Methylene bridge

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The methylene bridge (methanediyl group) IUPAC methylene divalent group.png
The methylene bridge (methanediyl group)

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. It is the repeating unit in the skeleton of the unbranched alkanes.

Contents

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. [1]

A methylene bridge is often called a methylene group or simply methylene, as in "methylene chloride" (dichloromethane CH
2
Cl
2
). As a bridge in other compounds, for example in cyclic compounds, it is given the name methano. However, the term methylidene group (not to be confused with the term methylene group, nor the carbene methylidene) properly applies to the CH
2
group when it is connected to the rest of the molecule by a double bond (=CH2), giving it chemical properties very distinct from those of a bridging CH
2
group.

Reactions

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. [3]

Examples

Examples of compounds which contain methylene bridges include:

See also

Related Research Articles

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<span class="mw-page-title-main">Methylenedioxy</span> Functional group

Methylenedioxy is the term used in the field of chemistry, particularly in organic chemistry, for a functional group with the structural formula R-O-CH2-O-R' which is connected to the rest of a molecule by two chemical bonds. The methylenedioxy group consists of two oxygen atoms connected to a methylene bridge (-CH2- unit). The methylenedioxy group is generally found attached to an aromatic structure such as phenyl where it forms the methylenedioxyphenyl or benzodioxole functional group which is widely found in natural products, including safrole, and drugs and chemicals such as tadalafil, MDMA, paroxetine and piperonyl butoxide.

Methylene is an organic compound with the chemical formula CH
2
. It is a colourless gas that fluoresces in the mid-infrared range, and only persists in dilution, or as an adduct.

<span class="mw-page-title-main">Methylene group</span> Chemical group (–CH₂–)

A methylene 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 two single bonds. The group may be represented as −CH2 or >CH2, where the '>' denotes the two bonds.

In organic chemistry, a methylidyne group or just methylidyne is a neutral part of a molecule with formula ≡CH, consisting of a carbon atom bonded to a hydrogen atom by one single bond and to the rest of the molecule by one triple bond. For example, a methylidyne group is present in n-methylidyne-1-hexanaminium, H3C−(CH2)5−N+≡CH.

<span class="mw-page-title-main">Methylidene group</span> Chemical group (=CH₂)

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.

References

  1. W. A. Herrmann (1982), "The methylene bridge". In Advances in Organometallic Chemistry, volume 20, pages 195-197.
  2. "Active methylene compound".
  3. House, Herbert O. (1972). Modern Synthetic Reactions . Menlo Park, CA.: W. A. Benjamin. ISBN   0-8053-4501-9.