Answer
64.8k+ views
Hint: Aromatic and Anti-aromatic compounds can be differentiated on the basis of Huckel's Rule.
Complete step by step answer:
We can identify the and classify compounds as either aromatic or anti-aromatic based on the following rules:
1.For a compound to be Aromatic, the following conditions must be satisfied
-The compound should be cyclic
-The molecular geometry of the compound should be planar
-The compound should exhibit Resonance
-The compound should obey Huckle’s rule, and hence should have (4n+2) \[\pi \]electrons, where ‘n’ denotes the number of subsequent energy levels and can be equal to any whole number, i.e. 0,1,2,3,…
2.And for the compound to be Anti-Aromatic, the following conditions must be satisfied
-The compound should be cyclic
-The molecular geometry of the compound should be planar
-The compound should exhibit Resonance
-The compound should obey Huckle’s rule, and hence should have (4n) \[\pi \]electrons
3.If a compound does not have a continuous ring of conjugated p orbitals in a planar conformation, then it is nonaromatic
One important question you must be having is how we identify \[\pi \]electrons. For that, remember the following points. \[\pi \]electrons lie in p orbitals and \[s{p^2}\]hybridized orbitals, each have 1 p orbital. In a completely conjugated molecule, each carbon atom is \[s{p^2}\]hybridized, and hence the electrons present in these p orbitals are \[\pi \]electrons.
As for the compounds given to us,
![](https://www.vedantu.com/question-sets/3767aa4f-4296-4b4f-95b4-df08ec2e9c844973716594094517923.png)
Compound (I) satisfies the following conditions:
1.It is a cyclic compound
2.Its molecular geometry is planar
3.But it does not exhibit resonance
![](https://www.vedantu.com/question-sets/b5a0a00d-531d-40e6-9c84-e2d6b18361e3536011992315924947.png)
Shifting of electrons would bring us back to the same structure.
On the other hand, Compound (II) satisfies the following conditions:
1.It is a cyclic compound
2.Its molecular geometry is planar
3.It does exhibit resonance
![](https://www.vedantu.com/question-sets/72216db6-6d46-4974-80ef-56a29f12007c4562759697603148875.png)
This compound exhibits resonance in both directions.
And it has 4\[\pi \]electrons, which satisfies Huckle’s rule with the value of n=1.
Hence, we can conclude that Compound (I) is Non-Aromatic and Compound (II) is Anti-Aromatic.
-We know that, the trend in the stability of Aromatic, Non-Aromatic and Anti Aromatic compounds is:
Aromatic > Non-Aromatic > Anti-Aromatic
Hence, Anti aromatic compounds are less stable than Non-aromatic Compounds. This means that the conjugate bases of Anti aromatic compounds are more stable than Non-aromatic Compounds. And we know that the increasing stability of the conjugate base increases the acidity of the compound.
Hence Anti aromatic compounds are less acidic than Non-aromatic Compounds.
\[p{K_a}\] is a method used to indicate the strength of an acid. The lower the value of \[p{K_a}\], higher is the strength of the acid.
Now, relating the above conclusions to the given compounds, we get,
\[p{K_a}\] of Compound(I) < \[p{K_a}\]of Compound (II)
Hence, both the reason and assertion are true and are interdependent.
Option A is the correct
Note:
You should not fret over finding the value of ‘n’ in Huckle’s rule because ‘n’ is not a characteristic property of any molecule. It is merely a constant which can be substituted with any natural number to satisfy the Huckel's Rule.
Complete step by step answer:
We can identify the and classify compounds as either aromatic or anti-aromatic based on the following rules:
1.For a compound to be Aromatic, the following conditions must be satisfied
-The compound should be cyclic
-The molecular geometry of the compound should be planar
-The compound should exhibit Resonance
-The compound should obey Huckle’s rule, and hence should have (4n+2) \[\pi \]electrons, where ‘n’ denotes the number of subsequent energy levels and can be equal to any whole number, i.e. 0,1,2,3,…
2.And for the compound to be Anti-Aromatic, the following conditions must be satisfied
-The compound should be cyclic
-The molecular geometry of the compound should be planar
-The compound should exhibit Resonance
-The compound should obey Huckle’s rule, and hence should have (4n) \[\pi \]electrons
3.If a compound does not have a continuous ring of conjugated p orbitals in a planar conformation, then it is nonaromatic
One important question you must be having is how we identify \[\pi \]electrons. For that, remember the following points. \[\pi \]electrons lie in p orbitals and \[s{p^2}\]hybridized orbitals, each have 1 p orbital. In a completely conjugated molecule, each carbon atom is \[s{p^2}\]hybridized, and hence the electrons present in these p orbitals are \[\pi \]electrons.
As for the compounds given to us,
![](https://www.vedantu.com/question-sets/3767aa4f-4296-4b4f-95b4-df08ec2e9c844973716594094517923.png)
Compound (I) satisfies the following conditions:
1.It is a cyclic compound
2.Its molecular geometry is planar
3.But it does not exhibit resonance
![](https://www.vedantu.com/question-sets/b5a0a00d-531d-40e6-9c84-e2d6b18361e3536011992315924947.png)
Shifting of electrons would bring us back to the same structure.
On the other hand, Compound (II) satisfies the following conditions:
1.It is a cyclic compound
2.Its molecular geometry is planar
3.It does exhibit resonance
![](https://www.vedantu.com/question-sets/72216db6-6d46-4974-80ef-56a29f12007c4562759697603148875.png)
This compound exhibits resonance in both directions.
And it has 4\[\pi \]electrons, which satisfies Huckle’s rule with the value of n=1.
Hence, we can conclude that Compound (I) is Non-Aromatic and Compound (II) is Anti-Aromatic.
-We know that, the trend in the stability of Aromatic, Non-Aromatic and Anti Aromatic compounds is:
Aromatic > Non-Aromatic > Anti-Aromatic
Hence, Anti aromatic compounds are less stable than Non-aromatic Compounds. This means that the conjugate bases of Anti aromatic compounds are more stable than Non-aromatic Compounds. And we know that the increasing stability of the conjugate base increases the acidity of the compound.
Hence Anti aromatic compounds are less acidic than Non-aromatic Compounds.
\[p{K_a}\] is a method used to indicate the strength of an acid. The lower the value of \[p{K_a}\], higher is the strength of the acid.
Now, relating the above conclusions to the given compounds, we get,
\[p{K_a}\] of Compound(I) < \[p{K_a}\]of Compound (II)
Hence, both the reason and assertion are true and are interdependent.
Option A is the correct
Note:
You should not fret over finding the value of ‘n’ in Huckle’s rule because ‘n’ is not a characteristic property of any molecule. It is merely a constant which can be substituted with any natural number to satisfy the Huckel's Rule.
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