Organic Chemistry Naming Examples 3

Organic Chemistry Naming Examples 3

We've got a few more molecular
structures to name, so let's

look at this first
one right here.

The first thing you always want
to do is identify the

longest chain.

If we start over here, we have
one, two, three, four, five,

six, seven, eight, nine, ten,
eleven, twelve, thirteen

carbons, looks pretty long.

Now what if we start
over here?

This looks like it could also
be a long chain: one, two,

three, four, five, six, seven,
eight, nine, ten, eleven,

twelve, thirteen.

So we have two different chains,
depending on whether

we want to go up here or whether
we go over here, that

have a length of thirteen.

So you're probably asking, which
chain do you choose?

You should always, if we have
two chains of equal lengths

and they're the longest chains,
you pick the one that

will have more branches or
more alkyl groups on it.

So this group right here, if we
pick this from here to here

as our chain, we only have
one group on it,

that group up there.

If we pick this chain, starting
over here and then

going over here, we have
two groups on it.

We would have this group over
here and then we would have

this group over here.

This is the better chain
to use because it has

more groups on it.

It has more groups,
but the groups

are smaller and simpler.

So let's start counting.

And the direction we want to
count, we always want to start

on the side of the chain where
we're going to encounter

something first, and everything
is closer this end

of the chain so we'll
start counting here.

One, two, three, four, five,
six, seven, eight, nine, ten,

eleven, twelve, thirteen, so
we have thirteen carbons on

our main chain.

Let me draw our main chain.

So our main chain is this thing
in orange I'm drawing

right here.

That is our main chain.

Thirteen, that's
three and ten.

The prefix is tridec- and it's
tridecane because we have all

single bonds here, so
it's tridecane.

Tridecane is the main chain.

Then we have two groups
over here.

This one in green, this only has
one the carbon branching

off of the main chain, so it's
prefix will be meth- and it'll

be a methyl group, so
that is methyl.

That is a methyl group
right there.

Then this one down here, we have
one, two, three carbons.

the prefix is prop-, so this
is a propyl group.

And the methyl is sitting on the
three carbon of our main

chain and the propyl group is
sitting on the four carbon:

one, two, three, four.

Now when we figure out what
order to list them in when we

actually write out the name,
M, we just do it in

alphabetical order.

M comes before P, so we write 3-methyl before 4-propyl.

The entire compound here is
or the entire molecule is

3-methyl-4-propyltridecane And
this is actually all going to

be one word.

You use dashes to separate when
you have numbers, but if

you have a word followed by
a word, it just becomes

propyltridecane, so
3-methyl-4-propyltridecane.

And we're done.

Let's do this one down here.

Now this one seems a little
bit more complex.

The first thing to see is what
is the largest chain or

the largest ring that we have
in our structure?

The two candidates, we have
this chain over here.

This has one, two, three, four,

five, six, seven carbons.

Let's see how many carbons
our ring has.

Our ring has one, two, three,
four, five, six, seven, eight,

nine carbons.

So the ring is the largest
core structure in this

molecule, so that will be
our core structure.

We have nine carbons-- let me
highlight it-- so the ring is

this right here.

It has nine carbons.

The prefix for nine is non-.

It's all single bonds, so it's
nonane, and it is in a cycle.

It's a ring, so it's
cyclononane.

This part right here, that
part right there, is

cyclononane.

We have several things that
branch off of the cyclononane,

so let's look at them one at a
time, and then we'll think

about how we're going to number
them on the ring.

We looked already at this at
this chain that has seven

carbons: one, two, three,
four, five, six, seven.

So that is a heptyl group.

This over here, let's see
what we're dealing with.

We have one, two, three carbons,
so that is just a

standard propyl group.

Then here, we have one, two,
three, four carbons, so we

could say this is
a butyl group.

But this isn't just
any butyl group.

If we use the common naming,
the carbon we immediately

touch on or that we immediately
get to when we go

off of our main ring, that
branches off into three other

carbons, so this is tert-,
tert- for three.

The tert- is usually
written in italics.

It's hard to differentiate
that when you see it.

I'll write it in cursive.

This is tert.

This is a tertbutyl group.

Now, the next question is how
do we specify where these

different groups sit
on this main ring?

If you just had one group, you
wouldn't have to specify it,

but when you have more than one,
what you actually do is

you figure out which one would
be alphabetically first, and

that would be number one.

Now, we have an H in heptyl, a
P in propyl, and tert-butyl,

you might say, well, do I use
the T or do I use the B?

And this is just the convention,
you use the B.

If you have sec-butyl or
tert-butyl, you ignore the

sec- or the tert-.

If this was an isobutyl or an
isopropyl, you actually would

use the I, so it's a little
bit-- I guess the best way to

think about it is there's a dash
here so you can kind of

ignore it, but if this was
isobutyl it would all be one

word, so you would
consider the I.

So in this situation, we would
consider the B, and B comes

before P or an H, so that
is where we will

start numbering one.

Then to figure out which
direction to keep numbering

in, we just go in the direction
where we're likely

to encounter the first or where
we will encounter the

first side chain, so we'll go
in this direction because we

get right to the propyl group.

One, two, three, four, five,
six, seven, eight, nine.

So this compound, we're going
to start with the

alphabetically first side chain,
so it's 1-tert-butyl.

I'll write this in cursive.

1-tert-butyl.

Then the next one
alphabetically

is the heptyl group.

That's H for heptyl, so
then it is 5-heptyl.

And then we have the propyl, and
then it is 2-propyl, and

then finally cyclononane,
and we're done!