Hey, guys, so now we're going to talk about another way to represent organic structures
and that's called the condensed structure.
The condensed method is a common way to describe the connectivity, connectivity – how a molecule
is connected, of a molecule using only text.
My speculation is that the logic behind this is that professors and chemists wanted a way
to represent these molecules using only a text editor.
Back in the day, there weren't these fancy drawing programs.
In fact, all they had was typewriters.
And they wanted some way to be able to notate what a molecule looked like without having
to draw fancy structures.
That's where they came upon the condensed structure.
Now, one thing that's important for this class is that you're going to have to really learn
how to interconvert between bondline and condensed very quickly.
The reason is because your professor, just to trick you, will use both structures interchangeably.
One question might be in bondline, another question might be in condensed.
Typically, just from my years of tutoring experience, I know that students really don't
like to think in condensed structure because it's kind of tricky.
So what I'm going to do today is I'm going to really show you how to interpret it.
So let's go ahead and look at – there's two different types.
Let's start off with the full condensed structure.
The full condensed structure is literally only text.
As you can see, we're taking a bondline structure and we're going to represent it in just only
one line of text.
Now a lot of this is straight forward meaning that you can see that this first CH3 here
is represented by that CH3 there.
Then you think, “Oh, this isn't so bad.”
The confusing part is that parentheses can be used to represent different things depending
on the subscripts in front of them.
Let's go ahead and look at that.
The first interesting parenthesis that you should know is this one that I've indicated
in blue which is a CH2 plus a subscript.
Notice that I have CH2 bracket 3.
What that means is that I have a repeating unit.
That's going to happen over and over and over again.
When I have CH2 with a 3 that doesn't mean I have 3 CH2's sticking out of one place.
What it means is I have 3 CH2's attached in order, like in a line.
Does that make sense so far?
The reason that saves us a lot of time is because some of these molecules can get really,
really long.
Imagine having a molecule that's 100 carbons long.
Do you want to write 100 CH2's?
No, it's way easier just to put CH2 in parenthesis with a 100 underneath it and that means I'm
going to repeat this unit 100 times.
Cool, so far?
Awesome.
So let's keep going.
Then we have this red one.
The red one is parenthesis alone.
If you have parenthesis alone, that indicates that you have a branch coming off of the chain.
Now, what's going to be interesting here is that sometimes this parenthesis is optional,
meaning that your professor may not always be so nice as to put that parenthesis there
to say that there's a branch.
Sometimes you're just going to have to know.
Alright, let's look at the logic here.
I have a carbon right here and that carbon is attached to two other things.
It's attached to one-half of the chain on the left and one-half of the chain on the
right.
By the way, this carbon, let's go ahead and locate it.
It's this one right here.
Let's just make sure that we know what we're talking about.
That carbon has a part of the chain on the left and a part of the chain on the right.
But it's also supposed to have two other things coming off of it because remember carbon wants
to have four bonds.
So what are those two other things?
Well, there's an H. That means that I have one H sticking off there.
And I also have an OH.
Now, notice that in this case I was nice and I put it in parenthesis.
What that meant was it's very easy to say, “Oh, the OH is the thing that's coming off
here.
Done.
I have my four bonds.”
Perfect.
But sometimes you might see it as just CHOH.
And then what you would need to know is that okay, one of them the H is going in one direction,
the OH is going in the other, but you know that both of them are attached to that carbon
because remember that that carbon needs four bonds.
That's kind of the way that we think about it.
You always think in terms of how can I make carbon have four bonds.
Finally, as you can see, there's one more type of parenthesis.
Sorry about getting a little sidetracked, but I wanted you guys to see an example of
that.
And then the last one is that if I have something else that's in parenthesis other than CH2
and it has a number in front of it.
So, in this case, I'm giving you CH3 with a 2 in the magenta brackets.
What that means is that these things are not attached in a line.
They're both attached to the same carbon.
Basically, the only time that I have things in a line repeating is if it's CH2.
That would mean that it would be linear.
So go ahead and write that down.
Linear meaning that it's all in one line.
But if I have two things that are not CH3 or three, right here, these would indicate
branching because of the fact that both of these CH3's must be coming off of one carbon
and what that would be is they would be attached to this one right here.
Now let's look at the logic with this one.
Let's look at this carbon.
Where is that carbon?
That carbon is right here.
That carbon needs to have four things attached to it.
Well, first of all, it has the whole left part of the chain, easy.
And then it has, let's look at it.
Let's see what's after the carbon.
After the carbon, I have an H and I have a CH3 and then I have another CH3 because it
says 2.
Those are the three other things that are attached to that carbon.
This would be bond two, bond three and bond four.
If you were to go ahead and draw that, you would see that I have an H here and then I
have CH3 here and then I have CH3 here.
Do you get that?
At the end of the day, the carbon still has four bonds, so it's fine.
But if you ever draw a structure, if you ever translate a structure that does not give carbon
four bonds, then you know you made a mistake.