Given below are two statements: one is labelled as Assertion A and, the other is labelled as Reason R.
Assertion A: [6] Annulene, [8] Annulene and cis-[10] Annulene, are respectively aromatic, not-aromatic and aromatic.
Reason R: Planarity is one, of the requirements of aromatic systems.
In the light of the above statements, choose the most appropriate answer from the options given below.
Assertion A: [6] Annulene, [8] Annulene and cis-[10] Annulene, are respectively aromatic, not-aromatic and aromatic.
Reason R: Planarity is one, of the requirements of aromatic systems.
In the light of the above statements, choose the most appropriate answer from the options given below.
- Both A and R are correct and R is the correct explanation of A
- Both A and R are correct but R is NOT the correct explanation of A.
- A is correct but R is not correct.
- A is not correct but R is correct.
The Correct Option is D
Solution and Explanation
To determine the correct answer to the question, let's examine both the assertion and the reason provided:
Assertion A: [6] Annulene, [8] Annulene, and cis-[10] Annulene, are respectively aromatic, non-aromatic, and aromatic.
Reason R: Planarity is one of the requirements of aromatic systems.
- Analyzing Assertion A:
- [6] Annulene: This molecule is aromatic because it satisfies the Huckel's rule for aromaticity, which requires the molecule to have \(4n+2\) π electrons, where \(n\) is a non-negative integer. Here, for [6] annulene, \(n=1\) (as it has \(4(1)+2 = 6\) π electrons).
- [8] Annulene: This molecule is non-aromatic. According to Huckel's rule, it would require 10 π electrons to be aromatic, but it only has 8, which does not satisfy the rule.
- cis-[10] Annulene: This molecule is also non-aromatic because it cannot maintain planarity due to angle strain and steric hindrance. Although it has 10 π electrons, its inability to be planar disqualifies it as aromatic.
- Analyzing Reason R:
Planarity is indeed one of the critical requirements for a compound to exhibit aromaticity. Aromatic compounds must have a cyclic, continuous overlap of p orbitals, which is only possible if the molecule is planar.
- Conclusion: Since Assertion A is incorrect but Reason R is correct, the correct option is: A is not correct but R is correct.
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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