Fundamentals of Organic ChemistryChemistryGeneral Organic Chemistry
Identify the more stable ion in each of the following pairs: Pair (a): (i) C ₆ H ₅- C H ₂ (ii) CH ₂= CH - C H ₂ Pair (b): (i) CH ₃- C H ₂ (ii) CH ₂= C H Pair (c): (i) (ii) Pair (d): (i) (ii)
Options
- Aa-(i), b-(i), c-(ii), d-(ii)
- Ba-(ii), b-(ii), c-(ii), d-(ii)
- Ca-(i), b-(i), c-(i), d-(i)
- Da-(ii), b-(ii), c-(i), d-(i)
Correct answer
A. a-(i), b-(i), c-(ii), d-(ii)
Step-by-step solution
In Pair (a), the benzyl carbocation (i) is more stable than the allyl carbocation (ii) due to more extensive resonance delocalization of the positive charge over the benzene ring. In Pair (b), the ethyl carbocation (i) is more stable than the vinyl carbocation (ii). In the vinyl carbocation, the positive charge resides on a more electronegative sp -hybridized carbon, making it highly unstable. The ethyl carbocation is stabilized by hyperconjugation. In Pair (c), ion (ii) is an allylic carbocation, which is stabiliz