Chem 2 s2

• Compounds with other principle functional groups - hydroxyl group as substituent
• Example hydroxyl group as substituents

  • C6H4(OH)(OOH)

  2-hydroxybenzoic acid

  • C6H4(OH)(OCH3) 2-hydroxyacetophenone
• Physical properties 1. Colourless, crystalline, poisonous solid with phenolic odor
• Physical properties 2. M.pt: 41°C and B.pt: 182°C
• Physical properties • Completely soluble in water above 68.5°C
• Boiling point • presence of -OH group

  • Form hydrogen bond between hydroxyl group of phenol molecules
• Much higher boiling point than hydrocarbon with similar Mr
• • Acidity phenol > water > alcohol • stability of acid anion increase, acidity increase.
• • The negative charge in alkoxide ion (RO) is confined to oxygen and cannot delocalised. • Then, alkoxide ion (RO) less stable and weaker acid than hydroxide ion (OH ).
• Acidity

  • ROH + H2O <-> RO- + H3O+

  • Benzene-OH + H2O <-> Benzene-O- + H3O+

  • H2O + H2O <-> HO- + H3O+
• Resonance effect:

  • 1 lone pair of e on the oxygen atom is delocalized into benzene ring. • Causes phenoxide ion more stable than alkoxide ion.
• Important

  Benzene-O- (have 3 lone pair) -> Benzene-O- (have 2 lone pair), (one lone pair at benzene ring), (structure benzene that have 2 line just have 2 rather than normal, 3 )
• Acidity

  Phenol > benzene methanol > benzene ethanol > cyclohexanol
• Acidity

  Methanol > ethanol > propanol