Pentadiene

These pentadiene derivatives are susceptible to lipid peroxidation, far moreso than monounsaturated or saturated fatty acids.

The basis for this reactivity is the weakness of doubly allylic C-H bonds, leading to pentadienyl radicals.

[8] Cyclooxygenases ("COX") are enzymes that generate prostanoids, including thromboxane and prostaglandins such as prostacyclin.

One practical consequence is that polyunsaturated fatty acids have poor shelf life owing to their tendency toward autoxidation, leading, in the case of edibles, to rancidification.

A number of complexes are known, including bis(pentadienyl) iron, Fe(C5H7)2, the "open" analog of ferrocene.

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.
Simplified chemical reactions associated with the formation of a hydroperoxide from a typical polyunsaturated fatty acid . In the second step, the hydroperoxide combines with another unsaturated side chain to generate a crosslink. [ 9 ]