Illustrated Glossary of Organic Chemistry

Allene: A molecule having two carbon-carbon double bonds that share a single sp carbon. Also refers to propadiene (H₂C=C=CH₂), the parent member of this series.

Molecular Structure of Allene
Note the perpendicular pi bonds, and perpendicular terminal methylene groups.

Lewis structure		Ball and spoke		Space-filling model		Molecular model kit

2,3-Pentadiene, a typical allene