Comparing Alkanes and Alkenes: Reactivity and Why

When it comes to comparing the reactivity of alkanes and alkenes, alkenes are generally more reactive than alkanes. Understanding the structural differences between these two classes of hydrocarbons provides insight into their reactivity and the types of chemical reactions they undergo.

Alkanes

Structure: Alkanes are saturated hydrocarbons, meaning they contain only single bonds between carbon atoms. Their general formula is CnH2n-2. This saturation makes alkanes relatively stable and unreactive.

Reactivity: Alkanes are known for their stability and their ability to undergo only a limited number of reactions such as combustion and free radical halogenation under specific conditions like heat or light. These reactions break the strong covalent bonds within alkanes.

Alkenes

Structure: Alkenes are unsaturated hydrocarbons that contain at least one carbon-carbon double bond (CC). Their general formula is CnH2n. The presence of the double bond significantly affects their reactivity.

Reactivity: The presence of the double bond in alkenes makes them more reactive than alkanes. The double bond is a region of higher electron density, which facilitates the participation of alkenes in various addition reactions such as hydrogenation, halogenation, and oxidation.

Summary

Most Reactive: Alkenes, due to the presence of the double bond and the greater number of potential reaction sites.

Least Reactive: Alkanes, due to their saturated nature and stable single bonds.

In summary, the reactivity of alkenes results from their unsaturation, providing specific sites for chemical reactions that alkanes do not possess. This contrasts the general stability and limited reactivity of alkanes, as further highlighted by the ease with which alkanes can be oxidized to carbon dioxide and water.

To understand this concept better, let's consider the difference between alkanes and alkenes in terms of their chemical reactivity. Alkanes, saturated with respect to their hydrogen content, require breaking a strong C-H bond for any reaction. On the other hand, alkenes, unsaturated and containing a relatively reactive CC double bond, undergo reactions that involve making new bonds.

Alkenes: The unsaturation in alkenes makes them more reactive due to the ability to undergo addition reactions. Any reactivity in alkenes involves not just breaking bonds, but also forming new ones, which is why they are classified as more reactive than alkanes. This is fundamentally due to the nature of the double bond, which is more susceptible to chemical interactions.