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13B Representing organic molecules

What you should be able to do:
  • interpret and use the general, structural, displayed and skeletal formulae of organic molecules

Different ways to represent an organic molecule

types of organic formula: molecular formula, empirical formula, structural formula, displayed formula, skeletal formula

Molecular and empirical formulae

A molecular formula shows the number of each atom in a compound, while an empirical formula shows the simplest whole number ratio of the the combining atoms.

CompoundMolecular formulaEmpirical formula
propaneC3H8C3H8
etheneC2H4CH2
propeneC3H6CH2
ethanoic acidC2H4O2CH2O

Structural, displayed and skeletal formulae

While molecular formula only shows the number of each atom in a molecule, structural, displayed and skeletal formulae shows the arrangement of the atoms. A displayed formula shows both the relative position of atoms and the bonds between them. A structural formula shows the relative position of the atoms without showing the bonds. A skeletal formula, the simplest way of representing an organic compound, is similar to

Example 1: butane (C4H10)

displayed, structural and skeletal formulae of propane
displayed, structural and skeletal formulae of butane

Note that the displayed formula does not indicate the bond angles.

Example 2: 4-chloro-3-methylpentan-1-ol (C6H13ClO)

structural, displayed and skeletal formulae of 4-chloro-3-methylpentan-1-ol
displayed, structural and skeletal formulae of 4-chloro-2-methylpentan-1-ol

Example 3: ethyl propanoate (C5H10O2)

structural, displayed and skeletal formulae of ethyl propanoate

Test yourself

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