What are carbene ? | Reaction intermediates

It is a very short living Species formed in between the reaction

Carbene is a molecule containing neutral carbon atom with valence of two and two unshared electrons ( loan pair ).

The general formula is
R’ – (:C) – R or  R=C:

Where R is any alkyl group or substituted Hydrogen atoms.

Methylene

The term Carbene is refer to the specific compound H2C and it also known as methylene group.This is the parent hydride from this only all other carbenes are derived.

It is neutral molecule and having six electrons in outer shell of carbon atom,it makes the molecule into electron deficient.

Since Carbene are having two Odd electrons.It can classified into two types,

Types of Carbene :-

•  Singlet Carbene :

Singlet carbene are spin paired having opposite spin.

These are generally sp² hybridized

Shape is Bent

Bond angle is 103°

Bond length is 112 pm.

Spin State = (2S+1), S for singlet carbene is zero as the electrons are antiparallel.

Spin state = (2×0+1) = 1

•  Triplet Carbene :

Triplet carbene having two unpaired electrons, they are present in two different Orbitals and possess same spin.

They present as either sp or sp² hybridized and shape is linear or bent

Bond angle is 180°

Bond length is 103 pm

Spin state = (2S+1), S for triplet carbene is 1 both electrons are having same spin. So therefore

Spin state = (2×1+1) = 3.

Note : Most of the carbene are have non-linear triplet state expect those with Nitrogen,Oxygen,Sulfur and Halide atoms directly bonded with divalent carbon.

How they differentiate Carbenes :-

Carbenes are called as Singlet carbene and Triplet Carbene depending upon the electronic spin nature of the two unshared electrons.

The Triplet Carbenes are paramagnetic and they can be identified by the Electron Spin resonance Spectroscopy 

Why triplet carbene are more stable than singlet carbene ?

Triplet carbene has lesser energy when it compared with singlet carbene. This is because in singlet carbene there is more electronic repulsion between those two unshared electrons which is present in the same orbital. But in triplet carbene those two unshared electrons are present in the two different orbitals.

So the triplet Carbene is more stable than Singlet Carbene.

Well,Yes