Hey guys!
Let’s look at this last section dealing with the fourth type of hydrocarbon – aromatic
hydrocarbons.
Here we're going to say aromatic compounds have a benzene ring in common.
That's their major feature.
Remember, a benzene ring is C6H6 because remember, every corner and edge is a carbon which I've
displayed here.
What we need to realize here is that you can draw it a bunch of different ways.
We're going to say here maybe the double bond is here, here and here.
We're going to say that these double bonds overlap or they're alternating actually.
Alternating will be a more correct term for them.
These double bonds alternate.
They go double bond, single bond, double bond.
We're going to say that alternating double and single bonds they actually have a name
in organic.
It's called conjugation.
Here's the thing about conjugation.
If you can draw them alternating, that means you can draw them in different ways.
We could draw the double bonds in that orientation or maybe the double bonds go this way.
Both are possible structures.
Because we are just moving around double bonds or moving around electrons, we’re
going to say these two initial drawings represent the resonance structures of benzene.
Here's the thing.
Resonance structures are imaginary.
They're not real.
The real structure is called the resonance hybrid.
It is basically a composite of both of these structures on top of each other.
Basically think of it as they both have blueprints to the inside of a building.
One alone doesn't have all the information you need.
What happens here is you take one blueprint and you put the other one on top
and the composite is them lining up everything on top of each other and then you’ll get
the complete picture of the building itself.
That complete picture represents my resonance hybrid.
Here's the thing.
Anywhere a double bond has been will get a dotted line.
There was a double bond here, so this is going to get a dotted line.
There was a double bond here so this is going to get a dotted line.
Double bond here so it's going to get a dotted line.
Basically anywhere a double bond has been is going to get a dotted line.
That represents my resonance hybrid.
You may eventually see benzene written like this, not like those two resonance structures
but instead you'll see a circle.
That circle represents the resonance hybrid.
Again, why is it a circle?
Because the double bonds have been everywhere inside of that compound based on those two
resonance structures.
We just used a circle to show this.
Me drawing these dotted lines where double bonds have been is basically me giving you
the groundwork to draw this at the end.
This also represents the resonance hybrid.
They're both the same exact structure.
Here, benzenes can be found in everyday compounds from the gasoline that we drive, fossil fuels
from oil rigs.
There's a lot of places that you'll find benzene, even when we're breaking down fossil fuels
and burning them.
Some of the by-products are benzene.
We're going to stay here even in some vital medications that people use every day, you
can find benzene involved.
Here for example, this molecule, huge molecule, I've highlighted in red the benzene ring.
Right here is one benzene.
Here's another benzene and here’s a third benzene.
This is an incredibly important drug.
This is Lipitor.
For those people with high cholesterol, they use Lipitor to help control that.
It controls your cholesterol.
It controls the fat within your body.
Everyday things from the fossil fuels that we use to drive machines around this world
to even Lipitor that people get from the counter at the pharmacy.
All of them have benzene involved.
Benzene is an incredibly versatile on compound.
It's incredibly stable that's what you find it in a lot of different things.
If you want to take Organic 2 eventually, you're going to realize that when you get
to Organic 2, there are actually a few chapters entirely devoted to just benzene and compounds
just like benzene, aromatic compounds.
They're incredibly important in synthesis of a lot of other things so that's why so
much detail is paid attention to them.
But for right now, just remember the basics in terms of it.
It's C6H6.
It has resonance structures but the resonance hybrid is the better example of what it looks
like.
Later on, we'll go over some of the reactions that benzenes commonly do but nothing too
extravagant.
Again, we're holding off a lot until you get to Organic 2.