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:
     $C<em>2H</em>6 <br /> ightarrow C<em>2H</em>4 + H_2$

2. Addition Reactions:

   • Reaction with HBr:
     $C<em>2H</em>4 + HBr <br /> ightarrow C<em>3H</em>7Br$
   • Reaction with Br2:
     $C<em>2H</em>4 + Br<em>2 ightarrow C</em>2Br_2$

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:
  • $C<em>nH</em>{2n-2}$
  • Indicate at least one carbon-carbon triple bond.
  • Examples:
  • 1-butyne
  • 2-butyne

Production of Acetylene

• Reaction:
  $CaC<em>2 + 2 H</em>2O <br /> ightarrow C<em>2H</em>2 + Ca(OH)_2$

Alkyne Reactions

1. Hydrogenation:

   • Reaction:
     $C riple{C} + H_2 <br /> ightarrow C=C$

2. Addition Reactions:

   • Reaction with HBr:
     $C riple{C} + HBr <br /> ightarrow CH_2=CHBr$
   • Reaction with Br2:
     $C riple{C} + Br_2 <br /> ightarrow CHBr=CHBr$
   • Reaction with 2Br2:
     $C riple{C} + 2 Br<em>2 ightarrow CHBr</em>2-CHBr_2$

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:
  • $C<em>nH</em>{2n}$

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.