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.