Substitution Product

Definition

A substitution product is the result of a chemical reaction where an atom or functional group in a molecule is replaced by a different atom or functional group. This is a key concept in the context of electrophilic aromatic substitution reactions, specifically the bromination of aromatic compounds.

5 Must Know Facts For Your Next Test

1. The substitution product in electrophilic aromatic bromination is the bromoaromatic compound, where a bromine atom replaces a hydrogen atom on the aromatic ring.
2. The electrophilic species involved in the bromination reaction is typically molecular bromine (Br$_2$) or a bromonium ion (Br$^+$).
3. The reaction proceeds through the formation of a Wheland intermediate, also known as a $\sigma$-complex, which is then deprotonated to give the final substitution product.
4. The position of the bromine substituent on the aromatic ring is determined by the stability of the Wheland intermediate, with the most stable position being favored.
5. Substitution products in electrophilic aromatic bromination reactions are often important intermediates in the synthesis of more complex aromatic compounds.

Review Questions

• Describe the mechanism of electrophilic aromatic substitution in the context of the bromination of benzene.
  • The mechanism of electrophilic aromatic substitution in the bromination of benzene involves the following steps: 1) The electrophilic bromine species (Br$_2$ or Br$^+$) attacks the $\pi$-system of the aromatic ring, forming a Wheland intermediate (also known as a $\sigma$-complex). 2) The Wheland intermediate is then deprotonated, resulting in the replacement of a hydrogen atom with a bromine atom on the aromatic ring, forming the substitution product, bromobenzene.
• Explain how the stability of the Wheland intermediate affects the regioselectivity of the electrophilic aromatic bromination reaction.
  • The regioselectivity of the electrophilic aromatic bromination reaction is determined by the stability of the Wheland intermediate. The most stable Wheland intermediate is formed at the position on the aromatic ring where the positive charge is best stabilized, typically through resonance stabilization. This position is then favored for the substitution of the bromine atom, leading to the formation of the most thermodynamically stable substitution product.
• Discuss the importance of substitution products in electrophilic aromatic bromination reactions for the synthesis of more complex aromatic compounds.
  • Substitution products from electrophilic aromatic bromination reactions are often key intermediates in the synthesis of more complex aromatic compounds. The bromine atom in the substitution product can undergo further functionalization, such as nucleophilic substitution, coupling reactions, or reduction, to introduce additional functional groups and build up the desired aromatic structure. This versatility makes the substitution products from electrophilic aromatic bromination an important class of compounds for organic synthesis and the preparation of a wide range of aromatic molecules.

Related terms

Electrophilic Aromatic Substitution:

A type of aromatic substitution reaction where an electrophile replaces a hydrogen atom on an aromatic ring.

Bromination:

The process of introducing a bromine atom into an organic compound, often onto an aromatic ring.

Aromatic Compound:

A cyclic, planar organic compound with a delocalized $\pi$-electron system that exhibits enhanced stability.