Friedel-Crafts Acylation & Alkylation: Hand Written Notes (B.Pharm 3rd Sem O.Chem 2)
Gain a comprehensive understanding of Friedel-Crafts Acylation and Alkylation with these detailed handwritten notes. Tailored for B.Pharm 3rd Semester Organic Chemistry 2 students, this resource covers both reactions thoroughly.
Topics Included:
- Friedel-Crafts Acylation (AlCl₃): Definition, detailed mechanism, and practical applications.
- Friedel-Crafts Alkylation (AlCl₃): Definition, step-by-step mechanism, and synthetic uses.
- Critical discussion on the Limitations of both Friedel-Crafts Acylation and Alkylation reactions.
These notes are essential for mastering electrophilic aromatic substitution reactions, providing clear explanations and visual aids. Download this free PDF to excel in your organic chemistry studies.
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Mastering Aromatic Substitution: A Deep Dive into Friedel-Crafts Acylation and Alkylation
The Friedel-Crafts reactions, encompassing both alkylation and acylation, are among the most fundamental and versatile tools in organic synthesis for the functionalization of aromatic compounds. For B.Pharm 3rd-semester students delving into Organic Chemistry 2, a thorough understanding of these electrophilic aromatic substitution reactions, their mechanisms, and limitations is paramount. Our comprehensive handwritten notes provide a clear, step-by-step guide to both reactions, making complex concepts accessible and aiding in effective learning.
Friedel-Crafts Alkylation: Extending Carbon Chains
Friedel-Crafts Alkylation involves the electrophilic substitution of an alkyl group onto an aromatic ring, typically using an alkyl halide (R-X) and a Lewis acid catalyst like aluminum chloride (AlCl₃).
Mechanism:
The reaction proceeds via the generation of a carbocation (R⁺) from the alkyl halide and the Lewis acid. This carbocation then acts as an electrophile, attacking the electron-rich aromatic ring. The subsequent deprotonation regenerates the aromaticity and forms the alkylated product.
Limitations:
- Polyalkylation: The newly introduced alkyl group is activating towards further electrophilic substitution, making the product more reactive than the starting material. This often leads to over-alkylation, forming multiple alkyl groups on the ring.
- Carbocation Rearrangements: Carbocations formed during the reaction can undergo rearrangements (e.g., hydride or alkyl shifts) to form more stable carbocations. This results in mixtures of products, where the desired alkyl group might not be the primary one.
- Deactivating Groups: Aromatic rings already bearing electron-withdrawing (deactivating) groups (e.g., -NO₂, -COOH, -SO₃H) do not undergo Friedel-Crafts alkylation.
- Vinylic/Arylic Halides: Vinylic and arylic halides cannot be used as they do not form stable carbocations.
Friedel-Crafts Acylation: Introducing Acyl Groups
Friedel-Crafts Acylation involves the electrophilic substitution of an acyl group (R-CO-) onto an aromatic ring, typically using an acyl halide (R-CO-X) or an acid anhydride and a Lewis acid catalyst (AlCl₃).
Mechanism:
The key electrophile in acylation is the acylium ion (R-C≡O⁺), which is generated by the reaction of the acyl halide or anhydride with the Lewis acid. This highly stabilized cation attacks the aromatic ring, followed by deprotonation and proton loss to restore aromaticity, yielding an aryl ketone.
Limitations:
- No Polyacylation: Unlike alkylation, acylation stops after the introduction of one acyl group. This is because the carbonyl group of the ketone is an electron-withdrawing (deactivating) group, making the product less reactive than the starting material towards further electrophilic attack. This is a significant advantage over alkylation.
- Deactivating Groups: Similar to alkylation, aromatic rings with strong deactivating groups (e.g., -NO₂, -SO₃H) are unreactive towards Friedel-Crafts acylation.
- Lewis Acid Stoichiometry: A stoichiometric amount or more of the Lewis acid (AlCl₃) is often required because it forms a stable complex with the ketone product, effectively removing it from the reaction equilibrium.
Why These Notes Are Essential for B.Pharm Students:
These handwritten notes simplify the complex mechanisms of Friedel-Crafts reactions. For pharmaceutical students, understanding how to functionalize aromatic rings is critical for drug synthesis and medicinal chemistry. The notes offer:
- Clear Mechanism Diagrams: Visual representation of electron flow and intermediate formation.
- Highlighting Key Differences: Clearly distinguishes between the advantages and disadvantages of alkylation vs. acylation.
- Exam-Oriented Content: Focuses on concepts frequently tested in examinations for Organic Chemistry 2.
Download this free PDF to gain a profound understanding of Friedel-Crafts Acylation and Alkylation, ensuring you are well-prepared for your studies and future pharmaceutical endeavors.
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