Which of the following compounds is aromatic?

• A. Cyclooctatetraene ($C_8{H}_8$)
• B. Cyclobutadiene ($C_4{H}_4$)
• C. Cyclohexane ($C_6{H}_{12}$)
• D. Benzene ($C_6{H}_6$)

Answer: (D)

Verified step by step guidance

1. Recall the criteria for aromaticity: a compound must be cyclic, planar, fully conjugated (p orbitals at every atom in the ring), and follow Hückel's rule, which states it must have (4n + 2) π electrons, where n is a non-negative integer (0, 1, 2, ...).
2. Analyze each compound to check if it is cyclic and planar. For example, cyclohexane is cyclic but not planar and lacks conjugation, so it cannot be aromatic.
3. Count the number of π electrons in the ring for each compound. Only π electrons in conjugated double bonds or lone pairs that participate in conjugation count. For instance, benzene has 6 π electrons from three double bonds.
4. Apply Hückel's rule to the π electron count. If the number of π electrons fits the formula (4n + 2), the compound is aromatic. For example, benzene with 6 π electrons fits when n=1.
5. Confirm that the compound is fully conjugated and planar to allow continuous overlap of p orbitals, which stabilizes the aromatic system. Benzene meets all these criteria, making it aromatic.