Question

hybridisation of carbon in singlet carbene​

Answer 1

Explanation:

Carbenes

Carbenes

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Carbene

These are highly reactive neutral species containing a divalent carbon. It acts as reaction intermediate.In carbenes , carbon atom has four electrons in the valence shell of which two electrons are unshared.

Ex. – :CH2 (methylene carbene) , :CCl2 (dichlorocarbene)

:CH2 (methylene carbene) is parent carbene from which all other carbene compounds are derived.

Methods of preparation-

1) By thermal decomposition of diazo methane –

Methylene carbene is formed

CH2N2 ——— > :CH2 + N2

2) From halogen –

Carbene is formed by the alpha elimination of HX from haloform with base.

CHCl3 + B– ————> BH + :CCl2 (dichloro Carbene) + Cl–

3) By photochemical decomposition of ketene-

Carbene is formed.

CH2CO ———> :CH2 (Carbene) + CO

Structure –

Carbenes are classified as either SINGLET CARBENE & TRIPLET CARBENE.

SINGLET CARBENE-

In singlet state carbon atom is in sp2 hybridisation state. One of sp2 hybrid orbital contains unshared electron pair with opposite spins & two sp2 hybrid orbitals form two covalent bonds . The geometry is planar.There is no magnetic moment in this state.

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TRIPLET CARBENE –

In many triplet Carbene , carbon atom is in sp hybridization state. Two hybrid orbitals form sigma bond . Two remaining electrons with parallel spin occupy mutually perpendicular py & Pz orbitals. Geometry is linear . Such carbene would have magnetic moment.

Triplet carbenes are also known where carbon atom is in sp2 hybridisation state.Two nonbonding electrons occupy an sp2 atomic orbital & an unhybridized p-atomic orbital with parallel spin.Their geometry is bent .

source : OChemPal

Applications-

Carbene acts as reaction intermediate in so many organic reactions .

1) Carbyl amine reaction –

DichloroCarbene is reaction intermediate in this reaction.

RNH2 + CHCl3 + KOH (alc. ) ———–> RNC + 3KCl + 3 H2O

2) Reimer Tiemann reaction –

DichloroCarbene is reaction intermediate in this reaction .

3) Wittig reaction –

4) In the preparation of allenes-

Stability of Carbenes –

Carbenes in which the carbon of carbene is attached to two atoms , each bearing a lone pair of electron are more stable due to resonance.

Triplet Carbenes are more stable than singlet Carbene.