Organic Chemistry: Alkenes, Alkynes, and Aromatic Compounds

Alkenes and Alkynes Reactions

• Objectives:
  • Analyze geometric isomers
  • Apply reactions of alkenes
  • Apply reactions of alkynes

Common Elements in Organic Compounds

• Organic compounds primarily contain the following elements:
  • Carbon (C)
  • Hydrogen (H)
  • Other common elements include:
  • Oxygen (O)
  • Nitrogen (N)
  • Sulfur (S)
  • Phosphorus (P)
  • Halogens (F, Cl, Br, I)

Geometric Isomers

• Definition:

  • Isomers that have the same molecular formula but differ in the spatial arrangement of atoms.

• Examples of Geometric Isomers:

  • cis-Dichloroethylene:

  • Structure:

    CI H
    \ |
    C=C
    / |
    H CI

  • trans-Dichloroethylene:

  • Structure:

    CI H
    \ /
    C=C
    / \
    H CI

Alkene Reactions

General Reactions

1. Cracking Reaction:

   • Catalyst: Pt
   • Reaction:
     C2H6
     ightarrow C2H4 + H_2

2. Addition Reactions:

   • Reaction with HBr:
     C2H4 + HBr
     ightarrow C3H7Br
   • Reaction with Br2:
     C2H4 + Br2 ightarrow C2Br_2

Markovnikov’s Rule

• Definition:
  • In the addition of unsymmetrical reagents to alkenes, the positively charged portion of the reagent adds to the carbon atom that already has the most hydrogen atoms.

Alkynes

• General Formula:
  • CnH{2n-2}
  • Indicate at least one carbon-carbon triple bond.
  • Examples:
  • 1-butyne
  • 2-butyne

Production of Acetylene

• Reaction:
  CaC2 + 2 H2O
  ightarrow C2H2 + Ca(OH)_2

Alkyne Reactions

1. Hydrogenation:

   • Reaction:
     C riple{C} + H_2
     ightarrow C=C

2. Addition Reactions:

   • Reaction with HBr:
     C riple{C} + HBr
     ightarrow CH_2=CHBr
   • Reaction with Br2:
     C riple{C} + Br_2
     ightarrow CHBr=CHBr
   • Reaction with 2Br2:
     C riple{C} + 2 Br2 ightarrow CHBr2-CHBr_2

Hydrocarbons Classification

• Types of Hydrocarbons:
  • Aliphatic: Includes alkanes, cycloalkanes, alkenes, and alkynes.
  • Aromatic: Contains benzene rings.

Cycloalkanes

• Definition:
  • Alkanes in which carbon atoms are bonded in a ring structure.
  • General Formula:
  • CnH{2n}

Aromatic Hydrocarbons

• Characteristics:
  • Contain a benzene ring
  • Exhibit resonance; more stable than non-resonant structures.

Nomenclature of Aromatic Compounds

• Basic Naming of Monosubstituted Benzenes:

  • Easy to replace one hydrogen atom with a functional group.

• Locating Substituents:

  • Number the carbon atoms in the benzene ring to indicate substituent positions.
  • Use prefixes:
  • o- (ortho) for adjacent groups
  • m- (meta) for one carbon apart
  • p- (para) for opposite ends

Functional Groups in Organic Chemistry

• Key Functional Groups:
  • Alcohol - R−OH
  • Ether - R−O−R'
  • Aldehyde - RCHO
  • Ketone - RCOR
  • Carboxylic Acid - RCOOH
  • Ester - R'COOR
  • Amine - RNH_2

Important Summary Points

• Understanding geometric isomers allows for better comprehension of molecular behavior.
• Alkenes follow addition reactions based on unsymmetrical reagents and their substitution rules (Markovnikov's).
• Alkynes are characterized by triple bonds and follow similar reaction patterns as alkenes.
• Knowledge of functional groups is critical for classifying and understanding organic compounds in biochemistry and industry.