Gum Rosin acids are the complex mixture of several compounds, particularly abietic acid types and the pimaric acid types which belong to the diterpene group of organic compounds.
Abietic acid has conjugated double links and carboxyl groups. Pimaric acid is the dehydro form of abietic acid. Oxidation of abietic acid makes colophony more brittle and darker. The carboxyl group and double links in the acids can yield many kinds of salts and modified compounds for better purposes.