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Hydrocarbons

Long Answer Type

211.

What are the characteristics of a compound to be aromatic?
Or
What do you mean by aromaticity?
Or
What are the necessary conditions for any system to be aromatic?

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212.
Write a short note on annulenes.

Annulenes are monocyclic conjugated polyenes which contain an even number of carbon atoms in their molecules. These are represented by the general formula (-CH = CH-)_n where n = 2, 3, 4.....

Aromatic nature in annulenes: According to Huckel’s rule, annulenes containing (4n + 2) electrons and having a coplanar cyclic carbon skeleton should be aromatic in nature. For example,

(i) [4] Annulene. It is non-aromatic because it does not contain  electrons.

(ii) [6] Annulene. It is aromatic because it contains  electrons.

(iii) [8] Annulene. It is non-aromatic because it does not contain  electrons.