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).