In organic chemistry, what does an alkene's structure primarily feature?

Alkenes are a class of hydrocarbons characterized by the presence of at least one double bond between carbon atoms. This double bond consists of one sigma bond and one pi bond, which gives alkenes their unique chemical properties, such as reactivity compared to alkanes (which contain only single bonds). The presence of this double bond allows for different types of reactions, like addition reactions, where other atoms or groups can add across the double bond.

In contrast, hydrocarbons with only single bonds are called alkanes and do not exhibit the same reactivity, while rings of carbon atoms are typically associated with cycloalkenes or cycloalkanes, neither of which define alkenes in a broader sense. Additionally, triple bonds characterize alkynes, another class of hydrocarbons distinct from alkenes. Therefore, the defining feature of alkenes is this double bond, which is why the correct answer focuses specifically on this structural characteristic.