Methylidene group
In organic chemistry, a methylidene group is any part of a molecule that consists of two hydrogen atoms bound to a carbon atom, which is connected to the remainder of the molecule by a double bond.[1] The group may be represented as =CH2, where the '=' denotes the double bond.
![](../I/Propene_Methylidene_Structural_Formulae_V.1.svg.png.webp)
This stands in contrast to methylene, the −CH2− group, which is connected to the rest of the molecule by two single bonds.[2] The distinction is often important, because the double bond is chemically different from two single bonds.
![](../I/Methylenecyclopropene.svg.png.webp)
The same name (methylidene) was used for the distinct molecule CH2, also known as carbene.[3] Formerly the methylene name was used for all three isomers (methylene, methylidene, and carbene).
Many organic compounds are named and classified as if they were the result of substituting a methylidene group for two adjacent hydrogen atoms of some parent molecule (even if they are not actually obtained that way). Thus, for example, methylenecyclopropene is named after cyclopropene.
References
- "methylidene (preferred IUPAC name)" (PDF). p. 314.
- "methylene (preferred IUPAC name)" (PDF). p. 58.
- "methylidene (preferred IUPAC name)" (PDF). p. 921.