Organic chemistry

• Physical properties of compounds depend on

  • Strength of Intermolecular forces
• Stronger intermolecular forces result in

  • Higher boiling points
  • Higher melting points
  • Larger viscosities
  • Lower vapour pressures
• Hydrogen bonds

  • Exist only between molecules of alcohols & molecules of carboxylic acids
• London forces (induced dipole)

  • Exist between all organic molecules
  • Hydrocarbons have London forces ONLY as they are non-polar
  • A temporary dipole is induced due to an uneven distribution of charge when these molecules interact
  • Increases as chain length increases
• Dipole-dipole forces

  • Exist between polar molecules with permanent dipoles
  • Force of attraction between the poles of the molecules
• Hydrogen bonding

  • Strongest IMF
  • Exists between polar molecules like alcohols and carboxylic acids
• Combustion (oxidation)

  1. Organic molecule (coal, oil, gas) is combined (burning in air)

  2. Alkanes are used as fuels with excess oxygen

  3. Produces carbon dioxide, water vapour, and energy

  4. Exothermic
• London forces can increase with greater contact surface and work with greater force of attraction
• Branching decreases IMF
• Increasing chain length increases strength of intermolecular forces, boiling point, melting point, and decreases vapour pressure
• Combustion reactions are highly exothermic and release large amounts of energy
• Combustion

  1. Organic molecule (coal, oil, gas) is combined and burned in air

  2. Alkanes are used as fuels with excess oxygen to produce carbon dioxide, water vapour, and energy

  3. Combustion reactions are highly exothermic, producing large amounts of heat or energy

  4. Common combustion reaction is the process of cellular respiration: Alkane + O₂ → CO₂ + H₂O + energy
• Types of Reactions

  • Addition reaction: double bond/triple bond in the starting material is broken and elements are added
  • Substitution reaction: group of atoms in a molecule is replaced by another group
  • Elimination reaction: elements of the starting material break up to give two products
• Addition reactions

  • Take place in unsaturated compounds like Alkenes, Alkynes
  • Involve breaking of double or triple bonds to produce saturated compounds
  • Take place faster than substitution reactions
  • Follow Markovnikov's rule
• Hydrogenation

  1. Adding H₂ across a carbon-carbon double or triple bond to form an alkane

  2. Occurs with alkene dissolved in a non-polar solvent with Pt, Pd, or Ni used as catalyst
• Halogenation

  1. Adding halogen (Br₂, Cl₂, I₂) across an alkene to form a haloalkane

  2. Occurs in an unreactive solvent with halogen dissolved in CCl₂
• Hydrohalogenation

  1. Adding a hydrogen halide (HX) to a molecule

  2. Forms the main product and by-product depending on if the alkene is symmetrical
• Hydration

  1. Adding water to an alkene to form an alcohol

  2. Major product determined by Markovnikov's rule

  3. Reaction conditions: excess H₂O, small amount of acid as catalyst
• Hydration

  Adding water to an alkene forms an alcohol
• Elimination Reactions

  • The number of double/triple bonds increase
  • Increase the total number of molecules
• Dehydration

  • Removal of water from an alcohol to form an alkene
  • Main product: alkene
  • By-product: water
• Cracking

  • Breaking up large molecules into smaller ones
  • Short chain alkanes and alkenes are more useful
• Thermal cracking

  High pressure and temperature
• Catalytic cracking

  Low pressure and temperature
• Halogenation

  OH in alcohol replaced by halogen to form a haloalkane
• Halogenation

  • OH in alcohol replaced by halogen to form a haloalkane
  • Solid NaBr and H₂SO₄ used as catalyst
• Hydrolysis

  HBr reacts with alcohol to form haloalkanes and water
• Classification of hydrocarbons

  • Hydrocarbons
  • Alkanes
  • Alkenes
  • Alkynes
• Saturated hydrocarbons

  Have single carbon-carbon (-C-C-) bonds only
• Unsaturated hydrocarbons

  Have one or more multiple carbon-carbon bonds (double or triple bonds)
• Homologous series

  • Alkanes CH2n+2
  • Alkenes CH2n
  • Alkynes CH2n-2
  • Alcohols CnH2n+1
  • Haloalkanes CHnX 2n+1
  • Aldehydes CHO
  • Ketones CnH2n
  • Carboxylic acids CnH2nO2
  • Esters
• Physical properties of Alkanes

  • Essentially non-polar
  • Boiling point increases as the number of carbon chains increase
  • Have low density; most are less dense than water
  • Immiscible (not soluble) with water
• Chemical properties of Alkanes

  • Low chemical reactivity
  • Combustion reaction is the most important chemical reaction of alkanes
  • Highly exothermic
  • Most important fuel chemicals
• Chemical properties of Alkenes and Alkynes

  • 'ene' indicates a double bond
  • 'yne' indicates a triple bond
• Most important Fuel chemicals

  • Alkenes
  • Alkynes
• 'ene


  Indicates a double bond
• 'yne


  Indicates a triple bond
• Haloalkane names

  • Fluoro
  • Chloro
  • Bromo
  • Iodo
• 1. bromopropane structure

  • CH3-CH2-CH2-Br
• Alcohols

  • Functional group is called hydroxyl
  • Properties: Flammable, poisonous, polar, soluble in water, high melting/boiling points, hydrogen bonding sites, solubility decreases with chain length