NEETChemistryGeneral Organic Chemistry
Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): The carbocation ( CH ₃ )₃ C - C H - CH ₃ is less stable than CH ₃- C H - CH ₂- CH ₃ . Reason (R): The +I effect of a tert-butyl group is greater than that of an ethyl group. In the light of the above statements, choose the most appropriate answer from the options given below:
Options
- ABoth Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
- BBoth Assertion (A) and Reason (R) are true but Reason (R) is not the correct explanation of Assertion (A).
- CAssertion (A) is true but Reason (R) is false.
- DAssertion (A) is false but Reason (R) is true.
Correct answer
B. Both Assertion (A) and Reason (R) are true but Reason (R) is not the correct explanation of Assertion (A).
Step-by-step solution
Assertion (A) is true because the stability of alkyl carbocations is primarily determined by hyperconjugation, which depends on the number of -hydrogen atoms. The carbocation ( CH ₃ )₃ C - C H - CH ₃ has only 3 -hydrogens (from the right methyl group; the tert-butyl group has no -hydrogens). The carbocation CH ₃- C H - CH ₂- CH ₃ has 5 -hydrogens (3 from the left methyl group and 2 from the right methylene group). More -hydrogens result in more hyperconjugative structures, making the latter more stable. Reason (R)