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Electrophilic Aromatic Substitution

Definition: What is Electrophilic Aromatic Substitution?

Electrophilic aromatic substitution is a chemical reaction in which a hydrogen atom or a functional group from an aromatic compound is substituted with another functional group, which is an electrophile [1-3].

Electrophilic Aromatic Substitution

Types of Electrophilic Aromatic Substitution

There are five different types of electrophilic aromatic substitution [2].

  1. Halogenation – replacing with chlorine (Cl) (chlorination) or bromine (Br) (bromination)
  2. Nitration – replacing with a nitrate group (NO2)
  3. Sulfonation – replacing with bisulfite (SO3H)
  4. Friedel-Crafts Alkylation – replacing with an alkyl group (R)
  5. Friedel-Crafts Acylation – replacing with an acyl group (RCO)

Examples of Electrophilic Aromatic Substitution of Benzene

Benzene can undergo electrophilic substitution reaction giving a wide range of compounds [2].

Electrophilic Aromatic Substitution Example Benzene

Examples of Electrophilic Aromatic Substitution of Other Aromatic Compounds

Aromatic compounds like phenol, aniline, naphthalene, pyrrole, furan, thiophene, pyridine, indole, and imidazole can undergo electrophilic substitution reaction. Their mechanism is similar to benzene [4-8].

Electrophilic Aromatic Substitution Examples Pyridine Phenol Pyrrole Furan Thiophene

Mechanism of Electrophilic Aromatic Substitution of Benzene [9-14]

Electrophilic Aromatic Substitution Mechanism

FAQs

Q.1. Why do aromatic compounds undergo electrophilic substitution rather than addition reactions?

Ans. Aromatic compounds like benzene undergo substitution reaction rather than addition reactions because addition reactions disrupt the delocalization of the pi molecular orbital, reducing the stability of the benzene ring. In contrast, substitution reactions only cause temporary disruption, thereby allowing the compound to retain its aromaticity.

Q.2. Why phenol undergoes electrophilic substitution more easily than benzene?

Ans. Phenol has a higher electron density than benzene, thereby making it easier for the electrophile to attack.

Q.3. Why is furan less reactive than pyrrole?

Ans. Oxygen, being more electronegative than nitrogen, distributes more negative charge density upon itself and less upon the ring, thus stabilizing the carbocation intermediate less, making furan less reactive towards EAS than pyrrole.

References

  1. Definition – Study.com
  2. Definition – Masterorganicchemistry.com
  3. Definition – Byjus.com
  4. Example – Chemistry.msu.edu
  5. Example – Byjus.com
  6. Example – Onlineorganicchemistrytutor.com
  7. Example – Chem.gla.ac.uk
  8. Example –Webpages.iust.ac.ir
  9. Mechanism – Masterorganicchemistry.com
  10. Mechanism – Byjus.com
  11. Mechanism – Cliffsnotes.com
  12. Mechanism – Chemguide.co.uk
  13. Mechanism – Chem.ucla.edu
  14. Mechanism – Chem.ucalgary.ca

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