The correct stability order of the following species/molecules is:
General Organic Chemistry (GOC) · Class 11 · JEE Main Previous Year Question
The correct stability order of the following species/molecules is:
- a
- b
- c✓
- d
Step 1: Identify Each Species
- p (cyclopropyl anion): 3-membered ring with carbanion. 4 pi electrons in a 3-membered ring = antiaromatic. Highly unstable.
- q (cyclopentadienyl anion, ): 6 pi electrons (4n+2, n=1). Aromatic. Very stable.
- r (cyclooctatetraene): structural studies have shown that cyclooctatetraene is not
planar. It is most stable in a “tub” conformation, with poor overlap between adjacent
pi bonds. Stable but non-aromatic.
Step 2: Compare Stability
Order: (option c)
Key Points:
- Aromatic species (4n+2 pi electrons, cyclic, planar, conjugated) are extra stable
- Antiaromatic (4n pi electrons) are extra unstable
- Cyclopentadienyl anion and tropylium cation are the two classic aromatic ions
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