- STRUCTURE OF CARBENE
- FORMATION OF CARBENES
- REACTIONS OF CARBENE
- Carbenes can defined as Neutral, Divalent carbon intermediate in which the carbon is covalently bonded to two atoms and two non – bonded orbital containing two electrons between them, they are highly reactive species.
- Carbenes are also called as methylenes, the Carbenes is electron deficient having only six-electrons in the outer shell of the carbon atom but posses no charge
- They are formed by homolytic fission like following type.
There are two possible kind of Carbenes
1.Singlet ( )
2.Triplet ( )
- In the singlet state a carbon atom in presumed to be approximate SP2 hybridization. Two SP2 hybrid orbital are utilized to form two covalent bonds where as the third hybrid contain unshared pair of electrons.
- The remaining P orbital remain vacant, thus singlet carbon resemble the structure of carbonium ion very closely, this state ha no magnetic moment.
- In the triple state a carbon is SP hybridized and it is linear or nearly linear species the two SP hybridized orbital are involved in the bond formation with the two groups while the two pure P orbitals ( Py & Pz ) lying perpendicular to each other .
- This non – bonding electron in Py & Pz have parallel spin.
FORMATION OF CARBENES
1. From cyclo elimination:
It is the reverse of cyclo addition reaction, the cleavage of a cyclic compounds in to various fragments.
E.g. The photochemical or thermal cleavage of cyclopropane gives Carbenes.
REACTIONS OF CARBENES
1.Cyclo addition reaction:
when a carbene added to alkene to form cyclopropane derivatives.
REIMER TIEMANN REACTION
The treatment of a phenol with chloroform and aq. NaOH at 600 followed by acidification, introduces a – CHO group in the aromatic ring mainly in ortho position to – OH group
The Wolff rearrangement consist in the conversion of an
α – diazoketone in to a ketene and nitrogen.
In the presence of water , alcohol, ammonia and amines, the ketene are converted in to corresponding derivatives.
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