Carbon–carbon bond formation with enols/enolates Carbon–carbon bond formation with enols/enolates (A) Resonance structures of an enolate illustrating that there is high electron density on both the oxygen atom and one of the carbon atoms in this molecule. (B) When an enolate attacks a carbonyl group through its nucleophilic carbon, a new carbon–carbon bond is formed. If there is a good leaving group, X, on the tetrahedral intermediate species then a second carbonyl group can form, otherwise the tetrahedral species can gain a proton to form an alcohol. (C) The reaction of dihydroxyacetone phosphate (red) and glyceraldehyde-3-phosphate (blue) to form fructose-1,6-bisphosphate is a key reaction in glucose synthesis, while the reverse reaction occurs in the breakdown of glucose (glycolysis). Amanda L. Jonsson et al. Essays Biochem. 2017;61:401-427 ©2017 by Portland Press Ltd