Ochem Help???

[Beagle]

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Can someone explain Huckal's rule to me?
I have no idea how to find out of a molecule is aromatic or not.
Kaplans book isn't of much help with this stuff(to me anyway)
Thanks !!!

 

[DesiDentist]

From my understanding you can use huckles rule if you see all of the aromatic compounds are cyclic (joined) and conjugated then you can use 4n+2 (Huckles rule) so if you had a benzene ring with 3 double bonds you know that those three double bonds have 6 e- so you can put the equation like this:

6=4n+2
-2 -2
________
4=4n

4/4 =n

n = 1

so benzene is aromatic since n= a whole number

If there was a cyclic compound with 8 e- or 4 double bonds then the equation would be:


8=4n+2
-2 -2
________

6=4n

6/4 =n which is not a whole number, thus not aromatic. But use huckles rule only after ruling out the first two criteria:

1.) cyclic
2.) conjugation

Hope this helps,

DesiDentist