Huckel's rule

[wait4me]

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I am very confused about Huckel's rule. How do you know whether to count the lone pair electrons or not??

It is starting to confuse me and make me forget whats sp2 and sp3. Do electrons count for sp2 and sp3.

 

[loveoforganic]

The general most basic rule is that if the atom connected to the lone pair is taking part in a pi bond, then the lone pair is not in a p orbital.

 

[maverick09]

this is how i learned it. if you have a heterocyclic compound (for example with an oxygen atom) and an atom has two lone pairs, then the first lone pair can donate into the system and the second loan pair cannot. this would make the oxygen atom sp2. a general rule of thumb (i was told) is that if you have a lone pair of electrons on an atom in a ring and the atom is not already involved in a pi bond (as loveoforganic said) then the lone pair can delocalize into the system

 

[wait4me]

The general most basic rule is that if the atom connected to the lone pair is taking part in a pi bond, then the lone pair is not in a p orbital.

so if an oxygen or sulfur does not have a pi bond near it, but has 2 lone pairs of electrons, would those both be counted?

 

[maverick09]

if an oxygen or sulfur has two lone pairs on it and has no attached pi bond then only one of the loan pairs can be counted, not both

 

[Omni]

The way I was told to do it is that you count up 2n+2 pi electrons.
If there are lone pairs available, include them only if it adds up to 2n+2, otherwise don't.

 

[POWP]

doubt this is still tested on the mcat?

 

[loveoforganic]

The way I was told to do it is that you count up 2n+2 pi electrons.
If there are lone pairs available, include them only if it adds up to 2n+2, otherwise don't.

That's technically correct. A molecule will do essentially whatever it can to avoid antiaromaticity, and changing the hybridization of a lone pair is pretty easy. Cyclobutadiene is actually nonaromatic because it stretches two of its bonds to avoid conjugation.