Representing the formulae of organic compounds

• The molecular formula shows the number and typeof atoms of each element in a molecule. It does not show how the atoms are joined together and different molecules can have the same molecular formula
• The empirical formula is the simplest whole-number ratio of the atoms of each element present in a compound.
• The general formula is the simplest algebraic formula for any member of a homologous series. It can be used to generate the molecular formula of any member of that homologous series.
• General formula of alkanes = $C_nH_2n+$$2$
• General formula of alkenes = $C_nH_2n$
• General formula of alcohols = $C_nH_2n+$$1OH$
• General formula of carboxylic acids = $C_nH_2nO_2$
• General formula of ketones = $C_nH_2nO$
• A displayed formula shows the relative positioning of all the atoms in a molecule and the bonds between them
• The structural formula uses the smallest amount of detail necessary to show the arrangement of the atoms in a molecule. It shows clearly which groups are bonded together. E.g. structural formula of butane: $CH_3CH_2CH_2CH_3$ or $CH_3(CH_2)_2CH_3$
• A skeletal formula is a simplified organic formula. You remove:

  All carbon and hydrogen labels from carbon chains

  Any bonds to hydrogen atoms

  This leaves just a carbon skeleton and any functional groups. In skeletle formulae:

  A line represents a single bond

  An intersection of two lines represents a carbon atom

  The end of a line represents a (-CH_3) group.
• When functional groups are present in a molecule, they must be included in the skeletal formula