Class 12 Chemistry Alcohols, Phenols and Ethers Notes

Class 12 Chemistry Alcohols, Phenols and Ethers Notes

7.1 Classification

  • Alcohols (R–OH): Organic compounds containing –OH group attached to saturated carbon
    • Primary (1°): –OH on primary carbon
    • Secondary (2°): –OH on secondary carbon
    • Tertiary (3°): –OH on tertiary carbon
  • Phenols (Ar–OH): Hydroxyl group directly attached to an aromatic ring
  • Ethers (R–O–R’): Oxygen atom connected to two alkyl or aryl groups

7.2 Nomenclature

Alcohols

  1. IUPAC: Replace –e in alkane with –ol
  2. Number chain so –OH has lowest possible number
  3. Example: CH₃CH₂OH → Ethanol

Phenols

  • Parent benzene ring + –OH → phenol
  • Substituted phenols: Number ring for substituents

Ethers

  1. Name smaller group first as alkoxy
  2. Larger group as parent alkane
  3. Example: CH₃–O–CH₂CH₃ → Methoxyethane

7.3 Structures of Functional Groups

  • Alcohols: –OH attached to sp³ carbon
  • Phenols: –OH attached to sp² carbon of aromatic ring
  • Ethers: Oxygen with two single covalent bonds to carbon

7.4 Alcohols and Phenols

Physical Properties

  • Hydrogen bonding → higher boiling points
  • Soluble in water (short chain alcohols and phenols)

Chemical Properties

Alcohols

  1. Acidic nature: React with metals → form alkoxides
  2. Oxidation:
    • Primary → Aldehydes → Carboxylic acids
    • Secondary → Ketones
    • Tertiary → Resistant
  3. Substitution: RX formation using HX
  4. Esterification: Reaction with carboxylic acids → esters

Phenols

  1. Weakly acidic → form phenoxide ion with bases
  2. Electrophilic substitution reactions at ortho/para positions

7.5 Some Commercially Important Alcohols

  1. Methanol (CH₃OH): Solvent, fuel
  2. Ethanol (C₂H₅OH): Alcoholic beverages, antiseptic, fuel
  3. Glycerol (C₃H₅(OH)₃): Soaps, cosmetics
  4. Ethylene glycol (HO–CH₂–CH₂–OH): Antifreeze

7.6 Ethers

Physical Properties

  • Relatively low boiling points compared to alcohols
  • Poor hydrogen bonding

Chemical Properties

  • Generally less reactive
  • Cleavage by HX: R–O–R + HX → RX + ROH

📌 Important Exam Points

  • Alcohols and phenols show hydrogen bonding
  • Phenols are more acidic than alcohols
  • Oxidation reactions differ for 1°, 2°, and 3° alcohols
  • Ethers are relatively inert but react with strong acids