Given the compound cyclobutadiene ($C_4{H}_4$), identify whether it is aromatic, anti-aromatic, or non-aromatic.

• A. Aromatic
• B. Non-aromatic
• C. Anti-aromatic

Answer: (C)

Verified step by step guidance

1. Step 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. Step 2: Analyze the structure of cyclobutadiene (C\\_4H\\_4). It is a four-membered ring with alternating double bonds, so it is cyclic and conjugated. Consider whether it is planar or not; cyclobutadiene is generally planar or nearly planar due to its small ring size.
3. Step 3: Count the number of π electrons in cyclobutadiene. Each double bond contributes 2 π electrons, so with two double bonds, the total is 4 π electrons.
4. Step 4: Apply Hückel's rule to the 4 π electrons. For n = 0, (4n + 2) = 2; for n = 1, (4n + 2) = 6. Since 4 π electrons do not fit the (4n + 2) rule but fit the 4n rule (4 × 1 = 4), the compound does not satisfy aromaticity but may be anti-aromatic if planar and conjugated.
5. Step 5: Conclude that cyclobutadiene is anti-aromatic because it is cyclic, planar, fully conjugated, and has 4 π electrons, which fits the 4n rule, leading to instability associated with anti-aromatic compounds.