What is an alkene?

An alkene is defined as a hydrocarbon that contains at least one double bond between carbon atoms. This characteristic double bond is what sets alkenes apart from other types of hydrocarbons. The presence of a double bond leads to a different set of chemical properties compared to alkanes, which contain only single bonds and are considered saturated hydrocarbons.

Alkenes are also unsaturated hydrocarbons because they can react with additional hydrogen atoms to become saturated; this is a key reaction that showcases their chemical reactivity. Common examples of alkenes include ethene (ethylene) and propene, both of which feature carbon-carbon double bonds that are fundamental to their structure and behavior in chemical reactions.

In contrast, the other classifications mentioned do not accurately describe alkenes. Hydrocarbons without double or triple bonds refer to alkanes, while saturated hydrocarbons pertain specifically to alkanes as well. Aromatic compounds, on the other hand, are characterized by their cyclic structures and delocalized π electrons, which is distinct from the properties of alkenes. Thus, the correct option focuses on the essential nature of alkenes in organic chemistry—their defining feature of containing a double bond between carbon atoms.