Question

What is the stability of carbanion$?$

Answer 1

Hint: The stability of an ion whether a cation or anion is determined by the hindrance around it. In the case of organic compounds, the stability of carbon ions is determined by the inductive effect. A carbanion is an ion of carbon that has a negative charge on it.

Complete answer:
A carbanion is the ion of carbon that has accepted an electron thus having a negative charge on it. It is represented as ${C^ - }$. When such an ion is attached to a carbon chain then the stability is determined by the inductive effect. Inductive effect is the electronic effect which means in this effect there is a tendency of electrons releasing and electron-accepting by the functional groups. If a functional group is not present in the carbon chain then by the concept of hyperconjugation, other chain members can donate electron pairs. Inductive effect is of two types:
${\text{ 1}}{\text{. }} - I$Effect
$2.{\text{ + I}}$ Effect
In the case of the negative inductive effect, it means it helps in accepting the electrons. Whereas in positive inductive effect it shows that it helps in releasing of electrons. Since there is a negative charge on carbon ions which makes it unstable since a carbon having four valence electrons is more stable than having five valence electrons. Therefore ${C^ - }$is unstable. Therefore it is needed that it should be hindered less by other groups. Thus a carbanion having the least number of its substituents is most stable. We can also say that the degree of carbanion must be small. If the degree of carbon is large then due to steric hindrance and the inductive effect it makes it unstable.
Thus order of stability of carbanion is based on degree of carbon:
${1^ \circ }{\text{ }} \succ {\text{ }}{{\text{2}}^ \circ }{\text{ }} \succ {\text{ }}{{\text{3}}^ \circ }$ Decreasing order of stability of carbanion.

Note:
Thus the stability of carbanion is based on the degree of the carbanion. The degree of carbon means the number of groups attached to that carbon only. If we say it is a ${3^ \circ }$ carbon then three groups are attached to that single carbon atom. The larger the degree of carbon, the more will be the inductive effect.