Question

What are the different types of carbenes?
A. Singlet
B. Triplet
C. Both of the above
D. None of the above

Answer 1

Carbenes are generally represented as ${{:C}}{{{H}}_{{2}}}$ which are neutral divalent carbon species having two unshared valence electrons. If all the electrons are spin paired they are called as singlet and if there is an unpaired set of electron spin they are considered as triplet.

Complete step by step answer:
Carbenes ${{:C}}{{{H}}_{{2}}}$ are highly unstable, highly reactive, and are neutral species; Carbenes are good electrophiles because it is ${{6}}{{{e}}^{{ - }}}$ species. It tries to attain octet structure thus striving to get electrons.
Some of the methods of preparation of carbenes include
Photolysis or pyrolysis of ${{C}}{{{H}}_{{2}}}{{{N}}_{{2}}}$
${{C}}{{{H}}_{{2}}}{{{N}}_{{2}}}\xrightarrow[{}]{{{\Delta }}}{{:C}}{{{H}}_{{2}}}{{ + }}{{{N}}_{{2}}}$
From halogen
${{CHC}}{{{l}}_{{3}}}{{ + }}{{{B}}^{{ - }}}\xrightarrow{{}}{{BH + :CC}}{{{l}}_{{2}}}$
${{\alpha }}$elimination of ${{HX}}$by base results in the formation of Carbene
Carbene can also be formed by photochemical decomposition of ketene
${{C}}{{{H}}_{{2}}}{{CO}}\xrightarrow{{}}{{:C}}{{{H}}_{{2}}}{{ + CO}}$
Carbenes are of two types
Singlet and triplet
In singlet carbene it is believed as ${{s}}{{{p}}^{{2}}}$ hybridised and has got a planar geometry and triplet carbene is ${{sp}}$ hybridised with linear geometry. Triplet carbene has a bond angle of ${{18}}{{{0}}^{{o}}}$ and singlet carbene has got a bond angle of ${{10}}{{{3}}^{{o}}}$. Triplet carbene is also called biradical. Singlet carbene is diamagnetic in nature with antiparallel spin. Triplet carbene is paramagnetic with the same spin.

The, correct answer is C.

Additional information:
Carbene finds many applications such as it can act as reaction intermediate in organic reactions such as
In carbylamine reaction, Reimer Tiemann reaction, Wittig reaction and also in the preparation of allenes
In carbenes the carbon is attached to two atoms each having a lone pair of electrons is more stable because of resonance. The metal complexes in organometallic species with a formula ${{{L}}_{{n}}}{{MCR}}{{{R}}^{{`}}}$are given as carbene complexes.

Note: In singlet the bond angle is ${{10}}{{{3}}^{{o}}}$and there is more repulsion and thus there will be increase in energy and thus there will be decrease in stability. In case of triplet carbene the bond angle is ${{18}}{{{0}}^{{o}}}$and has a more open structure and repulsion is minimum thus the energy is less and the stability is high. Thus triplet carbene is more stable than singlet carbene.