Methylene bridge
Inorganic chemistry,amethylene bridge,methylene spacer,ormethanediyl groupis any part of amoleculewith formula−CH2−;namely, acarbonatom bound to twohydrogenatoms and connected bysingle bondsto two other distinct atoms in the rest of the molecule. It is therepeating unitin the skeleton of the unbranchedalkanes.
A methylene bridge can also act as abidentateligandjoining two metals in acoordination compound,such astitaniumandaluminuminTebbe's reagent.[1]
A methylene bridge is often called amethylene groupor simplymethylene,as in "methylene chloride" (dichloromethaneCH
2Cl
2). As a bridge in other compounds, for example in cyclic compounds, it is given the namemethano.However, the termmethylidene group(not to be confused with the termmethylene group,nor thecarbenemethylidene) properly applies to theCH
2group when it is connected to the rest of the molecule by adouble bond(=CH2), giving it chemical properties very distinct from those of a bridgingCH
2group.
Reactions
[edit]Compounds possessing a methylene bridge located between two strongelectron withdrawing groups(such asnitro,carbonylornitrilegroups) are sometimes called active methylene compounds.[2]Treatment of these with strong bases can formenolatesorcarbanions,which are often used inorganic synthesis.Examples include theKnoevenagel condensationand themalonic ester synthesis.[3]
Examples
[edit]Examples of compounds which contain methylene bridges include:
See also
[edit]References
[edit]- ^W. A. Herrmann (1982), "The methylene bridge". InAdvances in Organometallic Chemistry,volume 20, pages 195-197.
- ^"Active methylene compound".
- ^House, Herbert O. (1972).Modern Synthetic Reactions.Menlo Park, CA.: W. A. Benjamin.ISBN0-8053-4501-9.