Methylidene

The blue part of this diagram of a propene molecule is a 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. The group may be represented as CH₂=, where the '=' denotes the double bond.

This stands in contrast to methylene, also called methylene bridge, i.e. the −CH₂− group, which is connected to the rest of the molecule by two single bonds. 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 methylene group should be distinguished from the compound carbene, which is a molecule unto itself, with the formula CH
₂. 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.

See also

• Methylene
• Methyl group
• Methine