Which type of reaction involves the addition of a carbon-carbon double bond?

An addition reaction is characterized by the process where atoms or groups of atoms are added to a molecule, specifically across a carbon-carbon double bond. In this reaction type, the double bond is broken, allowing for new atoms to bond to the carbon atoms that were originally involved in the double bond. This results in the conversion of alkenes (which contain carbon-carbon double bonds) into alkanes (which contain only single bonds and have the same number of carbon atoms).

For instance, when hydrogen gas adds across the double bond of an alkene, it results in the formation of an alkane through an addition reaction. This type of reaction is also fundamental in organic synthesis, facilitating the construction of more complex molecules from simpler ones.

The other types of reactions highlighted do not involve the addition to a double bond. Substitution reactions replace one atom or group in a molecule with another, elimination reactions typically involve the removal of small molecules (like water) to form double or triple bonds, and dehydration reactions involve the loss of water but do not specifically refer to the addition of molecules across a double bond.