Question 1

Why is a carbocation carbon trigonal planar?

Accepted Answer

A classical carbocation carbon is sp2-hybridized. Its three sigma bonds lie in one plane with 120-degree separation, while an empty unhybridised p orbital is perpendicular to that plane.

Question 2

What happens during a 1,2-hydride shift?

Accepted Answer

A hydrogen on the carbon adjacent to the carbocation migrates to the carbocation carbon with the electron pair of its C-H bond. The positive charge is transferred to the adjacent carbon, while the carbon skeleton and total number of carbon atoms remain unchanged.

Question 3

What happens during a 1,2-alkyl shift?

Accepted Answer

A carbon substituent on the adjacent carbon migrates to the carbocation centre with the electron pair of its C-C bond. A new C-C bond forms and the positive charge remains on the carbon from which the substituent migrated.

Question 4

Does every carbocation undergo rearrangement?

Accepted Answer

No. A rearrangement is favoured when a neighbouring migration produces a more stable carbocation pathway. The presence of a vacant p orbital allows such rearrangement chemistry, but it does not mean that every neighbouring group must migrate.

Question 5

What is the general stability order of simple alkyl carbocations?

Accepted Answer

The general order is methyl < primary < secondary < tertiary. Alkyl groups increase carbocation stability through their electron-donating inductive effect and through hyperconjugation.

Carbocation Rearrangement: A Better Place for the Positive Charge

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