{{Short description|Organic compound (CH2(CH)3CH2, charge –1, 0, or 1))}}

In [[organic chemistry]], '''pentadienyl''' refers to the organic [[radical (chemistry)|radical]], anion, or cation with the formula {{chem2|[CH2(CH)3CH2]^{''z''} }}, where ''z'' = 0, −1, +1, respectively.

==Organometallic chemistry==

In [[organometallic chemistry]], the '''pentadienyl anion''' is a ligand, the acyclic analogue of the more-common [[cyclopentadienyl anion]]. The pentadienyl anion is generated by [[deprotonation]] of [[pentadiene]]. A number of complexes are known, including bis(pentadienyl) iron, {{chem2|Fe(C5H7)2}}, the "open" analog of [[ferrocene]]. Only few pentadienyl complexes feature simple {{chem2|C5H7}} ligands. More common is the dimethyl derivative 2,4-{{chem2|Me2C5H5}}. Additionally, many pentadienyl ligands are cyclic, being derived from the addition of hydride to ''η''⁶-arene complexes or hydride abstraction from [[cyclohexadiene]] complexes.<ref>{{cite journal|authors=Lothar Stahl, Richard D. Ernst|title=Pentadienyl Complexes of the Group 4 Transition Metals|journal=Advances in Organometallic Chemistry|volume=55|year=2007|pages=137–199|doi=10.1016/S0065-3055(07)55003-3|isbn=9780123739780 }}</ref><ref>{{cite journal|author=Richard D. Ernst|title=Structural and reactivity patterns in transition-metal-pentadienyl chemistry|journal=Chem. Rev.|year=1988|volume=88|issue=7 |pages=1255–1291|doi=10.1021/cr00089a013}}</ref>

The first pentadienyl complex to be reported was derived from protonolysis of a complex of pentadienol:<ref>{{cite journal|title=Pentadienyl and Hexadienyl Carbonium Ions as Ligands in Stable Complex Cations|authors=Mahler, J. E.; Pettit, R.|journal=J. Am. Chem. Soc.|year=1962|volume=84|issue=8 |pages=1511–1512|doi=10.1021/ja00867a051}}</ref>

:<chem>Fe(C5H7OH)(CO)3 + H+ -> [Fe(C5H7)(CO)3]+ + H2O</chem>

Treatment of this cation with [[sodium borohydride]] gives the pentadiene complex:

:<chem>[Fe(C5H7)(CO)3]+ + H- -> Fe(C5H8)(CO)3</chem>

==Organic chemistry==

In organic chemistry, the '''pentadienyl radical''', {{chem|C|5|H|7|•}}, is of some significance as an especially stabilized radical. The radical is delocalized over five carbon centers. Consequently the C−H bond in the diene (C''H''₂(CH=CH₂)) is especially weak. Fats derivatives containing this "doubly [[allylic]]" group are collectively called [[drying oil]]s. They tend to polymerize in a useful way upon exposure to air.

:[[File:ModelDryingOil.png|thumb|300px|right|Representative triglyceride found in a drying oil. The two upper fatty esters display high reactivity toward air owing to their tendency to form pentadienyl and heptadienyl radicals, respectively.]]

==Biochemistry==

[[Cyclooxygenase]]s ("COX") are [[enzyme]]s that generate [[prostanoid]]s, including [[thromboxane]] and [[prostaglandin]]s such as [[prostacyclin]]. [[Aspirin]] and [[ibuprofen]] exert their effects through inhibition of COX.

[[File:PGG2 mechanism.png|thumb|left| Mechanism of COX activation and catalysis. The tyrosyl radical can abstracts the 13-pro(''S'') hydrogen of [[arachidonic acid]] to generate a pentadienyl radical, initiating the COX cycle.]]

==References==

{{Reflist}}

[[Category:Anions]]

[[Category:Free radicals]]