00:01
So in this problem, we're asked to identify from a list of heterocycles, which are aromatic.
00:06
While i do not have the list, we can discuss what constitutes aromaticity in a heterocycle or in any molecule, for that matter.
00:14
So there are three things we are looking for for aromaticity.
00:18
One, is the molecule planar, which is most easily achieved via double bonds.
00:22
Two, is there a full delocalized ring or a full delocalized system? so is every atom in the compound have some form of delocalized electrons that can localize onto it? and three, the number of delocalized electrons has to be even, but not a multiple of four.
00:41
So in other words, it can be expressed by 4n plus 2.
00:44
This is known as huckle's rule.
00:45
So we might consider these three aromatic heterocycles as examples.
00:51
So in puridine, it looks like we might have eight electrons, which of course would break huckus rule.
00:58
But we have to decide whether those two electrons, that lone pair on the nitrogen, is localized or delocalized.
01:05
So for that, we have to look at resonance.
01:07
So we might draw a resonance structure where that delocalizes under the bond, the double bond adjacent, delocalizes adjacent, etc, all the way around.
01:19
And if we draw this resonant structure, we would have nitrogen with a double bond on it and a lone pair followed by a amount of other double bonds, and we realize we have the exact same compound.
01:37
It's still pyridine.
01:39
It's not a resonant structure of pyridine either, just a mirror image.
01:43
So that lone pair is localized.
01:46
So we have six electrons that are delocalized, so that may it just a chakos rule.
01:52
It is planar because it is benzene -like and has no extraneous items, and it is a full delocalized system.
01:59
So this is aromatic...