Lecturer: The next few videos
we're going to look at the nomenclature and properties of
carboxylic acid derivatives. Let's start with an acyl halide. Here's our general
structure of an acyl halide. On the left side we have an acyl group, on the right side we have a halogen. You could also call this acid halides. They're derived from carboxylic acids. If we look at this carboxylic
acid on the left here, a two carbon carboxylic acid, we could convert that to a two carbon acyl halide over here on the right. If we want to name our acyl halide we have to think about the name
of the carboxylic acid. This, of course, is acetic acid. Let's go ahead and write
out acetic acid here. If we want to name the
corresponding acyl halide we need to think about dropping the
-ic ending, and then the acid. We drop -ic and acid, and we
add -yl and then the halide. Let's go ahead and write that out, so we drop the -ic and we add the
yl and then we add the halide. We have a chlorine here so
we're going to write chloride. We would call this acetyl chloride. Let's go ahead and show that right here. We add the -yl and then
we add the halide portion. We could have also called
this ethanoic acid. Ethanoic acid would be the IUPAC name but everyone says acetic acid. If we were to call this ethanoic acid, once again think about drop
your -ic and then the acid part, drop this portion, then
add -yl and then chloride. Let's go ahead and write that in here. We go ahead and add the -yl in
and then the chloride like that. That would be ethanoyl
chloride as our name. Let's go ahead and show this portion, once again, the -yl portion
and then our halide. In terms of physical properties
of acyl halides we need to think about the interaction
of two molecules here. Let me go ahead and draw in another molecule of acetyl chloride. Acetyl chloride has a boiling point of approximately 51 degrees Celsius. Let me go ahead and write that in, so approximately 51 degrees Celsius. We know that acetyl chloride
is a polar molecule. The oxygen here is more
electronegative than this carbon, so we have a partial negative
and we have a partial positive. This chlorine is also
withdrawing electron density from our partially positive carbon,
so we have a polar molecule. Acetyl chloride is polar right here. This is polar. Same molecule so this is polar. We have a partial
negative, partial positive. Once again this chloride is also withdrawing electron density this way. We have two polar
molecules interacting which we know is a dipole dipole
intermolecular force. There's an attractive force between these molecules which is dipole dipole. Let me go ahead and write that. It's a dipole dipole interaction
with molecules of actyl chloride. We know that dipole dipole
interactions are stronger than London dispersion forces, so
acetyl chloride has a higher boiling point than say a two
carbon alkane, like ethane. It's a little bit harder
to pull these molecules apart than it is to pull
molecules of ethane apart, therefore this boiling point is higher than that for a two carbon alkane. However this boiling point is
lower than that of acetic acid. To think about that we'll need to draw in another molecule of acetic acid. Let me go ahead and do that. Drawing in another
molecule of acetic acid. We can see that there's
opportunities for hydrogen bonding. There's a hydrogen bond here,
and a hydrogen bond here. Hydrogen bonding, go ahead and write that. Hydrogen bonding is the strongest
type of intermolecular force. Therefore the boiling point
of acetic acid is going to be higher, it's somewhere
around 118 degrees Celsius. It's harder to pull these two molecules apart because hydrogen
bonding is a stronger intermolecular force than dipole dipole. That gives you some idea of the
boiling point of acyl halides. In terms of solubility
in water you can't really say that something like
acetyl chloride is soluble in water because it reacts
so violently with it. Acetyl chloride is extremely
reactive and it reacts very quickly and often
violently with water, so we can't really say
that it dissolves in water. Let's move on to acid anhydrides. Let's look at how to
name an acid anhydride. Acid anhydrides can be thought of as being derived from carboxylic acids too. If we look over here in
the left once again we have acetic acid here,
this is acetic acid. If we take two molecules
of acetic acid and combine them we can
form an acid anhydride. Let's think about what happens. We're going to lose water here and the word anhydride means without water. If we take off the water
and take this portion, take this acyl group and
this over here and stick them together, then we form our
