Aldehydes and ketones

• Acidified potassium dichromate is the oxidising agent for alcohols
• primary alcohols oxidises into aldehydes and then into carboxylic acids
• secondary alcohols oxidises into ketones
• Why doesn't tertiary alcohols oxidise?

  because they don't have a oxygen attached to their carbonyl
• Test for alcohols

  Potassium dichromate

  • orange to green
  • stays orange if it is a tertiary alcohol
• test for Aldehyde

  Fehling's solution

  • red precipitate

  Tollen's solution

  • silver mirror
• How to make the Tollen's reagent?

  aqueous ammonia and silver nitrate
• NaBH4 is the reagent for reduction of alcohols
• aldehydes reduce to primary alcohol
• Ketones reduce to secondary alcohol
• reagent and condition for reduction of alcohols

  NaBH4 in aqueous ethanol at room temp and pressure
• What does carboxylic acids get reduced to?


  aldehyde and then primary alcohol
• intermolecular force in carbonyls and why


  permanent dipole, because the cannot hydrogen bond to themselves
• Smaller carbonyls are soluble in water because they can form hydrogen bonds
• Why is C=O bond polarised?


  because O2 is more electronegative than carbon, positive carbon attract nucleophiles
• Why doesn't carbonyls undergo addition reaction as easily as alkenes?


  C=O bonds are stronger than C=C bonds
• Why are C=C bonds more attracted by electrophiles than C=O bonds?


  less strong
• NaBH4 contains source of nucleophilic hydride ions, attracted to positive carbon in C=O bonds
• Mechanism that reduce carbonyls 


  nucleophilic addition
• Other way to reduce carbonyls


  Catalytic hydrogention
• reagent and condition for catalytic hydrogenation


  Hydrogen and nickel catalyst at high pressure
• What does addition of cyanide produce?


  hydroxynitriles
• Reagent and condition for addition of cyanide

  Sodium cyanide and dilute H2SO4 at room temp and pressure
• HCN gas is toxic, hard to contain
• KCN and NaCN has higher concentration of CN- ions, completely ionise. HCN is a weak acid only partially dissociates
• Why does nucleophilic addition of CN to carbonyls produce racemate?


  unsymmetrical, when trigonal planar carbonyl approached from both sides by HCN attacking species
• Why are there no optical isomer activity in addition of CN?

  equal chances of either enantiomers forming so racemate forms
• Distillation separate organic product from reacting mixture
• To maximise yield of distillation, only collect distillate at approximate boiling point (equal or lesser than)
• Why does water go in from the lowest point of the apparatus?


  Go against gravity, prevent back flow and more effective cooling
• Why are electric heaters/ water baths used in distillation?


  Ethanol is highly flammable, will set on fire if close to naked flame
• How to increase yield of distillation?


  Cooled in ice
• Full oxidation oxidises primary alcohols into carboxylic acids
• Conditions and reagent of full oxidation

  potassium dichromate and H2SO4, in excess potassium dichromate and under reflux
• Reflux is used when heating organic reaction for long period. Condenser prevents organic vapour from escaping and condense back into liquid
• Why shouldn't you seal in reflux?


  Built up gas can cause apparatus to explode
• Anti-bumping granules prevent vigorous and uneven boiling, makes small bubbles
• Why is HCN slower rather than KCN or NaCN

  weak acid, partially dissociate, very few CN- ions
• Why is tollen's reagent used over the cheaper potassium dichromate?


  Dichromate will also oxidise, give false positive
• What happens when a reaction mixture is under reflux and why is it necessary, to complete full oxidation?


  A mixture of liquids is heated to boiling over a prolonged time, vapours form which escapes from the liquid mixture is condensed back into liquid and returned into liquid mixture.

  Any ethanol and ethanal that initially evaporates is oxidised