There are seven structural isomers for n-butanol, or C4H10O: butan-1-ol, butan-2-ol, 2-methyl-propan-1-ol, 2-methyl-propan-2-ol, 1-methoxypropane, 1-methoxypropane and ethoxyethane. There are no double bonds, triple bonds or rings in any of these isomers.
Structural isomers, also known as constitutional isomers, represent all known and possible variations of a compound. All the isomers have the same molecular formula, but each has a different arrangement and bonding pattern. The chemical and physical properties of each isomer can also differ greatly. Sometimes structural formulas are simplified to form condensed structural formulas, in which the bonds to each carbon atom are omitted.
When referring to structural formulas of organic compounds, different groups of carbon atoms are distinguished by the number of other carbon atoms that each carbon is bonded to. A primary carbon is a carbon that is bonded to only one other carbon atom, a secondary carbon is a carbon atom that is bonded to two other carbon atoms, a tertiary carbon is bonded to three other carbon atoms, and a quaternary carbon is bonded to four other carbon atoms. These groups are denoted by a number with a degree symbol. For example, the primary carbon is represented by 1° and the secondary carbon is represented by 2°.