Isomers were introduced in Chapter 4. An isomer is a compound with the same formula as the “normal” compound, but a different structure. Isomer are sometimes referred to as branched compounds. Branching of a compound has the lowering the boiling point. In “Hydrocarbon families” section of Chapter 4, only the “iso” branch was discussed. With the hydrocarbon-derivative functional groups, there will also be an “iso” branch and, in addition, there will be secondary and tertiary branches.