Hckel

This forum made possible through the generous support of SDN members, donors, and sponsors. Thank you.
Get help with your application

Use all the free resources available to you from SDN: articles, guides, expert advising, forums discussions, and school research.

NonTraditional3

Full Member
10+ Year Member
Advertisement - Members don't see this ad
Can someone please explain what the "n" in 4n + 2 signifies? Does it mean # of pi electrons? # of pi bonds? # of sp2 hybridized atoms?
 
Can someone please explain what the "n" in 4n + 2 signifies? Does it mean # of pi electrons? # of pi bonds? # of sp2 hybridized atoms?

this is one of the conditions a molecule must satisfy to be considered aromatic. there is a specific number of electrons that the molecule must have to satisfy this equation where n can be 0,1,2,3,4....etc. it can only be a whole number. if it is not a whole number and the molecule satisfies all other conditions, then it is considered to be antiaromatic.

for example, you count the pi electrons in a molecule to be 12. it satisfies all other conditions (cyclic, conjugated etc).

4n+2=12
n=5/2; not a whole number, so the theoretical molecule would be antiaromatic.

however, if the pi electrons are 10 then

4n+2=10
n=2; the theoretical molecule is aromatic.
 
Advertisement - Members don't see this ad
So for benzene:

3 Pi Bonds = 6 pi e-

4n + 2 = 6

6 - 2 = 4

4/4 = n = 1

Whole number result for n, so benzene is aromatic....

yes, just make sure it meets all other conditions and this. n needs to be whole and is just some arbitrary number used in the equation and doesnt represent anything significant, that i know of.