Which of the following is not one of the first five alkanes?

In the context of hydrocarbons, the first five alkanes are defined by their molecular formulas and consist of the following: methane (one carbon), ethane (two carbons), propane (three carbons), butane (four carbons), and pentane (five carbons). Each of these alkanes follows the general formula of (C_nH_{2n+2}), where (n) is the number of carbon atoms.

Hexane, which has six carbon atoms, is not included in the first five alkanes. It follows butane and pentane in terms of carbon count and is therefore outside the specified range of the first five alkanes. Understanding the sequential nature of alkanes based on the increase in carbon atoms is crucial in distinguishing between them. This highlights the significance of molecular structure when discussing organic compounds.