple, rational formula, which expresses the compiling ratios of the component atoms, i.e. its stoichiometry.

Why do Aromatic Compounds Smell?

During the nineteenth century, a large number of organic compounds were isolated from balsams, resins and oils. These organic compounds were classified as aromatic because all of them had a characteristic smell.  Aromatic compounds such as benzene are more stable than suggested from their structure. They undergo reactions which retain the aromatic ring system, and behave differently from alkenes or polyenes.

Smell and taste are chemical senses that sample the molecular composition of food and environment.  Aromatic compounds, including phenolic, ketones and terpenes, create the main odors of vegetables and fruits. The aromatic hydrocarbons are used as solvents and as feedstock for many organic compounds. Benzene is the best known aromatic hydrocarbon. It is a flammable, colorless to light-yellow liquid with an aromatic odor.

Properties of Aromatic Compounds

Many aromatic compounds have a characteristic aroma and burn with a smoky flame. They are nonpolar, hydrophobic molecules which dissolve in organic solvents rather than water.

  • Aromatic molecules can interact by van der Waals interactions or with a cation through an induced dipole interaction.
  • Aromatic compounds undergo reactions where the aromatic ring is retained.
  • Electrophilic substitution and nucleophilic substitution reactions are the most common type of reaction.

Aromatic compounds are unusually stable and do not react the same way as alkenes. They prefer to undergo reactions where the stable aromatic ring is retained. The most common type of reaction for aromatic rings is electrophilic substitution but reduction reaction is also possible in aromatic compounds.