What structural feature characterizes unsaturated molecules?

Unsaturated molecules are characterized by the presence of one or more double or triple bonds between carbon atoms. This structural feature allows them to have fewer hydrogen atoms than their saturated counterparts, which only contain single bonds.

Double bonds consist of one sigma bond and one pi bond, while triple bonds consist of one sigma bond and two pi bonds. These bonds introduce rigidity and affect the reactivity of the molecules, making unsaturated compounds generally more reactive than saturated ones. For example, alkenes (which have at least one double bond) and alkynes (which have at least one triple bond) demonstrate this enhanced reactivity, as they can participate in addition reactions.

The presence of either double or triple bonds is what defines unsaturation, making the choice that encompasses both types of bonds the most accurate description of unsaturated molecules. This indicates that a molecule can be unsaturated due to either of these structural features, thereby reinforcing the characterization of unsaturation in organic chemistry.