Hello Alkane and Hello Arene

Introduction

• When a halogen (such as chlorine, bromine, iodine) replaces hydrogen in an alkane or arene, it forms haloalkane or haloarene.
• Halogen means an element that comes in the 17th group of the periodic table.
• Haloalkane = Halogen + Alkane (Example: Methyl chloride)
• Haloarene = Halogen + Aromatic Hydrocarbon (Example: Benzyl chloride)

Structure of Haloalkane

• The structure of hydrocarbon in which one or more hydrogen atoms are replaced by a halogen.
• Common example: CH3Cl (Methyl chloride)

Haloarene

• Hydrocarbon with an aromatic ring and a halogen attached.
• Common example: Benzyl chloride

Nomenclature

• According to IUPAC rules:
  • Find the longest carbon chain.
  • Number the chain from the end nearest to the halogen.
• Examples:
  • 1-Chloropropane
  • 2-Bromopropane

Uses of Haloalkane and Haloarene

• Haloalkanes and haloarenes are used in pharmacy, anesthesia, and other industries.
• Used as solvents, disinfectants, etc.

Hybridization

• Carbon mainly undergoes SP3 and SP2 hybridization.
• SP3 hybridization: One s and three p orbitals combine to form four sigma bonds.
• SP2 hybridization: One s and two p orbitals combine to form three sigma and one pi bond.
• Haloalkane mostly exhibits SP3 while haloarene shows SP2 hybridization.

Reactions and Preparation

Free Radical Substitution

• Free radical halogenation reaction especially occurs between alkanes and chlorine or bromine in the presence of electricity or UV light.
• Example: CH4 + Cl2 → CH3Cl + HCl

Free Radical Mechanism

• Free radicals are generated and react with alkanes.
• Initiation: Cl2 → 2Cl•
• Propagation: CH4 + Cl• → CH3• + HCl
• Termination: Cl• + Cl• → Cl2

Addition Mechanism

• When an alkene reacts with hydrogen chloride or bromine, it follows Markovnikov's rule.
• Example: Propene + HCl → 2-Chloropropane
• Important: Markovnikov's rule: The negative part attaches to the carbon atom having fewer hydrogen atoms.

Reactions with Alcohol

• Alcohol + PX3 → RX + POX3
• Example: R-OH + PCl5 → R-Cl + POCl3

Removal of Halogen from Alkyl Halide

• To remove halogen from alkyl halide, it reacts with sodium iodide in acetone.
• Example: R-Cl + NaI → R-I + NaCl

Formation of Arene from Halogen

• Free radical electrophilic substitution.
• Arene + Cl2/FeCl3 → Haloarene

Physical Properties

• Melting Point and Boiling Point
  • Higher than hydrocarbons.
  • More branching = Lower boiling point.
• Density
  • Bromine and iodine derivatives have higher density.
• Solubility
  • Soluble in polar solvents.
  • dissolves well in non-polar solvents.

Uses and Importance

• In pharmaceuticals, agriculture, and industrial applications.
• Used in everyday products: Chlorine disinfectants, iodine thyroxine hormone, etc.
• In anesthetics: Haloform, chloroform.