Explain why the following systems are not aromatic?
Solution and Explanation
(i)
For the given compound, the number of π-electrons is 6.
By Huckel’s rule,
4n + 2 = 6
4n = 4
n = 1
For a compound to be aromatic, the value of n must be an integer (n = 0, 1, 2…). Since the value of n is an integer.
Hence, the given compound is aromatic in nature.
(ii)
For the given compound, the number of π-electrons is 4.
By Huckel's rule,
4n + 2 = 4
4n = 2
n = \(\frac 12\)
For a compound to be aromatic, the value of n must be an integer (n = 0, 1, 2…), which is not true for the given compound.
Hence, it is not aromatic in nature.
(iii)
For the given compound, the number of π-electrons is 8.
By Huckel's rule,
4n + 2 = 8
4n = 6
n = \(\frac 32\)
For a compound to be aromatic, the value of n must be an integer (n = 0, 1, 2…). Since the value of n is not an integer.
Hence the given compound is not aromatic in nature.
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Concepts Used:
Aromatic hydrocarbon
Aromatic hydrocarbons, sometimes known as arenes, are aromatic organic molecules made up entirely of carbon and hydrogen. In aromatic compounds a benzene ring which is named after the simple aromatic chemical benzene, or a phenyl group when part of a larger structure, is the configuration of six carbon atoms.
Read More: Aromaticity
Reactions of Aromatic Hydrocarbons:
1. Aromatic Substitution Reactions
This reaction involves the replacement of one substituent on the ring of an aromatic hydrocarbon, commonly a hydrogen atom, by a different substituent group.
The common types of aromatic substitution reactions are:
- Nucleophilic aromatic substitution reactions
- Electrophilic aromatic substitution reactions
- Radical nucleophilic aromatic substitution reactions
2. Coupling Reactions
In these types of reactions, the coupling of two fragments that have a radical nature is achieved with the help of a metal catalyst