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← IIT-JEE 2008 · Paper 2
ChemistrySingle correct+3 / -1Question 45 of 66

IIT-JEE 2008 · Paper 2, Chemistry question 45

The correct stability order for the following species is

Four carbocations: (I) (CH₃)₂C⁺-O-CH₂CH₃ (tertiary, α-ethoxy); (II) CH₃CH⁺-CH₂-CH(CH₃)₂ (secondary alkyl); (III) CH₃CH⁺-O-CH(CH₃)₂ (secondary, α-isopropoxy); (IV) ⁺CH₂-CH₂-CH₂-CH(CH₃)₂ (primary alkyl).
Choose one option
Answer and worked solution

Official answer: D

Stabilising factors. An α-oxygen stabilises a carbocation strongly by +M donation (an oxocarbenium ion); alkyl groups stabilise by hyperconjugation and +I.

  • (I) tertiary and α-alkoxy: most stable.
  • (III) secondary and α-alkoxy.
  • (II) secondary alkyl.
  • (IV) primary alkyl: least stable.

(D) I > III > II > IV

Topics:Reactive intermediatesElectronic effects (inductive, resonance, hyperconjugation)
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