Organic Chemistry 2 - Lecture 5: Aromatic Chemistry Part 2

Overview

• Focus on aromatic electrophilic substitution reactions.
• Exploration of phenols and anilines.
• Ranking nucleophilicity of substituted benzenes.

Key Topics

Aromatic Compounds Overview

• Benzene: Stable, reacts with strong electrophiles.

Types of Benzene Derivatives

• Phenol: Hydroxybenzene, acts as an acid.

  • Can lose a proton, forming a phenoxide ion.
  • More acidic than normal alcohol due to electron delocalization.
  • pKa around 10, showing higher acidity.
  • Resonance stabilization aids in its acidity.

• Aniline: Aminobenzene, acts as a base.

  • Can grab a proton, making it less basic than alkyl amines.
  • Lone pair in resonance with the ring, reduces availability to attack protons.

Phenols

• Acts as acids, losing the proton to form phenoxide in basic conditions.
• Phenoxide is more stable due to resonance stabilization.
• Greater electron density makes them more reactive than benzene.

Anilines

• Less basic due to delocalization of nitrogen lone pair.
• Cannot be used in reactions with acidic environments as it forms anilinium cation, which is unreactive.

Nucleophilicity Ranking

• Phenoxide: Most nucleophilic due to high electron density.
• Aniline: Next in nucleophilicity.
• Phenol: Less nucleophilic than aniline.
• Benzene: Baseline reference for nucleophilicity.
• Aniline in Acidic Conditions: Least nucleophilic due to forming an unreactive cation.

Key Takeaways

• Phenols and anilines are more reactive than benzene in electrophilic aromatic substitution.
• Nucleophilicity influenced by electron density and ability to participate in resonance.
• Avoid acidic environments with aniline to prevent deactivation.

Conclusion

• Review: Understanding of aromatic electrophilic substitution, phenols, and anilines.
• Next Steps: Familiarity with electrophile generation and step-wise reaction processes essential.

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This concludes Lecture 5 and Topic 3 in the course.