Question:

Which one of the following is not aromatic?

Updated On: Apr 29, 2024
  • Cyclopentadienyl anion
  • Cycloheptatrienyl cation
  • Cyclooctatetraene
  • Thiophene
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The Correct Option is C

Solution and Explanation

Cyclooctatetraene is not aromatic in nature. In cyclooctatetraene, delocalisation of $ \pi - $ electrons takes place but Huckel's rule is not followed. According to Huckel's rule, it should contains $ 10\pi (4n+2) $ electrons but it contains only $ 8\pi $ electrons.
$ \pi $ electron $ (8)\ne (4n+2)=10 $ (i.e., Huckel rule is not followed), hence it is not aromatic.
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Concepts Used:

Hydrocarbons

Hydrocarbons can be described as organic compounds that consists only hydrogen and carbon atoms. These compounds are of different types and thereby have distinct natures. Hydrocarbons are colorless gases and are known for discharging faint odours. These have been categorized under four major classes named as alkynes, alkanes, alkenes, and aromatic hydrocarbons. 

Types of Hydrocarbons

  1. Saturated hydrocarbons - Saturated hydrocarbons are those compounds where there is a single bond exists between carbon atoms and are saturated with atoms of hydrogen.
  2. Unsaturated hydrocarbons - Hydrocarbons comprises of at least one double or triple bond between carbon atoms are known as unsaturated hydrocarbons.
  3. Aliphatic hydrocarbons - The term denotes the hydrocarbons formed as an outcome of the chemical degradation of fats. Aliphatic hydrocarbons are basically chemical compounds.
  4. Aromatic hydrocarbons - They are distinguished because of the presence of benzene rings in them. They give away distinct types of aroma. These hydrocarbons comprises of only hydrogen and carbon atoms.