The Criteria for Aromaticity—Huckels Rule

This behavior is characteristic of aromatic compounds. The structural features that distinguish aromatic compounds from the rest are discussed in Section 17.7. 

Problem 17.9 Compounds A and B are both hydrogenated to methylcyclohexane. Which compound has the larger heat of hydrogenation Which compound is more stable  

Four structural criteria must be satisfied for a compound to be aromatic  

The p orbitals on all six carbons of benzene continuously overlap, so benzene is aromatic. 1,3,5-Hexatriene has six p orbitals, too, but the two on the terminal carbons cannot overlap with each other, so 1,3,5-hexatriene is not aromatic. 

Every p orbital overlaps with two neighboring p orbitals. 

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