Organic Formulae (CIE IGCSE Chemistry)

• Organic Chemistry is the scientific study of the structure, properties, and reactions of organic compounds.
• Organic compounds are those which contain carbon
• For conventional reasons metal carbonates, carbon dioxide and carbon monoxide are not included in organic compounds
• Many of the structures you will be drawing are hydrocarbons
• A hydrocarbon is a compound that contains only hydrogen and carbon atoms
• Organic compounds can be represented in a number of ways:
  • Displayed Formulae
  • General Formulae
  • Structural Formulae

The displayed formula shows the spatial arrangement of all the atoms and bonds in a molecule

• For example:
  
  

• This displayed formula tells us several things about the compound
  • It has 5 carbon atoms
  • It has 12 hydrogen atoms
  • It has only single bonds 

EXTENDED

• In structural formulae, enough information is shown to make the structure clear, but most of the actual covalent bonds are omitted
• Only important bonds are always shown, such as double and triple bonds
• Identical groups can be bracketed together
• Side groups are also shown using brackets
• Straight chain alkanes are shown as follows:
  
  

 

Structural Isomers

• Structural isomers are compounds that have the same molecular formula but different structural formulae
• The molecular formula is the actual number of atoms of each element in a compound
• Compounds with the same molecular formula can have different structural formulae due to the different arrangement of their atoms in space
• Two examples of structural isomers are shown below 

Table showing Structural Isomerism in C₄H₁₀

Table showing Structural Isomerism in C₄H₈