AICE Chemistry Practice Exam

Unsaturated hydrocarbons are characterized by the presence of pi bonds, which indicate that the molecule contains one or more double or triple bonds. These pi bonds are formed by the overlap of p orbitals, which occur in addition to the sigma bonds that are present in all hydrocarbons.

In contrast, saturated hydrocarbons only contain single bonds (sigma bonds), meaning they are fully “saturated” with hydrogen atoms and do not have any double or triple bonds. Therefore, the identification of unsaturated hydrocarbons hinges on recognizing the existence of these pi bonds.

Options that suggest the absence of carbon bonds or only the presence of triple bonds do not provide a comprehensive distinction for unsaturation. While triple bonds are indeed a feature of some unsaturated hydrocarbons, the presence of pi bonds (whether in double or triple bonds) is the critical factor for categorizing a hydrocarbon as unsaturated. Thus, identifying unsaturated hydrocarbons is fundamentally about detecting pi bonds in the structure.