7.2._Reactions_of_alkenes_and_alcohols

Topic 7: Organic Chemistry

Reactions of Alkenes and Alcohols (Higher Tier Content Only)

Page 1

• Overview of organic chemistry, focusing on reactions of alkenes and alcohols.

Page 2: Structure and Formulae of Alkenes

• General Formula: ( C_nH_{2n} )

• Characteristics:

  • At least one carbon-carbon double bond (C=C) making them unsaturated.

  • Contains two fewer hydrogen atoms than the corresponding alkane.

• Examples of Alkenes:

  • Ethene (C2H4)

  • Propene (C3H6)

  • Butene (C4H8)

  • Pentene (C5H10)

• Reactions of Alkenes:

  • Alkenes react with oxygen in combustion, producing smoky flames due to incomplete combustion.

  • React with hydrogen, water, and halogens (Br2, Cl2, I2) via addition reactions:

    • Ethene + Bromine: ( C_2H_4 + Br_2 )

    • Propene + Water: ( C_3H_6 + H_2O ) → Propanol

    • Butene + Hydrogen: ( C_4H_8 + H_2 ) → Butane

Page 3: Reactions Continued

• Mechanism of Reactions:

  • C=C bond is broken to form a C-C bond.

  • The added compound splits into two groups that are bonded to different carbons in the original double bond.

• Alcohols Overview:

• Alcohols contain the functional group -OH.

• Examples of Alcohols:

  • Methanol (CH3OH)

  • Ethanol (C2H5OH)

  • Propanol (C3H7OH)

  • Butanol (C4H9OH)

• Representation of Alcohols:

  • Structural formulae highlighting the -OH group.

Page 4: Reactions of Alcohols

• Combustion:

  • Alcohols burn in air, producing carbon dioxide and water.

• Solubility:

  • Dissolve in water to form a neutral solution with pH 7.

• Reactions with Sodium:

  • React to produce hydrogen and a salt (e.g., C2H5ONa).

• Oxidation:

  • React with oxidizing agents to form carboxylic acids.

• Uses of Alcohols:

  • Methanol: chemical feedstock, anti-freeze, biodiesel production.

  • Ethanol: main alcohol in beverages, solvents, and fuels.

  • All four alcohols can be utilized as fuels.

• Production of Ethanol:

  • Produced by fermentation of sugar with yeast.

  • Conditions: ~35°C, anaerobic, with yeast as a catalyst.

  • Reaction: Sugar → Ethanol + Carbon Dioxide

Page 5: Carboxylic Acids

• Functional Group: Carboxyl group -COOH.

• Examples of Carboxylic Acids:

  • Methanoic acid (HCOOH)

  • Ethanoic acid (CH3COOH)

  • Propanoic acid (C2H5COOH)

  • Butanoic acid (C3H7COOH)

• Reactions of Carboxylic Acids:

  • Dissolve in water producing acidic solutions (pH < 7).

  • React with metal carbonates to produce carbon dioxide (turns limewater cloudy), a salt, and water.

  • React with alcohols in the presence of an acid catalyst to produce esters.

  • Weak Acids:

    • Do not ionize completely in solutions, resulting in fewer H+ ions, making them weaker acids than strong acids of the same concentration.