Hi! Welcome to ChemSimplified. I'm Dr. K and in this video,
we are going to go through how to draw structural formula for organic compounds using three examples.
Chances are high that when you encounter the structures for organic
compounds, they don't always come in the same form, so, it'll come in handy if you
know how to draw structures using different ways, like expanded, condensed
and bond-line or skeletal forms. Before we dive in, let's take a look at how each
of the three structural formulas look like. Here's how an expanded structural
formula looks like. Notice all the bonds connecting the atoms are shown in the
expanded form? This is the closest form drawn from Lewis structure.
Next is condensed structural formula. In condensed structural formula all of the
bonds connecting carbons to hydrogens are not shown. Instead they are condensed
into groups of CH3, CH2 and CH. Lastly is the bond line or the skeletal structural formula.
In this form, it's basically what the name says skeletal. It doesn't show
out the atoms for carbons and hydrogens. It only shows the bond
connecting them and if there are other atoms in the molecule like bromine in
our example, then it will be written out. So now that we are familiar with how
these three types look like, let's go ahead and try with our first example,
drawing from expanded and we move to condense and then from condense we draw
to bond line. So let's start with our first example. It's an alkyl halide. Don't worry
about it if you're not able to classify the compound at this point. I'll put a
link to the introduction to the organic compound on the top right of this video.
So before we begin drawing from expanded to condensed, it would be a good idea to
start numbering our compound, our parent chain which is basically the longest
chain that you can count from one end to the other continuously and whatever that
is not on the chain that's attached to the chain those are the substituent.
So let me demonstrate. So if we look at our expanded structure
right now I can label from one end to the other like this and whatever that's
not on the carbon like for example bromine and CH3, these
would be our substituents. So right now in our structure we have bromine
attached to carbon 1, CH3 attached to carbon 4. Don't worry about it too
much in terms of numbering unless you need to know how to name the
nomenclature and in that case I will post related videos in the description
box below. So based on our expanded structure we have five carbon and
bromine on carbon 1 and CH3 group on carbon 4. So in the condensed
structure what we're gonna do is basically just condense out all the CH
groups so it will look like this. So notice Br is still connected to
carbon 1 and CH3 is connected to carbon 4 and the rest of it we just
don't show out the vertical bonds like the carbon and the hydrogen bonds.
Instead we only show the carbon and carbon bonds and sometimes you'll notice
that the bonds between the carbon and carbon are not shown and that is fine as
well. So it may look something like this and this is still fine because bromine
is too attached to the first carbon and CH3 is still attached to the carbon 4
and sometimes you may also find that when is condensed further the CH3 or
carbon 4 is not drawn out it will just be written as part of the formula.
And it will look like this so bromine on carbon 1, that's fine.
The CH3 is written squashed between carbon 3 and carbon 4 and that is
fine as well. So condensed form, there are several ways of drawing it out depending
on your preference and if you want to show the bonds between the carbon that
would be the first example if you want to take out the bonds between the carbon
that would be the second example if you want to take out the all the bonds
between the carbons and not showing how the
substituent is connected you can embed it in between the atoms and show in a
third example. If that's a little bit too difficult for you then stick with the
first or the second way of drawing condensed form. Now we move on to
bond-line or a skeletal structure so we have 5 carbon we'll number it
1, 2, 3, 4, 5 and bromine on the first carbon, CH3 on the fourth carbon and
that's how it looks like very clean very simple very straightforward. So every
point in our skeletal structure represents a carbon and the
corresponding number of hydrogens. So we know that carbon forms four bonds so for
example if we look at our first carbon in the skeletal structure there are 2 bonds.
1 to bromine and 1 to carbon number 2, so from that structure we
know that carbon 1 should have two hydrogens and if we refer to the
expanded or the condensed form we can see that carbon number 1 has two hydrogens.
And now we move on to like for example carbon 5. So if you look
at carbon 5, carbon 5 in the skeletal structure only has one bond so
that means carbons supposed to have 4 bonds, so 4 minus 1 will give us 3.
So carbon 5 will have 3 hydrogens attached to it, so it's a CH3.
Make sense? So this is how the structures look like without all the circling and
the numbering. So expanded form moving into condensed it's cleaned up a little
bit we don't show that many bonds we group our CH groups and condensed move into
bond line or skeletal we clean it up even further so we don't even write out
carbons and hydrogens and we only show the bonds between carbons to carbon.
No bonds carbon to hydrogens are shown. Ok? Feeling good? Let's try our second example.
So this is our expanded structure.
This is an alkene. So in our structure we have 1, 2, 3, 4, 5. 5 carbons again. There are
something a little bit different here. There's a double bond
between carbon 2 and carbon 3 and also there's that same CH3 group on carbon 4.
Now we're gonna move on to a condensed structure. So like we've already went
through with the first example, condensed structure means we will just not show
the carbon hydrogen bond instead we are just going to group it up together.
So let's start off by drawing out the C-C double bond between carbon 2 and carbon 3.
If you notice because of the double bond carbon 2 only has two other bonds
attached to it. Same goes to carbon 3 so that's why I have these two bonds
sticking up and down on carbon 2 and carbon 3. Now let's fill out the bonds so
carbon 2 there are two groups to attach to it one is carbon 1 which has 3
hydrogens so I group it up as CH3. That's carbon 1. The other group attached to
carbon 2 aside from CH3 is a hydrogen. Okay, now let's look at carbon 3.
Carbon 3, there are two groups attached to it,
one is a hydrogen and the other one is carbon 4 and since carbon 4 has
hydrogen and then a CH3 and another CH3 group attached to it, I just went ahead
and condensed up the CH so I wrote it as a CH for carbon 4 and then carbon 4
is connected to basically two CH3 groups. So the first CH3 group is our carbon 5
and the other CH3 group is our substituent. Okay, alright! So now we move
to skeletal structure. So skeletal structure, the first thing we do is we
draw out the skeleton so we have a skeleton of five carbon which means we
will do a zigzag containing five points. So if you notice I have five points here
1, 2, 3, 4, 5 and between our carbon 2 & 3 there should be another line, two lines
total to represent a double bond because right now everything is single bonded so
I'm gonna put in a double bond between carbon 2 and carbon 3 so there we go so
now we have a double bond between C2 and C3 and now we need to stick in our
CH3 group and that's at carbon 4 that's our CH3 at carbon number 4.
Okay, moving on to our third example. This is a carboxylic acid. So we only have
four carbons in this example. C double bond O is on the first carbon, OH is
also on the first carbon. So COOH, C double bond O, OH can be shortened or
condensed to look like this COOH and then we're gonna put in our
second carbon which is CH2 ,third carbon which is also CH2 and the fourth carbon
which is CH3 and that's it. Pretty easy, right? Okay, moving on to bond line or
skeletal so this is pretty easy as well. Same like what we did for the second
example we count how many carbons we have in our skeleton and in this case we
have four carbons so I'm gonna draw a zigzag containing four points like this
1, 2, 3, 4. Ok now on the first carbon I am going to attach my C double bond O and
then I'm going to attach my OH. And that's it. So we're all done. We went
through three different types of structural formula - expanded, condensed
and skeletal. So which structural formula do you like the most? Do comment below as I
would love to hear from you. Do subscribe if you find this video helpful and click
on the bell icon so you can notify on new videos for more info please head
over to ChemSimplified.com, you will find a blog post related to this video.
Thank you for watching and I'll see you in the next video.
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