COMEDK2024ChemistryGeneral Organic ChemistryActual
Which of the following carbanions is the least stable?
Options
- ACH ₂= CHCH ₂⁻
- B( CH ₃ )₂ CH ⁻
- CC ₆ H ₅ CH ₂⁻
- DC ₆ H ₅⁻
Correct answer
B. ( CH ₃ )₂ CH ⁻
Step-by-step solution
Stability of carbanion depends on hybridization and resonance. CH₂ = CHCH₂^- : charge delocalized by resonance with double bond stable. C₆H₅CH₂^- : charge delocalized into benzene ring quite stable. C₆H₅^- : charge on sp^2 carbon higher s-character increases stability over sp^3 , but no delocalization into system. (CH₃)₂CH^- : charge on sp^3 carbon with two electron-donating -CH₃ groups, no resonance stabilization least stable.