in chemistry, and in organic chemistry, in particular, is

この命名法に法則が

just the notation and the nomenclature or the naming

これはメタン、こっちはプロパン。

that we use.

これはメタン。

And what I want to do here in this video and really the next

そしてプロパンにはより簡単な表し方がある。

few videos is to just make sure we have a firm grounding

である。

in the notation and in the nomenclature or how we name

とても困難なのは、

things, and then everything else will

化学の復習として、

hopefully not be too difficult.

最初に、基本的な

So just to start off, and this is really a little bit of

有機化合物の命名

review of regular chemistry, if I just have a chain of

有機化学で

carbons, and organic chemistry is dealing

表れることが見えてくる。

with chains of carbons.

Let me just draw a one-carbon chain, so it's really kind of

ridiculous to call it a chain, but if we have one carbon over

here and it has four valence electrons, it

wants to get to eight.

That's the magic number we learned in

just regular chemistry.

For all molecules, that's the stable valence structure, I

guess you could say it.

A good partner to bond with is hydrogen.

So it has four valence electrons and then hydrogen

has one valence electron, so they can each share an

electron with each other and then they

both look pretty happy.

I said eight's the magic number for everybody except

for hydrogen and helium.

Both of them are happy because they're only trying to fill

their 1s orbital, so the magic number for

those two guys is two.

So all of the hydrogens now feel like

they have two electrons.

The carbon feels like it has eight.

Now, there's several ways to write this.

You could write it just like this and you can see the

electrons explicitly, or you can draw little lines here.

So I could also write this exact molecule, which is

methane, and we'll talk a little bit more about why it's

called methane later in this video.

I can write this exact structure like this: a carbon

bonded to four hydrogens.

And the way that I've written these bonds right here you

could imagine that each of these bonds consists of two

electrons, one from the carbon and one from the hydrogen.

Now let's explore slightly larger chains.

So let's say I have a two-carbon chain.

Well, let me do a three-carbon chain so it really

looks like a chain.

So if I were to draw everything explicitly it might

look like this.

So I have a carbon.

It has one, two, three, four electrons.

Maybe I have another carbon here that has-- let me do the

carbons in slightly different shades of yellow.

I have another carbon here that has one,

two, three, four electrons.

And then let me do the other carbon in that first yellow.

And then I have another carbon so we're going to have a

three-carbon chain.

It has one, two, three, four valence electrons.

Now, these other guys are unpaired, and if you don't

specify it, it's normally going to be hydrogen, so let

me draw some hydrogens over here.

So you're going to have a hydrogen there, a hydrogen

over there, a hydrogen over here, a hydrogen over here, a

hydrogen over there, a hydrogen over here, almost

done, a hydrogen there, and then a hydrogen there.

Now notice, in this molecular structure that I've drawn, I

have three carbons.

They were each able to form four bonds.

This guy has bonds with three hydrogens and another carbon.

This guy has a bond with two hydrogens and two carbons.

This guy has a bond with three hydrogens and then this carbon

right here.

And so this is a completely valid molecular structure, but

it was kind of a pain to draw all of these

valence electrons here.

So what we typically would want to do is, at least in

this structure, and we're going to see later in this

video there's even simpler ways to write it, so if we

want at least do it with these lines, we can

draw it like this.

So you have a carbon, carbon, carbon, and then they are

bonded to the hydrogens.

So you'll almost never see it written like this because this

is just kind of crazy.

Hyrdrogen, hydrogen-- at least crazy to write.

It takes forever.

And it might be messy, like it might not be clear where these

electrons belong.

I didn't write it as clearly as I could.

So they have two electrons there.

They share with these two guys.

Hopefully, that was reasonably clear.

But if we were to draw it with the lines, it

looks just like that.

So it's a little bit neater, faster to draw, same exact

idea here and here.

And in general, and we'll go in more detail on it, this

three-carbon chain, where everything is a single bond,

is propane.

Let me write these words down because it's helpful to get.

This is methane.

And you're going to see the rhyme-- you're going to see

the reason to this naming soon enough.

This is methane; this is propane.

And there's an even simpler way to write propane.

You could write it like this.

Instead of explicitly drawing these bonds, you could say

that this part right here, you could write that that part

right there, that is CH3, so you have a CH3, connected to

a-- this is a CH2, that is CH2 which is then connected to

another CH3.

And the important thing is, no matter what the notation, as

long as you can figure out the exact molecular structure, as

long as you can-- so there's this last CH3.

Whether you have this, this, or this, you know what the

molecular structure is.

You could draw any one of these given any of the others.

Now, there's an even simpler way to write this.

You could write it just like this.

Let me do it in a different color.

You literally could write it so we have three carbons.

So one, two, three.

Now, this seems ridiculously simple and you're like, how

can this thing right here give you the same information as

all of these more complicated ways to draw it?

Well, in chemistry, and in organic chemistry in

particular, any of these-- let me call it a line diagram or a

line angle diagram.

It's the simplest way and it's actually probably the most

useful way to show chains of carbons or to

show organic molecules.

Once they start to get really, really complicated, because

then it's a pain to draw all of the H's, but when you see

something like this, you assume that the end points of

any lines have a carbon on it.

So if you see something like that, you assume that there's

a carbon at that end point, a carbon at that end point, and

a carbon at that end point.

And then you know that carbon makes four bonds.

There are no charges here.

All the carbons are going to make four bonds, and each of

the carbons here, this carbon has two bonds, so the other

two bonds are implicitly going to be with hydrogens.

If they don't draw them, you assume that they're going to

be with hydrogens.

This guy has one bond, so the other three

must be with hydrogen.

This guy has one bond, so the other three must be hydrogens.

So just drawing that little line angle thing right there,

I actually did convey the exact same information as this

depiction, this depiction, or this depiction.

So you're going to see a lot of this.

This really simplifies things.

And sometimes you see things that are in between.

You might see someone draw it like this, where they'll write

CH3, and then they'll draw it like that.

So that's kind of combining this way of writing the

molecule where you write the CH3's for the end points, but

then you implicitly have the CH2 on the inside.

You assume that this end point right here is a C and it's

bonded to two hydrogens.

So these are all completely valid ways of drawing the

molecular structures of these carbon chains or of these

organic compounds.