Q3 · CSIR-NET Chemistry, December 2014
Paper: CSIR-NET December 2014 · Subject: Organic Chemistry · Chapter: General Organic Chemistry · Topic: Aromaticity · Marks: 2 · Difficulty: Medium
The compound that is antiaromatic is 
(I) (II) (III) (IV)
(I) (II) (III) (IV)(a)I
(b)II
(c)III
(d)IV
Answer
Answer: A ✓ checked by 4AB · confidence high
Explanation
Borole (I, C₄H₄BH) is a planar ring with an empty p orbital on boron. Its cyclic conjugation holds 4π electrons (4n, n = 1), so it is antiaromatic. Barrelene (II, bicyclo[2.2.2]octatriene) has only homoconjugated, non-cyclic π overlap, so it is non-aromatic. Cycloheptatriene (III) is interrupted by an sp³ CH₂, so it is non-aromatic. Cyclopropenone (IV) polarises to a 2π cyclopropenium ring, so it is aromatic. Answer: (a).
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