organic qa

• Br2 (aq) can react with alkenes, orange Br2(aq) decolourises (electrophilic addition)
• Br2 (aq) can react with phenol and phenylamine, orange Br2 (aq) decolourises, white ppt formed (electrophilic substitution)
• Neutral FeCl3 can react with phenols to give purple colouration (complex formation)
• aliphatic aldehydes can react with Fehling's solution with heating to give brick-red ppt of Cu2O (oxidation)
• iodoform test:

  • add 1cm3 of iodine (aq) to sample solution, then add NaOH dropwise until brown colour just disappears, warm the mixture with hot water bath
  • yellow ppt formed for positive test
  • oxidation reaction
• KMnO4 (aq), H2SO4 (aq), with warming, purple solution decolourises for:

  • alkene
  • primary and secondary alcohol
  • aldehyde
  • methylbenzene
• K2Cr2O7 (aq), H2SO4 (aq), orange solution turns green for:

  • primary and secondary alcohol
  • aldehyde
• 2,4-dinitrophenylhydrazine (DNPH) can give orange ppt (positive test) with aldehydes and ketones
• Na metal can react with carboxylic acids, alcohols and phenols to give effervescence, H2 gas
• NaCO3 can react with carboxylic acids, effervescence of CO2 gas that will give white ppt with calcium hydroxide
• Na2CO3 can react with phenols, dissolves but no other observable change
• NaOH can react with carboxylic acids and phenols, no observable change
• alcohols and carboxylic acids can react with PCl5 at rtp to give white fumes of HCl (Nucleophilic substitution reaction)
• preparation of Tollens' reagent:

  • add 30 drops of AgNO3, then 5 drops of NaOH, then add NH3 (aq) drop by drop until brown Ag2O just dissolves
• aliphatic and aromatic aldehydes can react with Tollens' reagent upon heating to give silver mirror