In addition reactions, a double or triple bond breaks and a group is added across the bond. What is the name of this type of reaction?

• A. Substitution reaction
• B. Addition reaction
• C. Combustion reaction
• D. Ester

Answer: (B)

Addition reactions occur when a double or triple bond breaks and a new group attaches across the carbons of that bond. The pi bond is opened up and two new sigma bonds form with the added atoms or groups, converting the unsaturated compound into a more saturated one. That’s why this type of reaction is called an addition reaction: you’re adding something across the bond rather than replacing an existing atom already attached to the carbon skeleton. For example, ethene can add hydrogen to form ethane, or add HCl to form chloroethane, or add water to form ethanol. In contrast, substitution reactions replace a substituent on a saturated carbon, combustion involves reacting with oxygen to form CO2 and H2O, and an ester refers to a functional group, not a reaction type.