Lecture Notes on Haloalkanes

Introduction

• Objective: Describe the structure and physical properties of haloalkanes.
• Alternative Name: Halogenoalkanes.
• General Structure: Contains a halogen atom bonded to an alkane.

Naming Haloalkanes

• Prefix: Halogen as prefix followed by parent alkane.
• Position Indication: Numbers indicate positions of functional groups (e.g., halogen).
• Formula: General formula is CnH2n+1X, where X is the halogen.
• Multiple Halogens: e.g., 1,2-dichloroethane, 1,2,3-tribromo propane.
• Different Halogens: Listed alphabetically, not by position number.

Classification of Haloalkanes

• Primary Haloalkanes: Halogen bonded to a carbon atom attached to one other carbon.
• Secondary Haloalkanes: Halogen bonded to a carbon atom attached to two other carbons.
• Tertiary Haloalkanes: Halogen bonded to a carbon atom attached to three other carbons.

Bond Polarity

• Carbon-Halogen Bond: Polar due to halogen electronegativity.
• Charge Distribution: Halogen has a slight negative charge; carbon has a slight positive charge.

Physical Properties of Haloalkanes

• Boiling Points:
  • Higher than equivalent alkanes due to intermolecular forces.
  • Alkanes: Nonpolar, with London forces (weak, low boiling points).
  • Haloalkanes:
    • London forces plus permanent dipole-dipole interactions (stronger, higher boiling points).
    • Boiling point increases down group 7 due to increasing electron count in halogens, enhancing London forces.

Solubility

• Insoluble in Water: Cannot form hydrogen bonds.
• Soluble in Non-polar Solvents: e.g., cyclohexane.

Conclusion

• Able to describe the structure and physical properties of haloalkanes.