Question

Among the following :

The set which represents aromatic species is

• A. I, II and III
• B. III, IV and V
• C. II and III
• D. I, II and IV

Answer 1

The Correct Option is D

Aromaticity is determined based on Hückel's Rule, which states that a molecule is aromatic if it: 

• is planar, cyclic, and conjugated.
• has \(4n + 2\) π electrons (where \( n = 0,1,2,3, \dots \)).

Analyzing the given species:

1. Structure I: Aromatic (benzene-like), planar cyclic conjugated system with 6 π electrons (\(4(1) + 2 = 6\)), satisfies Hückel's rule.
2. Structure II: Aromatic, typically represents a planar cyclic conjugated ion (e.g., cyclopentadienyl anion) with 6 π electrons, satisfies Hückel's rule.
3. Structure III: Non-aromatic or antiaromatic (doesn't fulfill Hückel's rule, usually due to non-planarity or not having \(4n+2\) electrons).
4. Structure IV: Aromatic (likely represents tropylium ion, cycloheptatrienyl cation), planar cyclic conjugated system with 6 π electrons (\(4(1) + 2 = 6\)), satisfies Hückel's rule.
5. Structure V: Non-aromatic or antiaromatic, does not fulfill the aromaticity criteria.

Conclusion:

The species that satisfy all conditions for aromaticity (planar, cyclic, conjugated, and having \(4n + 2\) π electrons) are structures I, II, and IV.

Therefore, the correct answer is Option (D): I, II and IV.

Answer 2

To determine which of the following species are aromatic, we must apply Hückel's rule, which states that a molecule is aromatic if it is cyclic, planar, fully conjugated, and has 4n + 2 π-electrons, where n is a non-negative integer.

I: This is a benzene ring (C₆H₆), which is aromatic. It is cyclic, planar, fully conjugated, and has 6 π-electrons (n = 1).
II: This is cycloheptatrienyl cation (C₇H₇⁺), which is aromatic. It has 6 π-electrons (n = 1) and is planar and conjugated.
III: This is a benzene ring with a single bond (C₆H₆), which is not aromatic because the conjugation is disrupted by the single bond.
IV: This is a cyclopropenyl cation (C₃H₃⁺), which is aromatic. It has 4 π-electrons (n = 1) and is planar and conjugated.
V: This is a cyclohexane ring, which is not aromatic because it does not have a conjugated π-system.

Thus, the aromatic species are I, II, and IV.

Hence, the correct answer is (D) I, II, and IV.