CAIE A-Level Chemistry 14.2.5 Carbocation Stability and Markovnikov Addition

Practise using positive inductive effects to compare carbocations and explain the major product of HX addition.

Exam points

rank tertiary, secondary and primary carbocations by the number of electron-releasing alkyl groups
explain greater stability by positive inductive donation of electron density towards C+
choose the major HX-addition product formed through the more stable carbocation intermediate

[Maximum number: 2]

Allyl chloride is an important chemical used in the manufacture of plastics, pharmaceuticals and pesticides.

allyl chloride

2-bromo-1-chloropropane, $\mathrm{CH}_{3} \mathrm{CHBrCH}_{2} \mathrm{Cl}$ , is the major product of the reaction of allyl chloride with HBr .

Figure for Question 14.2.5—Inductive effects of alkyl groups question 1 — CAIE A-Level Chemistry AS

Explain why 2-bromo-1-chloropropane is the major product of this reaction.

M1 major product formed from more stable intermediate / carbocation

OR

(intermediate has) $2^{\circ}$ carbocation which is (more) stable

M2 (positive) inductive effect / (+)I of alkyl groups (on the intermediate)

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14.2.5—Inductive effects of alkyl groups question 1