Part A Aromaticity

It turns out that it is much faster to draw a solid-line circle so you will often see benzene drawn this way 

The heat of hydrogenation of benzene is actually -49kcal/mole. 

Model 2 Cyclic Conjugated n Systems ( Racetrack Analogy) 

Recall from ChemActivity 5 that an electron in a larger box has a longer wavelength and so is lower in potential energy than an electron confined to a smaller box.  

The racetrack analogy states that the electrons of benzene are low in P.E. because they reside in a box that is effectively very large due to the fact they can race endlessly around a track of conjugated p orbitals. We call this racetrack ofp orbitals a cyclic conjugated pi system. 

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S. Coffey, ed., Rodd s Chemistry of Carbon Compounds, 2nd ed., Vol. Ill, Part A, Aromatic Compounds, Elsevier Publishing Company, New York, 1971, p. 

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