An infinite variety of compounds can be assembled from only carbon and hydrogen atoms. Such hydrocarbons are the simplest organic compounds, but they are also of prime economic importance because they include the constituents of petroleum and natural gas.
Propane, butane, and isobutane are all hydrocarbons with only single covalent bonds between carbon atoms. These hydrocarbons that lack double bonds, triple bonds, or ring structures make up the class called alkanes. See Table 1.
As the number of carbon atoms increases, so does the number of ways that they can be connected to form different isomers. You should realize that isomers are defined by the pattern of bonding between the carbons.
The two molecules in Figure 1 are not different isomers; they are both butane. Despite the crooked carbon chain of the molecule on the right, it still has the same condensed structural formula, as shown in Figure 2.
Figure 1. Both molecules are the same isomer of butane.