Q.What are Carbocations and Carbanions? How are they generated? Explain the relative stability of alkyl carbocations and carbanions. OR Write IUPAC names of the following compounds:

Carbocations (electron-deficient, sp2, positively charged carbon) are stabilized by more alkyl groups (3 degree most stable), while carbanions (electron-rich, sp3, negatively charged carbon) are destabilized by alkyl groups (methyl most stable) -- the two stability orders are exact opposites.

Carbocations: a carbocation is a reactive intermediate species in which a carbon atom bears a positive charge and has only six electrons in its valence shell (an incomplete octet), making it electron deficient. The positively-charged carbon is sp2 hybridized, with the three sigma bonds arranged in a trigonal planar geometry, and an empty, unhybridized p orbital perpendicular to this plane. Carbocations are generated by heterolytic cleavage (heterolysis) of a covalent bond to carbon, in which the other atom/group (the leaving group) takes away both electrons of the shared pair, leaving the carbon short of one electron pair. Example: (CH3)3C-Br -> (CH3)3C+ + Br- (Br takes both bonding electrons, leaving a tertiary carbocation).

Carbanions: a carbanion is a reactive intermediate in which a carbon atom bears a negative charge, having a complete octet made up of three bond pairs and one lone pair. The negatively-charged carbon is sp3 hybridized, with a pyramidal shape (similar to ammonia), the lone pair occupying one of the four sp3 positions. Carbanions are generated by heterolytic cleavage of a covalent bond to carbon in which carbon itself retains both electrons of the shared pair. Example: R3C-H + strong base (B-) -> R3C:- + HB (the base removes the proton, and carbon keeps both bonding electrons as a lone pair).

Relative stability of alkyl carbocations: 3 degree (tertiary) > 2 degree (secondary) > 1 degree (primary) > methyl. This order arises because alkyl groups are electron-releasing (+I inductive effect) and can also stabilize the adjacent positive charge through hyperconjugation (donation of electron density from adjacent C-H sigma bonds into the empty p orbital). The more alkyl groups attached to the positively-charged carbon, the more this electron density is pushed towards/delocalized onto it, reducing (stabilizing) the electron deficiency -- so a tertiary carbocation (3 alkyl groups) is most stable, and the methyl cation (no alkyl groups, no such stabilization) is least stable.

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