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.

The blue part of this diagram of a propene molecule is a methylidene group.

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.

3-Methylidenecycloprop-1-ene is named as a cyclopropene with a methylidene substituent.

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.

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