Does Resonance Always Stabilize a Molecule

Delocalized n systems must be planar, or nearly so, for resonance stabilization to be most effective. Imposing planarity, however, may cause ring strain. 

Examine the geometry of planar corannulene. Are all of its six-membered rings the same If so, draw a Lewis structure whieh best represents the molecule. If not, draw one or more Lewis structures as appropriate. 

Aeeording to your Lewis structure(s) and to the actual geometry of the molecule, is the bonding in planar corannulene fully delocalized (as in benzene), or are some CC bonds long and some short Do your results support the notion that planar corrannulene is resonance stabilized Explain. 

Buckminsterfullerene (Cm or Buckyball ) is structurally related to corannulene. In which molecule would you expect 7U-orbital overlap be more effective Explain. How many chemically unique carbons are there in C6o Measure CC bond distances. How many unique distances are there Is each benzene fully delocalized or is one resonance contributor more important than the other  

Hiickel s rule states that planar cyclic 71 systems involving 4n+2 electrons will be unusually stable ( aromatic ), while cyclic 7i systems with 4n electrons will be unstable ( antiaromatic ). 

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