Advanced Placement (AP) Biology Practice Exam

How do functional groups affect hydrocarbons?

1. They make them more stable.

2. They increase their reactivity.

3. They decrease their solubility.

4. They have no effect on them.

The correct answer is: They increase their reactivity.

Functional groups play a significant role in defining the chemical properties and reactivity of hydrocarbons. When a functional group is added to a hydrocarbon, it transforms the molecule into a more reactive species due to the electronegative elements or specific arrangements of atoms present in the functional group. These groups often introduce polar characteristics to the molecule, enabling them to participate in chemical reactions that hydrocarbons alone would not undergo. For instance, adding a hydroxyl (-OH) group turns a hydrocarbon into an alcohol, increasing its reactivity by allowing it to engage in hydrogen bonding, which subsequently affects its physical properties like boiling point and solubility in water. Similarly, carboxylic acids, amino groups, and others modify the molecule's reactivity, making them crucial in organic reactions and metabolic processes. Thus, the presence of functional groups enhances the chemical activity of hydrocarbons, leading to their involvement in a broader range of biological and synthetic reactions.