Chemical Reactions of Benzene: Electrophilic Substitution (Hand Written Notes)
Master the fundamental Chemical Reactions of Benzene with these comprehensive handwritten notes, specifically designed for B.Pharm 3rd Semester Organic Chemistry 2 students. Focus on the core concept of Electrophilic Substitution Reactions and their mechanisms.
Key Reactions Covered:
- Detailed explanation of Electrophilic Aromatic Substitution reactions.
- Nitration: Introduction of a nitro group to the benzene ring.
- Sulphonation: Formation of benzenesulfonic acid.
- Friedel-Crafts Alkylation: Adding alkyl groups to benzene.
- Friedel-Crafts Acylation: Introducing acyl groups to benzene.
- Halogenation: Substitution of hydrogen with halogens.
These notes provide clear, step-by-step mechanisms essential for understanding benzene's reactivity. Download this free PDF to enhance your exam preparation and deepen your knowledge of aromatic chemistry.
Keywords:
Benzene Reactions PDF, Electrophilic Substitution Mechanism, Nitration of Benzene, Sulphonation of Benzene, Friedel-Crafts Alkylation Benzene, Friedel-Crafts Acylation Benzene, Halogenation of Benzene, Organic Chemistry 2 Notes, B.Pharm 3rd Sem Chemistry, Aromatic Compounds Notes, Free Chemistry Notes, Handwritten Chemistry Notes, DuloMix Slides.
The Reactivity of Benzene: A Deep Dive into Electrophilic Aromatic Substitution
Benzene, the quintessential aromatic compound, holds a unique place in organic chemistry. Its exceptional stability, stemming from its delocalized pi electron system, dictates its reactivity. Unlike alkenes, which undergo addition reactions, benzene primarily undergoes electrophilic aromatic substitution (EAS) reactions. These reactions are fundamental for functionalizing the benzene ring and are a crucial topic for B.Pharm 3rd-semester students in Organic Chemistry 2. Our meticulously prepared handwritten notes provide a clear and comprehensive guide to the key EAS reactions of benzene, complete with mechanisms.
Understanding Electrophilic Aromatic Substitution (EAS)
EAS reactions involve the substitution of a hydrogen atom on the aromatic ring by an electrophile (an electron-deficient species). The aromaticity of the ring is temporarily disrupted during the attack by the electrophile, forming a resonance-stabilized sigma complex (also known as a arenium ion or Wheland intermediate). The aromaticity is then restored by the rapid loss of a proton from the carbon bearing both the electrophile and the original hydrogen, rather than by addition across a double bond. This preservation of aromaticity is what distinguishes benzene's reactivity from that of typical alkenes.
Key Electrophilic Substitution Reactions of Benzene:
- Nitration:
This reaction introduces a nitro group (-NO₂) onto the benzene ring. It typically involves treating benzene with a mixture of concentrated nitric acid (HNO₃) and concentrated sulfuric acid (H₂SO₄). The sulfuric acid acts as a catalyst, protonating nitric acid to generate the highly reactive electrophile, the nitronium ion (NO₂⁺).
- Sulphonation:
In sulfonation, a sulfonic acid group (-SO₃H) is attached to the benzene ring. This is achieved by reacting benzene with fuming sulfuric acid (H₂SO₄ + SO₃) or concentrated sulfuric acid. The electrophile is sulfur trioxide (SO₃), which can be formed from sulfuric acid.
- Friedel-Crafts Alkylation:
This reaction introduces an alkyl group (-R) to the benzene ring. It involves the reaction of benzene with an alkyl halide (R-X) in the presence of a Lewis acid catalyst, such as aluminum chloride (AlCl₃). The electrophile is an alkyl carbocation (R⁺) or a polarized R-X/Lewis acid complex.
- Friedel-Crafts Acylation:
This reaction introduces an acyl group (-COR) to the benzene ring, forming a ketone. It uses an acyl halide (R-CO-X) or acid anhydride in the presence of a Lewis acid catalyst (AlCl₃). The electrophile is a highly reactive acylium ion (R-C≡O⁺).
- Halogenation:
Benzene can be halogenated (e.g., chlorinated or brominated) by reacting it with a halogen molecule (Cl₂ or Br₂) in the presence of a Lewis acid catalyst, such as iron(III) halide (FeCl₃ or FeBr₃). The Lewis acid activates the halogen, forming a stronger electrophile (e.g., Br⁺ or Cl⁺ equivalent) that can attack the benzene ring.
Why These Handwritten Notes are a Must-Have:
For B.Pharm students, a clear understanding of these reactions is vital for comprehending drug synthesis pathways and the reactivity of aromatic rings in medicinal chemistry. Our notes provide:
- Clear Mechanism Flow: Step-by-step visual guidance through electrophile generation, attack, and deprotonation.
- Reagent Identification: Easy to remember the specific reagents and catalysts required for each reaction.
- Conceptual Reinforcement: Helps solidify the concept of aromaticity preservation during substitution.
Download this free PDF today to reinforce your understanding of benzene's chemical reactivity, prepare effectively for your Organic Chemistry 2 exams, and build a strong foundation for advanced topics in pharmaceutical sciences.
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