Structural formula
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Many chemical compounds, especially hydrocarbons, can exist in different geometric configurations. A structural formula represents the arrangements of atoms in a way that a chemical formula cannot.
One of the advantages with structural formulae is the ability to tell the structure of the compound (see isomer). A simple example of this may be seen with the hydrocarbon butane, C4H10. The four carbons may be arranged in a linear pattern, or in a branched, "T" pattern. The first arrangement is known as orthobutane or n-butane, while the second is isobutane.
Molecular formula: C4H10.
Structural formulae:
Note that for organic compounds, line drawings of structural formula are assumed to have carbon atoms at the vertices and termini of all line segments not marked with the atomic symbol of an element (other than carbon). Each carbon atom is in turn assumed to bear enough hydrogen atoms to give the carbon atom four bonds. Equivalent full and abbreviated forms are shown in the adjacent figures.
A structural formula can be precisely described using IUPAC nomenclature. In the case of isobutane, the proper IUPAC name is methylpropane.
Multiple planes
When substituents of a molecule exist in different planes, their position can be described using solid and dotted wedges, with the former showing a substituent coming out of the plane, and the latter going into it. This system is useful in describing differences between chiral molecules.
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