Organic Chemistry

• Homologous Series 


  Fossil Fuels and living things are based on carbon.

  Organic chemicals are mostly obtained from crude oil.

  Carbon atoms can form 4 covalent bonds.

  Chain of carbon atoms can form when carbon atoms covalently bond with others.

  This means that there are large numbers of carbon compounds grouped in homologous series
• A homologous series is a family of organic compounds where members

  • Have the same general formula
  • Show similar chemical properties
  • Show a gradation in their physical properties
  • Differ successively by CH2 unit
• General formulae for organic compounds

  This is a formula involves a variable number ,n, which allows the molecular formula of any compound in a homologous series to be determined

  • Alkanes are relatively unreactive. General formula is CnH2n+n
  • Alkenes are more reactive than alkanes. General formula is CnH2n
  • Alcohols and carboxylic acids are reactive organic compounds.
  • Alcohols have general formula CnH2n+1OH
  • Carboxylic acids have the general formula CnH2nO2
• Organic compounds

  • For organic compounds containing one carbon atom, meth- is used
  • For organic compounds containing two carbon atoms, eth- is used
  • For organic compounds containing three carbon atoms, prop- is used
  • For organic compounds containing four carbon atoms, but- is used
• Organic compound names


  • Numbers are required within the name due to the position of a group such as OH and C=C, in the carbon chain
• Alkenes with 4 carbon atoms


  • but-1-ene (C=C starting at carbon 1)
  • but-2-ene (C=C starting at carbon 2)
  • but-3-ene (C=C starting at carbon 3, same as but-1-ene counting from the other end)
• Alcohols with 3 carbon atoms

  • propan-1-ol (OH group at carbon 1)
  • propan-2-ol (OH group at carbon 2)
• The OH bonded to carbon 3 is the same as the OH group bonded in carbon 1
• Drawing structural formulae for organic molecules

  • A structural formula shows the covalent bonds between atoms in a molecule
  • Atoms are presented using the symbol
  • A line (-) is used to represent single covalent bond
  • A = is used to represent double covalent bond
  • Carbon atoms can form 4 covalent bonds. Double bond counts as 2
  • Hydrogen atoms can only form 1 covalent bond
  • Oxygen atoms can form 2 covalent bonds so there should be two lines to an O atom
• Hydrocarbons 


  A hydrocarbon is a compound consisting of hydrogen and carbon only
• Alkanes 


  Have a general formula Cn2n+2. They are saturated hydrocarbons. This means that the molecules do not contain any carbon-carbon double bonds. Unsaturated hydrocarbons contain at least one C=C

  • Methane, ethane, propane and butane
• Methane

  • CH4
  • Gas at room temperature and pressure
  • H
  • H - C - H
  • H
• Ethane

  • C2H6
  • Gas at room temperature and pressure
  • H H
  • H - C - C -H
  • H H
• Propane

  • C3H8
  • Gas at room temperature and pressure
  • H H H
  • H - C - C - C - H
  • H H H
• Butane

  • C4H10
  • Gas at room temperature and pressure
  • H H H H
  • H - C - C - C - C - H
  • H H H H
• Fractional Distillation of Crude Oil

  • This separates crude oil into simpler mixtures of hydrocarbons called fractions. Fractional Distillation is carried out in a fractionating column
  • The crude oil enters at the bottom as a hot, gaseous mixture.
  • The fractionating column has bubble caps which allow gases to move upwards
  • Temperature decreases up the column
  • As the gases move up the column, hydrocarbons condense when the temperature of the column is the same as their boiling point
• Major fractions obtained from crude oil in order of increasing size of molecules and increasing boiling point

  • Refinery gases - used for bottled gases
  • Petrol - used for fuel for cars
  • Naphtha - used for chemicals and plastics
  • Kerosene - used for fuel for aircraft’s
  • Diesel - used for fuel for cars and trains
  • Fuel oil - used for fuel for ships
  • Bitumen - used for surfacing roads as road tar and sealing roofs
• Crude oil is a finite source 


  This means it will run out. Fractions obtained from crude oil contain hydrocarbon, many are used as fuels but also act as feedstock for the petrochemical industry. This means they are used as a starting point for the synthesis of other chemicals such as polymers and pharmaceutical drugs
• Cracking Definition 


  This is the breakdown of larger less useful saturated hydrocarbons into smaller ones that are more useful, some are unsaturated
• Cracking

