Cumulene
Cumulenes are hydrocarbons characterized by consecutive cumulated double bonds, in which several carbon–carbon π bonds occur in a row without intervening single bonds. The simplest cumulenes are allene (propadiene), H2C=C=CH2, and butatriene, H2C=C=C=CH2. These compounds are highly unsaturated and exhibit distinctive electronic and geometric properties compared with isolated double bonds.
Structure and geometry follow from the sp hybridization of the carbons involved in the double bonds. The
Examples and scope extend beyond allene and butatriene to longer chains with three or more consecutive C=C
Synthesis and reactivity: cumulenes are prepared by various methods, including dehydrohalogenation of vicinal dihalides and coupling
Applications and significance: cumulenes serve as building blocks in organic synthesis, serve as ligands in coordination