Which of the following compounds is aromatic?

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

Answer: (A)

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 determine if it is cyclic and planar. Benzene (C\6H\6) is a well-known planar cyclic compound with alternating double bonds, making it fully conjugated.
3. Count the number of π electrons in each compound. For benzene, there are 6 π electrons (from three double bonds). For cyclohexane (C\6H\12), there are no double bonds, so no π electrons. Cyclobutadiene (C\4H\4) has 4 π electrons, and cyclooctatetraene (C\8H\8) has 8 π electrons.
4. Apply Hückel's rule to each compound: benzene has 6 π electrons, which fits 4n + 2 when n = 1, so it is aromatic. Cyclobutadiene with 4 π electrons fits 4n (n=1), which is antiaromatic if planar. Cyclooctatetraene with 8 π electrons fits 4n (n=2), typically non-aromatic because it is not planar.
5. Conclude that benzene is aromatic because it meets all criteria, while the others are either non-aromatic or antiaromatic due to their electron count and/or geometry.