Methylene bridge

In organic chemistry, a methylene bridge, methylene spacer, or methanediyl group is any part of a molecule with formula −CH2−; namely, a carbon atom bound to two hydrogen atoms and connected by single bonds to two other distinct atoms in the rest of the molecule.

A methylene bridge can also act as a bidentate ligand joining two metals in a coordination compound, such as titanium and aluminum in Tebbe's reagent.

Compounds possessing a methylene bridge located between two strong electron withdrawing groups (such as nitro, carbonyl or nitrile groups) are sometimes called active methylene compounds.

[2] Treatment of these with strong bases can form enolates or carbanions, which are often used in organic synthesis.

Examples include the Knoevenagel condensation and the malonic ester synthesis.