Allenes

In organic chemistry, allenes are organic compounds in which one carbon atom has double bonds with each of its two adjacent carbon atoms (R₂C=C=CR₂, where R is H or some organyl group). Allenes are classified as cumulated dienes. The parent compound of this class is propadiene (H₂C=C=CH₂), which is itself also called allene. An group of the structure R₂C=C=CR− is called allenyl, where R is H or some alkyl group. Compounds with an allene-type structure but with more than three carbon atoms are members of a larger class of compounds called cumulenes with X=C=Y bonding.