anhydride over here on the right. Because our anhydride was formed from acetic acid we call this acetic anhydride. These are pretty simple names. You keep the acetic part and drop the acid, and just add anhydride. This is acetic anhydride. If you thought of acetic
acid as ethanoic acid, if you prefer to use the
IUPAC name, ethanoic acid. Let me write ethanoic acid here. Once again just drop the
acid part and add anhydride. You could call this ethanoic anhydride. Ethanoic anhydride. Once again anhydride
meaning without water. Let's look at how to
name another anhydride. Let me go down here
and get some more room. We're trying to name this
anhydride over here on the right. To do that we need to think
about the carboxylic acid, from which it can be
thought of as being derived. Here we have two
molecules of benzoic acid. Let's go ahead and
write benzoic acid here. I'm not talking about
exact chemical reactions, I'm just thinking about
the acid anhydride and how to put it into the
different carboxylic acids. If we do the same thing we did before, we think about the term
anhydride being loss of water, we take out water here
and stick those together, once again you can see we form
the anhydride on the right. This portion plus this portion
gives us our acid anhydride. Once again we're not doing
exact chemical reactions here. Just for the sake of nomenclature we can just drop the acid and add anhydride. This would be benzoic anhydride. This would be benzoic
anhydride, like that. Let's look at another example. This time we don't have symmetry. When I'm thinking about some
carboxylic acids for this one, over here on the left I
recognize benzoic acid. Let me go ahead and write that down. Benzoic acid is being present. If I think about over on the
right side, this portion, if I think about a carboxylic acid this way I see that's acetic acid. I have benzoic acid and acetic acid. To name our anhydride we drop the acid part and we're
going to add anhydride. We have to think about
using the alphabet here. A comes before B, so to
write the name of our anhydride we would write
acetic benzoic anhydride. Acetic benzoic anhydride. Once again when you see
an anhydride and you're trying to name it just think
about the carboxylic acids and that will help you
figure out the name. In terms of physical properties of acid anhydrides let's
look at an example here. Over here on the left we have acetic anhydride, which
is a polar molecule. It's moderately polar because
we have these carbonyls here. The oxygen is partially negative, this carbon down here
is partially positive, the same thing for all these carbonyls. It's a moderately polar molecule. That's a negative sign right there. There's going to be some
attraction between these molecules. There's going to be
some attraction between the negative and the positive charges. We have a fairly polar
molecule and a fairly polar molecule, so we can say that there's some dipole dipole interaction present. Between molecules of acetic anhydride there's some dipole dipole interaction. There's also of course London
dispersion forces as well. The boiling point for
acetic anhydride turns out to be approximately
140 degrees Celsius. Let's go ahead and write that in here, so approximately 140 degrees Celsius. We can compare that to
a carboxylic acid that's similar in terms of number
of carbons and oxygens. For acetic anhydride we had
one, two, three, four carbons. Over here on the right
this is butanoic acid. We have one, two, three, four carbons. Then we have two oxygens
for butanoic acid and we have three oxygens
for acetic anhydride. They're similar in terms of sizes, but when we think about
comparing their boiling points, over here on the right
butanoic acid has a boiling point of approximately
164 degrees Celsius, it has a higher boiling point because once again there's some
hydrogen bonding present. There's some hydrogen
bonding present because we're talking about a
carboxylic acid here. And once again hydrogen bonding
is a stronger intermolecular force than dipole dipole so
it's harder to pull apart molecules of butanoic acid,
therefore it takes more energy, it takes a higher
temperature to pull these molecules apart to turn them into a gas. Once again, H-bonding is a stronger intermolecular force than dipole dipole. When we think about the solubility of an acid anhydride in water, once
again it's kind of difficult. Something like acetic anhydride is going to react with the water. Acetic anhydride is also fairly reactive. Not quite as reactive as an acyl halide but it does react with water, so we can't really say that it
dissolves very well in it. We'll talk much more
about the reactivity of these carboxylic acid
derivatives in a later video.