Reactions of Aromatic Compounds

Reactions of Aromatic Compounds

Introduction to Aromatic Compounds

  • Aromatic compounds are a class of chemical substances containing a planar ring of atoms usually linked by delocalised pi electrons.
  • Benzene is an important example of an aromatic compound, represented by the formula C6H6.

Structure and Stability of Aromatic Compounds

  • The hexagonal structure of benzene with alternating single and double bonds contributes to its stability.
  • It is more stable than predicted due to delocalisation of pi electrons above and below the plane of the carbon atoms, known as resonance.
  • This extra stability is referred to as aromatic stabilisation.

Reactions of Aromatic Compounds

  • Aromatic compounds do not often undergo addition reactions, due to such reactions breaking the delocalised electron system and thus removing their aromatic character.
  • Instead, they usually undergo substitution reactions that preserve the delocalised system.
  • The most common form of these reactions is Electrophilic Aromatic Substitution (EAS).

Electrophilic Aromatic Substitution

  • In EAS, an electrophile is attracted to the electron-rich benzene ring, causing the ring to act as a nucleophile.
  • The electrophile replaces one hydrogen atom on the ring without disrupting the delocalised electron system.
  • Common examples of EAS include nitration, sulphonation, halogenation, Friedel-Crafts alkylation and Friedel-Crafts acylation.

Colour in Chemistry

  • Aromatic compounds are often involved in producing colour due to their conjugated systems absorbing light in the visible spectrum.
  • The conjugated system allows for the movement of electrons across multiple atoms, and this movement can absorb light, often resulting in a characteristic colour.
  • Understanding the correlation between the structure of aromatic compounds and the colour they produce is important in industries such as dye and pigment production, in addition to analytical chemistry systems like UV-Visible spectrometry.

Safety and Environmental Impact

  • Aromatic compounds, especially those that are synthetically produced, can have detrimental effects on both human health and the environment.
  • Many aromatic compounds are volatile and can release toxic fumes or contribute to air pollution when not handled responsibly.
  • Careful management and regulation are imperative for producing, using, and disposing of these compounds safely.