Which of the following compounds would you expect to be antiaromatic?

• A. Pyrrole
• B. Cyclooctatetraene
• C. Cyclobutadiene
• D. Benzene

Answer: (C)

Verified step by step guidance

1. Step 1: Recall the definition of antiaromatic compounds. A compound is antiaromatic if it is cyclic, planar, fully conjugated (p orbitals overlapping continuously), and has 4n π electrons, where n is an integer (n = 1, 2, 3, ...).
2. Step 2: Analyze each compound for these criteria: pyrrole, cyclooctatetraene, cyclobutadiene, and benzene. Check if they are cyclic, planar, and fully conjugated, and count their π electrons.
3. Step 3: For cyclobutadiene, note that it is a 4-membered ring with 4 π electrons (4n, where n=1). It is planar and fully conjugated, which fits the antiaromatic criteria.
4. Step 4: For benzene, it has 6 π electrons (4n+2, n=1), is planar and fully conjugated, so it is aromatic, not antiaromatic.
5. Step 5: Pyrrole has 6 π electrons when counting the lone pair on nitrogen, making it aromatic. Cyclooctatetraene is not planar in its common conformation, so it is neither aromatic nor antiaromatic.