Wiktionary
propadiene
n. (context organic compound English) the simplest allene, CH2=C=CH2
Wikipedia
Propadiene
Propadiene is the organic compound with the formula HC=C=CH. It is the simplest allene or compound with two adjacent C=C double bonds, and can also be identified as allene. As a constituent of MAPP gas, it has been used as a fuel for specialized welding.