propa-1,2-diene Allene 12075-35-3 463-49-0 6688-91-1 60731-10-4 HSDB 5135 05675_FLUKA Tricarbon PROPADIENE 294985_ALDRICH Propadienylidene 1,2-Propadiene Dimethylenemethane CH2=C=CH2 CHEBI:37601 Propadiene, inhibited [UN2200] [Flammable gas] Sym-allylene UN2200 Carbon trimer EINECS 207-335-3 InChI=1/C3H4/c1-3-2/h1-2H