Structural isomerism in hydrocarbons

It is always difficult to draw on paper a three-dimensional diagram, so generally the zig-zag arrangement of the carbon chain is simplified to a straight line, or what is called a projection formula. 

Both of the butane structures have 4 carbon atoms and 10 hydrogens, but the atoms are arranged in a different sequence, which means that they will be different compounds with somewhat different properties -different boiling and melting points, for example. 

Compounds having the same molecular formula but different sequences of atoms or groups and therefore different structural formulae are called structural isomers. 

As we shall see, there are several different types of structural isomer. Isomers have to be named so that you can tell the difference between them. Consider the first member of the alkane series that shows structural isomerism, butane. 

Obviously the two isomers of C4H10 cannot both be called butane . All of the alkanes larger than propane exhibit isomerism, and there is a system for naming them. The isomer in which the carbon atoms are arranged in a continuous chain is the normal isomer and is just called butane (as shown in the two figures above). 

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