Lecture 1, Part A: OC2 - Alkyl Halides

Lecturer: Dr. Soler

Overview

• Introduction to alkyl halides.
• Description of their structure, formation, and usefulness.
• Overview of reactions involving alkyl halides.

Organic Halogen Compounds

• Organic compounds with one or more halogens.
• Halogens denoted by 'X' combined with carbon atoms.
• Various structures include alkyl groups, carbonyls, aromatic rings.

Alkyl Halides (Halogenoalkanes)

• Subset of organic halogen compounds specifically focusing on alkyl compounds.
• Alkyl group: Carbon with an sp3 hybridized atom bound to a halogen (Cl, Br, I).
• Fluorine is ignored due to strong C-F bonds.
• Shorthand: R (alkyl group) - X (halide).
• Alkyl: functional group similar to an alkane but missing a hydrogen.
  • Examples: Methyl (methane - H), Ethyl (ethane - H), Isopropyl (isopropane - H).

Structure of Alkyl Halides

• Carbon is sp3 hybridized (tetrahedral geometry, ~109° bond angle).
• Bond between carbon and halogen involves shared electron pair.
• Structure implications:
  • Bond is polarizable.
  • Partial positive charge on alkyl side, partial negative on halogen side.

Formation of Organic Halogen Compounds

• Not covered in depth in this module.
• Methods include:
  • Hydrohalogenation: Adding HCl/HBr to alkenes or acetylenes.
  • Halogenation: Adding bromine or chlorine to alkenes or acetylenes.
  • Substitution: Replacing hydrogen in alkanes with bromine/chlorine (radical reaction).

Uses and Reactivity of Alkyl Halides

• Reactive compounds useful in various types of chemistry.
• Good electrophiles due to polarizable bond.
• Can break C-X bond to form a halide anion (good leaving group).
• Undergo substitution and elimination reactions.

Reactions with Alkyl Halides

• Nucleophilic Substitution Reactions:
  • Alkyl halide treated with nucleophiles.
  • Substitution involves replacing halide with nucleophile to form a bond.
  • Types: SN2 and SN1 (focus on SN1 in this lecture).
• Elimination Reactions:
  • Involves interaction with a base, losing halogen and hydrogen.
  • Forms an alkene.
  • Focus on E2 reaction in subsequent lecture.

Summary

• Focus on substitution and elimination reactions (not addition).
• Upcoming lectures will explore SN1 substitution and E2 elimination.