  • Larger hydrocarbon molecules aren’t as useful as smaller ones. This is because they are not as useful as fuels. They are therefore broken down by cracking
  • Cracking uses heat in the absence of air or a catalyst. If heat is used, it is thermal cracking. If catalyst is used, it is catalytic cracking
  • Equations only involve hydrocarbons but they must have the same number of carbon and hydrogen on left and right
  • Products must include one alkene because there are not enough hydrogen atoms for all products to be alkanes
• Example 1 of cracking

  Octane (C8H18) can be cracked to form butane and ethene (C2H4). Write a balanced symbol equation

  • C8H18 -> C4H10 + 2C2H4
• Example 2 of Cracking 


  Nonane (C9H20) is cracked to form hexane (C6H14) and one other product. Find the other product

  • C9H20 -> C6H14 + CxHy
  • C9H20 -> C6H14 + C3H6
• Alkenes

  • Unsaturated as they contain carbon to carbon double bonds
  • General formula is CnH2n
  • Ethene, propene, but-1-ene and but-2-ene are alkenes
• Ethene

  • C2H4
  • Gas at room temperature and pressure
  • H H
  • C = C
  • H H
• Propene

  • C3H6
  • gas at room temperature and pressure
  • H H
  • C = C - C -H
  • H H H
• But-1-ene

  • C4H8
  • gas at room temperature and pressure
  • H H H
  • C = C - C - C - H
  • H H H H
• But-2-ene

  • C4H8
  • gas at room temperature
  • H H
  • H - C - C = C - C - H
  • H H H H
• Alkenes information

  • But-1-ene and But-2-ene have the same molecular formula but have different structural formula
  • But-1-ene is used because the C=C starts from the first carbon in the chain
  • In But-2-ene, C=C starts the second carbon atom. The lowest number is taken counting from either end
• Example of alkene 


  Compounds with 6 carbon atoms begins with prefix hex-. Suggest a chemical name for this organic molecule

  H. H. H. H.

  H - C - C = C - C - C - C - H

  H. H. H. H. H. H

  This is an alkene because it has C=C, so it is hexene. C=C starts at carbon 2 atom from left and carbon 4 from right. Lowest number is used so it is hex-2-ane
• Alcohols 


  The general formula is CnH2n+1OH

  • methanol
  • ethanol
  • propan-1-ol
  • propan-2-ol
• Methanol

  • CH3OH
  • liquid at room temperature and pressure
  • H
  • H - C - OH
  • H
• Ethanol

  • C2H5OH
  • liquid at room temperature and pressure
  • H H
  • H - C - C - OH
  • H H
• Propan-1-ol

  • C3H7OH
  • liquid at room temperature and pressure
  • H H H
  • H - C - C - C - OH
  • H H H
• Propan-2-ol

  • C3H7OH
  • liquid at room temperature and pressure
  • H H H
  • H - C - C - C - H
  • H OH H
• Alcohol details

  • Presence of bond between O and H atom depends on the question
  • If the question asks all bonds to be shown, there should be a bond between O and H shown as -OH
  • Propan-1-ol and Propan-2-ol have the same molecular formula but different structural formula
  • Propan-1-ol is used because OH is bonded to the first carbon atom
  • Propan-2-ol, the OH is bonded to the second carbon atom
• Alcohol Example 


  Organic compounds with five carbon atoms begin with pent- find the chemical name for this organic molecule

  H. H. H. H. H

  H - C - C - C - C - C - H

  H. H. H. OH. H

  It is pentan-2-ol’ as the OH is bonded to carbon 2
• Carboxylic acids 


  General formula is CnH2nO2

  Often written as COOH, so carboxylic acids with 3 carbon atoms have a molecular formula C3H6O2 but can be written as C2H5COOH

  • Methanoic acid , ethanoic acid , propanoic acid and butanoic acid
• Methanoic acid

  • HCOOH
  • Liquid at room temperature and pressure
  • O (double bond, = , between C and O
  • H - C -
  • OH
• Ethanoic acid

  • CH3COOH
  • liquid at room temperature and pressure
  • H O (= between C and O )
  • H - C - C
  • H OH
• Propanoic Acid

  • C2H5COOH
  • liquid at room temperature and pressure
  • H H O (= between C and O )
  • H - C - C - C
  • H H OH