Carbenes (H2C) are neutral and reactive species that have six electrons in the outer shell of carbon, making them electron deficient. Since carbenes are species having two odd electrons, we can classify carbenes based on their spin states.
Singlet Carbene
The electrons are present in different orbitals with opposite spins. The electrons are paired in sp2 hybridized orbitals and behave as paired electrons.
Spin state= (2S + 1), S for singlet carbene is zero, as the electrons are antiparallel.
Therefore, spin state = (2 × 0 + 1) = 1
Triplet Carbene
Both electrons are present in different orbitals, and they possess the same spin.
Spin state = (2S + 1), S for triplet carbene is 1, as both electrons have the same spin.
Therefore, spin state= (2 × 1 + 1) = 3
Hybridization of Singlet and Triplet Carbene
Singlet carbene hybridization: They are sp2 hybridized with a bent shape. They have a bond angle of 103° and a bond length of 112 pm.
Hybridization of Singlet Carbene
Triplet carbene hybridization: They possess a sp hybrid orbital with a linear shape. They have a bond angle and bond length of 180° and 103 pm, respectively.
Why Is Triplet Carbene More Stable than Singlet?
Triplet carbene has lower energy than singlet carbene because, in singlet carbene, there are more inter-electronic repulsions as both the electrons exist in the same orbital, whereas in triplet carbene, the two electrons exist in different orbitals, making it possess less energy.
What Are Free Radicals?
Free radicals in organic chemistry are formed by the homolytic cleavage of carbon bonds. The shape of the species formed is planar, and the carbon is sp3 hybridized with an odd electron being placed in the p-orbital. If the free radical is relatively stable, then it may possess a planar structure.
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