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ChemistryMediumClass 12
Reaction Intermediates — Carbocation, carbanion, free radical
GOC (General Organic Chemistry)
8
JEE Qs
8%
Hard
90
min
Always consider all possible electronic effects (Inductive, Resonance, Hyperconjugation) and carbocation rearrangements when predicting the stability and reactivity of these intermediates in mechanisms.
🧮 Key Formulas
Carbocation Stability Order (Alkyl, Inductive/Hyperconjugation): 3° > 2° > 1° > Methyl
Carbanion Stability Order (Alkyl, Inductive): Methyl > 1° > 2° > 3°
Free Radical Stability Order (Alkyl, Hyperconjugation): 3° > 2° > 1° > Methyl
Hybridization (Central Carbon): Carbocation/Free Radical = sp²; Carbanion = sp³ (unless resonance stabilized, then sp²)
Geometry (Central Carbon): Carbocation/Free Radical = Trigonal planar; Carbanion = Pyramidal (unless resonance stabilized, then planar)
✅ Key Points for JEE
- 1Mastering the relative stability order of carbocations, carbanions, and free radicals is crucial, as it dictates reaction pathways and product formation.
- 2Correctly applying electronic effects (Inductive effect, Resonance, Hyperconjugation) is paramount for determining and comparing the stability of these intermediates.
- 3Carbocations can undergo rearrangements (1,2-hydride, 1,2-alkyl, 1,2-phenyl shifts) to form more stable carbocations, which is a common trap in reaction mechanism problems.
- 4The geometry (e.g., trigonal planar for carbocations/free radicals, pyramidal for carbanions) and hybridization of the reactive carbon atom significantly influence reactivity and stereochemical outcomes.
- 5Resonance stabilization, when present, is a powerful effect that often overrides inductive and hyperconjugation effects, leading to exceptionally stable intermediates (e.g., allyl, benzyl carbocations/anions/radicals).
⚠️ Common Mistakes
- ✕Incorrectly ranking stability by considering only one electronic effect (e.g., only inductive) and ignoring resonance or hyperconjugation.
- ✕Failing to identify potential carbocation rearrangements, leading to incorrect major products in multi-step reactions.
- ✕Confusing the factors that stabilize carbocations with those that stabilize carbanions (e.g., electron-donating groups stabilize carbocations but destabilize carbanions).
- ✕Misidentifying the hybridization and geometry of the reactive center, especially in resonance-stabilized or strained systems.
NCERT Chapters
- Class 11 Chemistry Part II Ch 12: Organic Chemistry - Some Basic Principles and Techniques