Which of the following compounds is aromatic?

• A. Cyclooctatetraene ($C_8{H}_8$)
• B. Cyclohexane ($C_6{H}_{12}$)
• C. Cyclobutadiene ($C_4{H}_4$)
• 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 meets these criteria. First, determine if the compound is cyclic and planar. For example, cyclohexane is cyclic but not planar and lacks conjugation, so it is not aromatic.
3. Count the number of π electrons in the ring for each compound. For example, cyclooctatetraene has 8 π electrons but adopts a non-planar 'tub' shape, preventing conjugation and aromaticity.
4. Apply Hückel's rule to the π electron count. For instance, cyclobutadiene has 4 π electrons, which fits the 4n rule (n=1) but not the (4n + 2) rule, making it antiaromatic or non-aromatic depending on geometry.
5. Identify benzene as the compound that is cyclic, planar, fully conjugated, and has 6 π electrons (n=1 in 4n + 2), satisfying all aromaticity criteria, making it aromatic.