A tertiary butyl carbocation is more stable than a secondary butyl carbocation because of which of the following?
- +R effect of -CH3 groups
- -R effect of -CH3 groups
- Hyperconjugation
- -I effect of -CH3 groups
Answer
(3) Hyperconjugation
Solution
tert-Butyl carbocation (CH3)3 C: 9 α-hydrogens ⇒ 9 hyperconjugative structures.
sec-Butyl carbocation CH3- CH-CH2-CH3: 5 α-hydrogens ⇒ 5 hyperconjugative structures.
As per NCERT, greater the number of alkyl groups (α-hydrogens) attached to the positively charged carbon, greater is the hyperconjugation and hence the stability of the carbocation.
-CH3 shows +I effect (not −I) and has no R effect.
Answer: (3)