text: Carbon–carbon bond-forming reactions are organic reactions in which a new carbon–carbon bond is formed. They are important in the production of many human-made chemicals such as pharmaceuticals and plastics. The reverse reaction, where a carbon-carbon bond is broken, is known as carbon-carbon bond activation.
  Some examples of reactions which form carbon–carbon bonds are the aldol reaction, Diels–Alder reaction, Grignard reaction, cross-coupling reactions, the Michael reaction and the Wittig reaction.
  The directed synthesis of desired three-dimensional structures for tertiary carbons was largely solved during the late 20th century, but the same ability to direct quaternary carbon synthesis did not start to emerge until the first decade of the 21st century.