Vinylidene group

In chemistry, vinylidene means the divalent functional group =C=CH₂ (ethenylidene) or >C=CH₂ (1,1-ethenediyl), namely two carbon atoms connected to each other by a double bond, one of them bearing two hydrogens, and the other one connected to the rest of the molecule by a double bond or two single bonds.

Compounds containing this group (namely, with the general formula R=C=CH₂ or RR'C=CH₂) are called "vinylidenes". An example is 1,1-dichloroethene (CCl₂=CH₂) commonly called vinylidene chloride.

Vinylidene derivatives RR'C=CH₂ can be polymerized through the double C=C bond, yielding linear polymers (−CRR'−CH₂−)_n with single-bonded backbones. For example, vinylidene chloride yields the plastic polyvinylidene chloride (PVDC) (−CCl₂−CH₂−)_n. Likewise, vinylidene fluoride gives polyvinylidene fluoride (PVDF). Note that these vinylidene polymers are structurally different from those afforded by the vinylene derivatives, like polyvinylene fluoride from vinylene fluoride HFC=CHF. These polymers can be seen to include the vinyl derivatives as a special case where R' is hydrogen.

The group can exist all by itself as a very reactive metastable molecule methylidenecarbene (:C=CH₂), one of the carbenes.

See also

• vinylene group, −CH=CH−
• methylene group, =CH₂
• vinyl group, −CH=CH₂