Which of the following compounds is nonaromatic?

• A. Furan
• B. Pyrrole
• C. $C_6{H}_6$ (benzene)
• D. Cyclohexane

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 requires having (4n + 2) π electrons, where n is a non-negative integer.
2. Analyze each compound: Furan and Pyrrole are five-membered heterocyclic rings with lone pairs contributing to the π system, making them aromatic. Benzene is a six-membered carbon ring with alternating double bonds, planar and fully conjugated, also aromatic.
3. Examine Cyclohexane: it is a six-membered ring but saturated (only single bonds), so it lacks a conjugated π electron system and is not planar in its typical chair conformation.
4. Since Cyclohexane does not have a continuous overlap of p orbitals and does not follow Hückel's rule, it is nonaromatic.
5. Therefore, identify Cyclohexane as the nonaromatic compound among the options.