organic chem

• Types of Reaction


  • Addition
  • Elimination
  • Substitution
  • Oxidation
  • Reduction
  • Hydrolysis
  • Polymerisation
• Addition reactions


  • Two reactants combining to form one product
• Elimination reactions


  • One or two reactants forming more products, often including an alkene and a smaller molecule that has been eliminated from the reactant
• Substitution reactions


  • An atom or group of atoms in a compound is replaced by another atom or group of atoms
• Oxidation reactions


  • Involve the loss of hydrogen or the gain of oxygen, where a reactant is oxidised by another chemical species
• Reduction reactions


  • Involve the gain of hydrogen or the loss of oxygen, where a reactant is reduced by another chemical species
• Hydrolysis reactions


  • Specific reactions with water, where a compound is split by water
• Polymerisation reactions


  • At AS level, addition polymerisation where the carbon-carbon double bond of an alkene monomer breaks open and forms a polymer chain
• Bond polarity can be used to suggest reaction mechanisms

  • Non-polar or slightly polar bonds suggest homolytic fission and free radical mechanisms
  • Polar bonds suggest heterolytic fission and mechanisms involving electrophiles or nucleophiles
• Classifying halogenoalkanes


  Primary: halogen attached to carbon with 1 other alkyl group. Secondary: halogen attached to carbon with 2 other alkyl groups. Tertiary: halogen attached to carbon with 3 other alkyl groups.
• Nucleophile


  An electron-rich species that can donate a pair of electrons
• Nucleophilic


  Referring to reactions that involve a nucleophile
• Formation of alcohols


  1. Nucleophile is hydroxide ion (OH-)

  2. Reaction with aqueous sodium/potassium hydroxide

  3. Produces an alcohol

  4. Rate depends on type of halogen (C-F > C-Cl > C-Br > C-I)
• Reaction with water


  1. Water is a weak nucleophile

  2. Slowly substitutes halogen to produce an alcohol

  3. Silver nitrate solution can be used to precipitate halide ions
• Formation of nitriles


  1. Nucleophile is cyanide ion (CN-)

  2. Reaction with ethanolic potassium cyanide

  3. Produces a nitrile
• Formation of primary amines by reaction with ammonia

  1. Nucleophile is ammonia (NH3)

  2. Reaction with ethanolic ammonia under pressure

  3. Produces a primary amine
• Formation of alkenes


  1. Reaction with ethanolic sodium hydroxide and heat

  2. Produces an alkene by eliminating hydrogen halide
• Nucleophilic substitution reaction


  A nucleophile attacks a carbon atom with a partial positive charge, replacing an atom with a partial negative charge
• Measuring the rate of hydrolysis

  • Using acidified aqueous silver nitrate to form precipitates
  • Faster rate for iodoalkanes, slower for chloroalkanes
• Carbon-halogen bond polarity


  • Carbon has δ+ charge, halogen has δ- charge
  • Polarity decreases down the group
• Bond enthalpy


  • C-I bond weakest, C-F bond strongest
  • Determines reactivity in substitution reactions
• Alcohols


  Molecules that contain the hydroxyl functional group, -OH
• Nomenclature of alcohols


  Alkan + ol
• Diol


  Molecule with two -OH groups
• First four alcohols and their structures

  • Methanol
  • Ethanol
  • Propanol
  • Butanol
• Classification of alcohols


  • Primary (carbon atom bonded to -OH is attached to one other carbon)
  • Secondary (carbon atom bonded to -OH is attached to two other carbons)
  • Tertiary (carbon atom bonded to -OH is attached to three other carbons)
• Combustion of alcohols


  Alcohol + oxygen → carbon dioxide + water
• Conversion to halogenoalkanes


  1. Chlorination (using PCl5 or HCl)

  2. Bromination (using KBr and H2SO4)

  3. Iodination (using red phosphorus and iodine)
• Dehydration to alkenes


  Heating alcohol with concentrated phosphoric acid
• Oxidation of alcohols


  • Primary alcohols can be oxidised to aldehydes and then carboxylic acids
  • Secondary alcohols can be oxidised to ketones
  • Tertiary alcohols do not undergo oxidation
• Oxidising agents for alcohols

  • Acidified K2Cr2O7 (orange solution reduced to green Cr3+ ions)
  • Fehling's solution (alkaline solution containing Cu2+ ions)
  • Tollens' reagent (ammoniacal silver nitrate solution)
• Aldehydes can be detected by Fehling's and Tollens' reagents, which give positive tests, while ketones give negative tests
• Reflux


  Heating organic reactions to complete them without loss of reactants, products or solvent
• Heating under reflux


  1. Place reaction mixture in flask

  2. Add anti-bumping granules

  3. Heat using mantle or water bath

  4. Set up quick-fit apparatus with condenser

  5. Maintain steady stream of cooling water through condenser

  6. Heat until reaction complete

  7. Allow to cool
• Reactions using heating under reflux

  • Production of carboxylic acid from primary alcohol
  • Production of ester from alcohol and acid
• Distillation


  Separating compounds by boiling point
• Distillation process


  1. Place reaction mixture in flask

  2. Add anti-bumping granules

  3. Set up quick-fit apparatus with still head and condenser

  4. Grease joints

  5. Use thermometer to monitor temperature

  6. Maintain steady stream of cooling water through condenser

  7. Heat until desired product distils over

  8. Collect distillate at correct temperature range
• Solvent extraction


  Purifying organic compounds by separating layers in a separating funnel
• Solvent extraction using separating funnel

  1. Transfer reaction mixture to separating funnel

  2. Invert and open stopcock to release pressure

  3. Allow layers to separate

  4. Drain off aqueous layer

  5. Collect organic layer
• Drying agents


  Anhydrous inorganic salts that absorb water from organic products