The structure of organic compounds can be represented in various ways. Some examples of different representations of the same alkane are shown below.
The expanded form shows all atoms and bonds, both to carbon and hydrogen.
The condensed form shows all atoms but only shows bonds to atoms or groups of atoms in branches.
The line form shows bonds between carbons with no atom labels.
In the line form of a saturated alkane:
There is a CH3 at the ends of the chain and the ends of lines coming off the chain.
Each peak or trough in the chain is a carbon.
A peak or a trough is a
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| expanded structure (formula) | condensed structure (formula) |
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| line (skeletal) structure (formula) |
The expanded form shows all atoms and bonds, both to carbon and hydrogen.
The cumbersome nature of these is obvious!
The condensed form shows all atoms but only shows bonds to atoms or groups of atoms in branches.
These are more compact to write and still show all of the atoms.
The line form shows bonds between carbons with no atom labels.
These are the quickest to draw but it is important to have an understanding of what the lines represent as described below.
In the line form of a saturated alkane:
There is a CH3 at the ends of the chain and the ends of lines coming off the chain.
Each peak or trough in the chain is a carbon.
A peak or a trough is a
CH2 if two lines (bonds to carbon) extend from it.
CH if three lines (bonds to carbon) extend from it.
There are no examples of that in the structure above.
C (with no H) if four lines (bonds to carbon) extend from it
CH if three lines (bonds to carbon) extend from it.
There are no examples of that in the structure above.
C (with no H) if four lines (bonds to carbon) extend from it