Carbene - Carbene

Japanese: カルベン - かるべん（英語表記）carbene

A general term for intermediates with a divalent carbon bond and two active electrons _at the center, such as _CH2 : produced when ketene _CH2 =C=O or diazomethane _CH2N2 are photodecomposed. It is a highly reactive intermediate, and although it has been difficult to isolate it in _recent years, it has become possible to capture and observe it. There are carbenes with various substituents. For example, phenylcarbene _C6H5CH _: is produced from _{phenyldiazomethane} _C6H5CHN2 , and diphenylcarbene ( _C6H5 ₎ _2C _: is produced from _{diphenyldiazomethane} ( _C6H5 ) _2CN2 .

Carbenes can insert into carbon-hydrogen, nitrogen-hydrogen, or oxygen-hydrogen bonds and can add to carbon-carbon double bonds to form cyclopropane rings.

Carbenes include singlet carbenes, in which the two electron spins are paired, and triplet carbenes, in which the spins of the two electrons are not paired, and the latter exhibit radical properties. For example, the carbene of the following formula generated from a diazomethane derivative is yellow-orange in color and exists for a half-life of 19 minutes at room temperature.

The molecular structure of the carbene of the following formula trapped in the crystal has been analyzed.

Furthermore, when a large number of triplet carbenes are aligned in an orderly fashion, they exhibit ferromagnetic properties like iron.

[Tokumaru Katsumi]

[Reference] | Radical

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

ケテンCH₂＝C＝OやジアゾメタンCH₂N₂を光分解したときに生ずるCH₂:のように炭素中心が2価の結合をし、中心上に2個の活性な電子を有する中間体の総称。反応性の高い中間体であるが、近年その単離はしがたいものの、捕捉観測することができるようになった。各種の置換基をもつカルベンがある。たとえば、フェニルジアゾメタンC₆H₅CHN₂からはフェニルカルベンC₆H₅CH:が生じ、またジフェニルジアゾメタン(C₆H₅)₂CN₂からはジフェニルカルベン(C₆H₅)₂C:が生ずる。