Classification of alcohols

Classification of Alcohols

  • Alcohols are classified based on the number of alkyl groups attached to the carbon bonded to the hydroxyl group.

    • Types of classification:

      • Primary: Alcohols with one alkyl group attached.

      • Secondary: Alcohols with two alkyl groups attached.

      • Tertiary: Alcohols with three alkyl groups attached.

Learning Check 1

  • Task: Classify each alcohol as primary, secondary, or tertiary.

    • Examples provided: A, B, C.

Solution 1

  • Classifications:

    • A: Secondary

    • B: Primary

    • C: Tertiary

Boiling Points of Alcohols

  • Alcohols have distinct properties due to the electronegativity of oxygen:

    • Oxygen Charge: Partial negative charge.

    • Hydrogen Charge: Partial positive charge.

    • Resulting in hydrogen bonds between alcohol molecules, significantly impacting boiling points.

  • Small alcohol and ether molecules are soluble in water due to hydrogen bond formation.

  • Hydrogen bonds are present in alcohol molecules but absent in ether molecules.

Comparing Alcohols and Alkanes

  • Alcohols generally have higher boiling points than alkanes due to their ability to form hydrogen bonds among themselves.

Boiling Points and Solubility of Alcohols and Ethers

  • Key Information Table:

    • Methanol: C₁H₃OH, Boiling Point: 65°C, Water Solubility: Soluble.

    • Ethanol: C₂H₅OH, Boiling Point: 78°C, Water Solubility: Soluble.

    • 1-Propanol: C₃H₇OH, Boiling Point: 97°C, Water Solubility: Soluble.

    • 1-Butanol: C₄H₉OH, Boiling Point: 118°C, Water Solubility: Slightly soluble.

    • 1-Pentanol: C₅H₁₁OH, Boiling Point: 138°C, Water Solubility: Insoluble.

    • Dimethyl ether: C₂H₆O, Boiling Point: -23°C, Water Solubility: Slightly soluble.

    • Ethyl methyl ether: C₄H₁₀O, Boiling Point: 8°C, Water Solubility: Slightly soluble.

    • Diethyl ether: C₄H₁₀O₂, Boiling Point: 35°C, Water Solubility: Slightly soluble.

    • Ethyl propyl ether: C₅H₁₂O, Boiling Point: 64°C, Water Solubility: Insoluble.

Solubility of Alcohols

  • Alcohols contain polar hydroxyl (–OH) groups that facilitate hydrogen bonding with water.

    • Solubility Rule: Alcohols with one to three carbons are soluble in water.

    • As the carbon chain length increases, solubility in water decreases significantly.

Solubility of Ethers Compared to Alcohols

  • Ethers can form hydrogen bonds with water but to a lesser extent:

    • Slightly soluble in water for ethers with fewer than four carbon atoms.

    • Not soluble in water if containing five or more carbon atoms.

Solubility of Phenols in Water

  • Phenols Overview:

    • Slightly soluble in water; possess an –OH group capable of hydrogen bonding.

    • Can react with water to yield phenoxide ions, leading to a slight ionization and weak acidity.

Phenol and Antiseptics

  • Historically used as antiseptics for skin application to eliminate infection-causing microorganisms:

    • Originally dilute solutions of phenol for disinfecting wounds.

    • Modern antiseptics, such as those in Lysol, include compounds like 2-phenylphenol and 2-benzyl-4-chlorophenol.

Chemistry Link to Health: Hand Sanitizers

  • Hand sanitizers often utilize ethanol:

    • Effective against most bacteria and viruses responsible for colds and flu.

    • Typically contain 60% (v/v) to 85% (v/v) ethanol, highly flammable with characteristic blue flames.

    • Triclosan, an antibiotic ingredient, is banned in personal care products.

Learning Check 2

  • Task: Determine solubility in water for specific examples A and B, providing explanations.

    • A: Not soluble (long carbon chain alcohols are nonpolar).

    • B: Soluble (short-chain alcohols can form hydrogen bonds with water).