Editing Structural isomer (section)

==Position isomerism (regioisomerism)<span class="anchor" id="Regioisomer"></span>==
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{{see also|Arene substitution pattern#Ortho, meta, and para substitution}}
'''Position isomers''' (also '''positional isomers''' or '''regioisomers''') are structural isomers that can be viewed as differing only on the position of a [[functional group]], [[substituent]], or some other feature on the same "parent" structure.<ref name=stok2015/>

For example, replacing one of the 12 hydrogen atoms –H by a [[Alcohol (chemistry)|hydroxyl]] group –OH on the [[pentane|''n''-pentane]] parent molecule can give any of three different position isomers:

{| align="center" class="skin-invert-image"
|-
| [[File:Pentan-1-ol-pos.png|180px]]
| [[File:Pentan-2-ol-pos.png|180px]]
| [[File:Pentan-3-ol-pos.png|180px]]
|-
| style="padding-left:20px;padding-right:20px;text-align:center;" | [[Pentan-1-ol]]
| style="padding-left:20px;padding-right:20px;text-align:center;" | [[Pentan-2-ol]]
| style="padding-left:20px;padding-right:20px;text-align:center;" | [[Pentan-3-ol]]
|}
Another example of regioisomers are [[α-Linolenic acid|α-linolenic]] and [[γ-linolenic acid]]s, both [[octadecatrienoic acid]]s, each of which has three double bonds, but on different positions along the chain.