Editing Diene (section)

===Acidity===
The position adjacent to a double bond is [[acid]]ic because the resulting [[allyl]] anion is stabilized by resonance. This effect becomes more pronounced as more alkenes are involved to create greater stability. For example, deprotonation at position 3 of a 1,4-diene or position 5 of a 1,3-diene give a [[pentadienyl]] anion. An even greater effect is seen if the anion is aromatic, for example, deprotonation of [[cyclopentadiene]] to give the [[cyclopentadienyl anion]].<!-- TODO: chart of pKa for methylene in alkane, singly and doubly allylic, and Cp -->

[[File:HayashiChiralNBD.svg|thumb|left|122px|[[C2-Symmetric ligands|C<sub>2</sub>-symmetric]] diene ligand used in [[asymmetric catalysis]].<ref>{{cite journal|vauthors=Hayashi T, Ueyama K, Tokunaga N, Yoshida K|title=A Chiral Chelating Diene as a New Type of Chiral Ligand for Transition Metal Catalysts: Its Preparation and Use for the Rhodium-Catalyzed Asymmetric 1,4-Addition|journal=J. Am. Chem. Soc.|year=2003|volume=125|issue=38|pages=11508–11509|doi=10.1021/ja037367z|pmid=13129348}}</ref>]]