Amethylene groupis any part of a molecule that consists of twohydrogenatomsboundto acarbonatom, which is connected to the remainder of the molecule by twosingle bonds.[1]The group may be represented as−CH2−or>CH2,where the '>' denotes the two bonds.
This stands in contrast to a situation where the carbon atom is bound to the rest of the molecule by adouble bond,which is preferably called amethylidene group,represented=CH2.[2]Formerly the methylene name was used for both isomers. The name “methylene bridge“can be used for the single-bonded isomer, to emphatically exclude methylidene. The distinction is often important, because the double bond is chemically different from two single bonds.
The methylene group should be distinguished from theCH2molecule calledcarbene.[3]This was also formerly calledmethylene.
Activated methylene
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The central carbon in1,3-dicarbonyl compoundis known as anactivated methylenegroup. This is because, owing to the structure, the carbon is especially acidic and can easily be deprotonated to form a methylene group.[4]
See also
editReferences
edit- ^"methylene (preferred IUPAC name"(PDF).
- ^"methylidene (preferred IUPAC name"(PDF).
- ^IUPAC,Compendium of Chemical Terminology,2nd ed. (the "Gold Book" ) (1997). Online corrected version: (2006–) "carbenes".doi:10.1351/goldbook.C00806
- ^"Active Methylenes".
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