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JEE Main levelOne or more correct optionsDifficulty 2 of 3g1143

Which of the following are antiaromatic?

  1. Acyclobutadiene
  2. Bcyclopropenyl anion (cycloprop-2-en-1-ide)
  3. Ccyclopentadienyl cation (cyclopenta-2,4-dien-1-ylium)
  4. Dcyclopentadienyl anion (cyclopenta-2,4-dien-1-ide)

Answer: A, B, C

Each of the first three is planar, cyclic and conjugated with 4 pi electrons ( with ), so each is antiaromatic. The cyclopentadienyl anion has 6 pi electrons and is aromatic.
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