EF

Ochem lecture 14

Lecture Information

  • Course: Chemistry 2420

  • Lecture: 14

  • Date: February 24th, 2025

  • Instructor: Amani A. Abdelghani

  • Email: aabdelghani@upei.ca

Chapter Overview

  • Chapter 18: Reactions of Benzene and Substituted Benzenes

    • 18.1: The Nomenclature of Monosubstituted Benzenes

    • 18.2: The General Mechanism for Electrophilic Aromatic Substitution Reactions

    • 18.11: The Nomenclature of Disubstituted and Polysubstituted Benzenes

    • 18.3-18.7: The General Mechanism for Electrophilic Aromatic Substitution Reactions

    • 18.8: Alkylation of Benzene by Acylation–Reduction

    • 18.22: The Synthesis of Cyclic Compounds

18.1 The Nomenclature of Monosubstituted Benzenes

  • Naming Aromatics

    • Monosubstituted benzenes are named as "substituents" of benzene.

    • Common examples:

      • Br: bromobenzene

      • Cl: chlorobenzene

      • NO2: nitrobenzene

      • CH2CH3: ethylbenzene

  • Special Names:

    • Classic names must be memorized.

      • Toluene (C6H5-CH3)

      • Benzaldehyde (C6H5-CHO)

      • Phenol (C6H5-OH)

      • Aniline (C6H5-NH2)

      • Benzoic Acid (C6H5-COOH)

      • Benzonitrile (C6H5-CN)

Other Terminology

  • Terms to Know:

    • Phenyl chloride: C6H5-Cl

    • Diphenyl ether: C6H5-O-C6H5

    • Aryl group: (Ar)

    • Benzyl chloride: C6H5-CH2-Cl

    • Benzyl alcohol: C6H5-CH2-OH

    • Benzylic Carbon: carbon connected to the benzyl group

18.2 The Nomenclature of Disubstituted and Polysubstituted Benzenes

  • Position Indication:

    • Substituents may be positioned via numbering or using ortho (o), meta (m), para (p) prefixes.

      1. Ortho: adjacent substituents

      2. Meta: one carbon apart

      3. Para: opposite substituents

  • Naming Guidelines:

    • If substituents differ, the one with higher priority is position #1.

    • Number in direction for lowest substituent number.

    • Alphabetical order if no priority.

  • Examples:

    • 2-Methylaniline (ortho-methylaniline)

    • 2-Ethylbenzoic acid (o-ethylbenzoic acid)

    • 1-Chloro-3-iodobenzene (m-chloroiodobenzene)

    • 1-Bromo-3-nitrobenzene (m-bromonitrobenzene)

    • 4-Aminophenol (p-aminophenol)

    • 1-Fluoro-4-methylbenzene (p-fluorotoluene)

18.3 - 18.7 General Mechanism for Electrophilic Aromatic Substitution Reactions

Electrophilic Aromatic Substitution Mechanism

  • Benzene is less reactive compared to alkenes due to stability and does not react with weak electrophiles (HBr, Br2).

  • Requires strong electrophiles (E+).

Types of Electrophiles (E+)

  1. Nitration of Benzene:

    • Uses nitric acid and sulfuric acid as catalysts.

  2. Sulfonation of Benzene:

    • Uses concentrated or fuming sulfuric acid.

  3. Bromination and Chlorination:

    • Requires Lewis acid catalysts (like FeBr3 or FeCl3).

  4. Friedel–Crafts Acylation:

    • Acyl group introduced via acyl chloride or acid anhydride.

  5. Friedel–Crafts Alkylation:

    • An alkyl group substitutes a hydrogen atom.

  • Complications arise from carbocation rearrangements.

18.8 Alkylation of Benzene by Acylation-Reduction

  • Process: Acylation followed by reduction of the carbonyl group.

  • Two reduction methods:

    1. Clemmensen Reduction:

      • Uses zinc amalgam in acidic conditions.

    2. Wolff-Kishner Reduction:

      • Uses hydrazine (N2H4) under alkaline conditions.

Summary of Electrophilic Reactions

  • Types of E+ and Products:

    1. Nitration: Ar-NO2

    2. Sulfonation: Ar-SO3H

    3. Bromination: Ar-Br

    4. Chlorination: Ar-Cl

    5. Friedel-Crafts Acylation: Ar-C-R

18.22 The Synthesis of Cyclic Compounds

  • Cyclic Compound Formation:

    • Intramolecular reactions favor producing five- or six-membered rings.

Conclusion

  • End of Lecture 14:

    • "Chemistry is awesome!"

    • Topics of interest: Chocolate, Caffeine (Theobromine), Alcohol (Ethanol), Happiness (Serotonin), Love (Dopamine), Adrenaline.