Question

Explain the formation, stability and geometry of the following reaction intermediates: carbanion, carbene and free radicals.

Answer 1

Hint: We can say that a carbanion is an anion where the carbon has the ability to three bonds and a formal negative charge is present in the carbon atom. We can say that a carbene is a chemical species that has a neutral atom of carbon exhibiting two as its valency and two unshared outermost electrons. We can say that free radicals are those atoms which consist of an unpaired electron.

Complete answer:
We could define carbanion as an anion where carbon would form three bonds which means the carbon is trivalent and a formal negative charge is present in the carbon. We can say that the conjugate base of a carbon acid is a carbanion. We can write the chemical reaction as,
${R_3}CH + :{B^ - } \to {R_3}C{:^ - } + HB$
Formation: We can say that the formation of carbanion is from deprotonation of alkanes, deprotonation of alkenes, deprotonation of arenes, deprotonation of alkynes and they are called as alkyl, alkenyl, aryl, and acetylide anions respectively. We can say the carbanion is formed by heterolytic fissions. The compound which has an active hydrogen atom that reacts with base and carbanion is formed.
Stability: We can classify carbanion into three types: Primary carbanion, Secondary carbanion, Tertiary carbanion. When the +I effect is greater, the stability of carbanion would be lesser. We can give the relative order of stability among carbanion is,
${\text{Primary > Secondary > Tertiary}}$
Geometry: We can say that in carbanion, the atom of carbon is $s{p^3}$ hybridized. We can say that the geometry is pyramidal.
We can say that the carbene is a molecule which has a neutral atom of carbon that has valency of two and two unshared outermost electrons. We can write the general formula of carbene as $R = C:$, here substituents (or) hydrogen atoms are R.
Formation: We can say that formation of carbene is by the photolysis of aliphatic diazo compounds (or) ketones.
Stability: We can say that there are two forms of carbene: Singlet carbene and triplet carbene. We have to know that carbenes are extremely reactive whereas singlet state is taken as less stable.
Geometry: We can say that hybridization of carbon in singlet state of carbene is $s{p^2}$. We can say that the bond angle is $120^\circ $ and the trigonal planar is the geometry. The hybridization of carbon in the triplet state of carbene is $sp$. We can say that the bond angle is $180^\circ $ and linear is the geometry.
Formation: We can say that the formation of free radicals takes place by homolytic fission.
Stability: We can classify free radicals as primary free radicals, secondary free radicals, and tertiary free radicals. We have to know the tertiary alkyl free radicals contain most stability because of the more +I effect. When the +I effect is greater, the stability of free radicals would be greater.
Geometry: In alkyl free radicals, the carbon is $s{p^2}$ hybridized. We have to know that the bond angle is $120^\circ $ and the geometry is trigonal planar.

Note:
We can also say that carbene may also indicate a particular compound known as methylene $\left( {C{H_2}} \right)$. We can say that classification of carbene is based on electronic structure. We can say in carbanion, the electron density concentration is when the negatively charged carbon reacts with several electrophiles that have different strengths.