Both naphthalene and azulene have 10 pie electrons and are aromatic. Pentalene is apparently antiaromatic and is unstable even at -100 degrees C. Heptalene has been made but it adds bromine, it reacts with acids, and it is not planar. Is Huckle's rule applicable to these compounds? If so, explain their lack of aromaticity.
Conjugated ring systems having 4n pi-electrons (e.g. 4, 8, 12 etc. electrons) not only fail to show any aromatic properties, but appear to be less stable and more reactive than expected. Planar bridged annulenes having 4n pi-electrons have ...
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