Question

Consider the following compounds/species: 

The number of compounds/species which obey Huckel’s rule is ______.

• A. 6
• B. 2
• C. 5
• D. 4

Answer 1

The Correct Option is D

To determine which compounds obey Huckel's rule, we apply the rule for aromaticity. Huckel's rule states that a molecule is aromatic if it is planar, cyclic, completely conjugated, and has (4n + 2) π electrons, where n is a non-negative integer. We will analyze each given compound:

1. Compound 1: It must be cyclic and planar with conjugated π electrons. Count the π electrons; if the count follows (4n + 2), it is aromatic.
2. Compound 2: Check its cyclic structure, planarity, and conjugation. Count the number of π electrons to see if it satisfies the (4n + 2) rule.
3. Compound 3: Evaluate for cyclic nature, planarity, complete conjugation, and determine the number of π electrons for the Huckel's rule.
4. Compound 4: Similarly, check for cyclic, planar conjugated system and count the π electrons.
5. Compound 5: Assess the same properties as above for aromaticity.
6. Compound 6: Follow the same steps as for the others.

Verify which compounds meet the criteria of being cyclic, planar, fully conjugated, and having (4n + 2) π electrons. Upon detailed inspection, it is found that:

Compound	(4n + 2) π electrons satisfied
1	Yes
2	No
3	No
4	Yes
5	Yes
6	Yes

The molecules 1, 4, 5, and 6 satisfy Huckel's rule, making them aromatic compounds. Thus, the number of compounds/species which obey Huckel's rule is 4.