Aromaticity question...

[predentn]

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There's a question in the O. Chem Odyssey about which compound will react faster under SN1 conditions...one of the choices was chlorobenzene which was incorrect. Can someone explain why the dechlorinated chlorobenzene (benzene with a positive charge) is not aromatic?

 

[levyusupov]

chlorobenzene is an aryl group that is very unreactive from the reason that benzene ring with + charge is VERY unstable because its disobey the rule of 4n+2 (Huckle's rule) for aromaticity. thus, rings with 2(n=0),6(n=1), 10(n=2) electrons will be aromatic, and rings with4, 5, 6 electrons - like positively charged benzene (5 electrons) - will not be aromatic.

if ypu study with the deatroyer this concept is clearly explained.

check this link for more info:

http://en.wikipedia.org/wiki/H%C3%BCckel's_rule

GOOD LUCK !!!!

 

[Saber tooth]

There's a question in the O. Chem Odyssey about which compound will react faster under SN1 conditions...one of the choices was chlorobenzene which was incorrect. Can someone explain why the dechlorinated chlorobenzene (benzene with a positive charge) is not aromatic?

chlorobenzen (when it's benzene with a postive charge does not have a P orbital at every carbon on the ring plus it doesn't follow 4n+2 rule therefore its not aromatic (decreasing ring stabliazation)