Allene

An Allene is an hydrocarbon in which one atom of carbon is connected by double bonds with two other atoms of carbon. The simpliest allene is plopyl allene:

http://wiki.rozeta.com.pl/img/taw/allen_propylowy.png

Such pair of bonds make allene much more reactive than other alkenes. For example their reactivity with gaseous chlorine is more like reactivity of alkynes than other alkanes.