As we will soon see in Section 4.5, gasoline is a complex mixture of alkanes and other hydrocarbons, and the term "octane rating" is used as a standard measure of the performance of engine fuel. In the petroleum industry, one area of interest is the use of catalysts to convert unbranched alkanes and branched alkanes with higher octane ratings (Journal of the Japan Petroleum Institute 2004, 47, 1–10). For example, heptane can undergo isomerization in the presence of suitable catalysts to give eight different constitutional isomers, all of which are branched alkanes with the molecular formula C7H16. Draw all eight constitutional isomers, making sure not to draw the same compound twice.