Editing Pyrethroid (section)

==Chemistry and classification==
[[File:(R,R)-(+)-trans-chrysanthemic acid.svg|thumb|(1''R'',3''R'')- or (+)-trans-[[chrysanthemic acid]].]]
Pyrethroids are classified based on their mechanism of biological action, as they do not share a common chemical structure. Many are 2,2-dimethylcyclopropanecarboxylic acid derivatives, like [[chrysanthemic acid]], [[ester]]ified with an [[Alcohol (chemistry)|alcohol]]. However, the [[cyclopropyl]] ring does not occur in all pyrethroids. [[Fenvalerate]], which was developed in 1972, is one such example and was the first commercialized pyrethroid without that group. 

Pyrethroids which lack an α-cyano group are often classified as ''type I pyrethroids'' and those with it are called ''type II pyrethroids''. Pyrethroids that have a common name starting with "cy" have a cyano group and are type II. Fenvalerate also contains an α-[[cyano group]].

Some pyrethroids, like [[etofenprox]], also lack the ester bond found in most other pyrethroids and have an [[ether]] bond in its place. [[Silafluofen]] is also classified as a pyrethroid and has a [[silicon]] atom in the place of the ester. Pyrethroids often have [[chiral centers]] and only certain stereoisomers work efficiently as [[insecticide]]s.<ref>{{Cite journal|last=Ujihara|first=K|date=2019|title=The history of extensive structural modifications of pyrethroids|journal=[[Journal of Pesticide Science]]|volume=44|issue=4|pages=215–224|doi=10.1584/jpestics.D19-102|pmc=6861428|pmid=31777441}}</ref>