Question

The central C-atom of a carbanion possesses?
A) Sextet of electrons
B) Octet of electrons
C) Duplet of electrons
D) None of these

Answer 1

Hint: The carbanions are produced when the carbon and the bond between the removal groups undergo the heterolytic bond fission such that carbon acquires the two electrons from the bonding pair. It has six electrons from the covalent bonds. Thus there is a total of eight electrons associated with the central carbon atom.

Complete step by step answer:
The anions are the species that carries the negative charge. Carbanions are also the anion carrying a negative charge.
The carbanions are generated by the removal of the group which is attached to the carbon without removing its bonding electrons. In other words, heterolytic or uneven cleavage of bond where the carbon atom and the group shared the pair of electron.
Such that the group leaves without its electron and acquires the positive charge, while the carbon atoms hold on both of the electrons from the bond. Because of this carbon atom carries both unshared electron and as well as the negative charge.

The heterolytic bond cleavage is as shown:
\[\begin{align}
  & \text{ }{{\text{R}}_{\text{2}}}\text{ }{{\text{R}}_{\text{2}}}\text{ } \\
 & \text{ }\!\!|\!\!\text{ }\!\!|\!\!\text{ } \\
 & {{\text{R}}_{\text{1}}}\begin{matrix}
   \text{-} & \text{C} & \text{-} \\
\end{matrix}\text{Z}\xrightarrow[\text{-}{{\text{Z}}^{\oplus }}]{\text{Heterolytic bond cleavage}}{{\text{R}}_{\text{1}}}\begin{matrix}
   \text{-} & \text{C} & {}^{^{-}}\bullet \\
\end{matrix}\text{ }\bullet \text{ } \\
 & \text{ }\!\!|\!\!\text{ }\!\!|\!\!\text{ } \\
 & \text{ }{{\text{R}}_{\text{3}}}\text{ }{{\text{R}}_{\text{3}}} \\
 & \text{ } \\
\end{align}\]
Therefore, the carbon atom carries six electrons from the three covalent bonds \[\text{C-}{{\text{R}}_{\text{1}}}\]\[\text{ C-}{{\text{R}}_{2}}\]and \[\text{C-}{{\text{R}}_{3}}\] two electrons from the lone pair of electrons. Thus carbon has a total of eight electrons. Therefore, the octet of the carbon atom is complete. The basic example of the simplest carbanion is $\text{C}{{\text{H}}_{\text{3}}}^{\text{-}}$which methyl carbanion. It is a carbanion of methane$\text{C}{{\text{H}}_{\text{4}}}$.

Hence, (B) is the correct option.

Additional information:
Feature of carbanion:
1) Simple carbanion like $\text{C}{{\text{H}}_{\text{3}}}^{\text{-}}$ is isoelectronic with the\[\overset{\text{}}{\mathop{\text{N}}}\,{{\text{H}}_{\text{3}}}\]. The carbanion species are $\text{s}{{\text{p}}^{\text{3}}}$hybridized. The shape of the carbanion is pyramidal. The structure of carbanion is as follows:

2) Carbanions are good nucleophiles. They carry the negative charge hence attack the electrophilic species.
3) The carbanion is chiral when all the substituents on the carbon are different .here the lone pair of the carbon acts as one of the substituents on the chiral carbon.
4) A carbanion is base. They can abstract the acidic proton easily. Thus they have wide applications in various reactions. For example in Michael addition is the reaction the carbanion with the $\text{ }\!\!\alpha\!\!\text{ , }\!\!\beta\!\!\text{ -}$unsaturated carbonyl compound

Note: The carbanion possess the $\text{s}{{\text{p}}^{\text{3}}}$hybridization. It should be tetrahedral geometry. However there is non- bonded pair of electron-bonded pair repulsion $\text{(LP-BP)}$which pushes the bond to form a pyramidal geometry as seen in ammonia \[\overset{\text{}}{\mathop{\text{N}}}\,{{\text{H}}_{\text{3}}}\].