Benzene is described as aromatic because it
- A. has a pleasant smell
- B. contains only carbon and hydrogen
- C. reacts readily by addition
- D. is planar, cyclic and has a delocalised system of six pi electrons obeying Huckel's rule
Explanation
Aromaticity in the modern sense requires a planar cyclic conjugated system containing 4n plus 2 pi electrons, which for benzene means six, and this confers exceptional stability. The word originally referred to the smell of such compounds, which is why the first option is the historical but chemically wrong answer. Aromatic compounds characteristically undergo substitution rather than addition.
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