Introduction to Halogenoalkanes (A-Level Chemistry)

Key Terms

• Polar bond: Asymmetrical distribution of electrons in a bond due to differences in electronegativity.
• Nucleophile: Atom or compound with a negative charge that donates electrons to form a bond.
• Electrophile: Atom or compound with a positive charge that accepts electrons to form a bond.

Features of Halogenoalkanes

• Alkanes with one or more hydrogen atoms replaced by halogen atoms.
• C-Halogen Bond:
  • Polar due to higher electronegativity of halogens compared to carbon.
  • Creates a dipole-dipole interaction.
  • Carbon is open to nucleophilic attacks.

Types of Halogenoalkanes

• Primary: Carbon bonded to one alkyl group.
• Secondary: Carbon bonded to two alkyl groups.
• Tertiary: Carbon bonded to three alkyl groups.

Relative Rate of Reaction of Halogenoalkanes

• Bond breaks during reactions, influenced by bond polarity and enthalpy.

Trends in Bond Polarity

• Halogen size increases down the group, increasing bond length.
• C-F bond is most polar; C-I is least polar.

Trends in Bond Enthalpy

• Bond length increases as halogen size increases, decreasing bond enthalpy.
• C-F bond is strongest, C-I bond is weakest.

Investigating Reactivity

• Experiment steps:
  1. Dissolve halogenoalkane in ethanol.
  2. Add dilute nitric acid and silver nitrate.
  3. Add NaOH or KOH, observe precipitate formation.
• Results suggest iodoalkanes are most reactive, supporting bond strength as a key factor.

Comparing Primary, Secondary, and Tertiary Halogenoalkanes

• Tertiary react fastest, followed by secondary, then primary.

Importance in A-Level Chemistry

• Fundamental in organic chemistry, serving as an introduction to organic reactions.
• Important for understanding synthesis and properties of more complex organic compounds.

Properties

• Higher boiling points than alkanes.
• Polar, more soluble in water.
• Higher reactivity, used as precursors in synthesis.

Synthesis

• Halogenation: Replacing hydrogen in alkanes with halogen atoms.
• Methods include free-radical substitution and nucleophilic substitution.

Applications

• Used as solvents, refrigerants, and in pharmaceuticals.

These notes provide an overview of the introduction to halogenoalkanes, covering their features, types, reactivity, and importance in A-Level Chemistry.