Leah here from leah4sci.com and in this video
we'll take a look at common functional groups
that you have to know in your Organic Chemistry
course. Be sure to check out my functional
group quiz and cheat sheet as well as the
videos on how to name each particular group
by visiting my website leah4sci.com/Naming.
So what is a Functional Group? In Organic
Chemistry you'll see a lot of molecules that
are made up of carbons and hydrogens. You
can get many complex structures and many isomers
from just carbons and hydrogens. Before molecule
to be reactive it tends to have other atoms
with different electronegativities, different
electrons, concentrations, pi bonds. Those
specific groups, those are your functional
groups.
Now before we go into Functional Groups, I
want to talk about one type of group that
you'll see that's not functional group at
all and that's the R group. As we look into
your textbook you'll see molecules that has
carbons, oxygens, nitrogens, and an R group.
But an R group does not represent a specific
collection of atoms, instead the R group tells
you what you have on the rest of the molecule.
For example, if I'm looking at this structure
here, but then I have a complex group of a
C double bound O, single bound O, single bound
to another C with three hydrogens and I specifically
want to focus on this portion of the molecule.
I don't want to look at the carbon chain,
it's not my priority for this discussion.
So instead of reading this entire molecule
and the group that I boxed off, I'll turn
the entire purple portion in R for the rest
of the molecule, and then simply focus on
the ester here which is a CO2CH3. R is the
rest of the molecule that I don't want to
focus on right now but I still acknowledge
that it's there. When talking about functional
groups, you'll typically see R-functional
group to show that it can come up at any type
of molecule.
Another thing to discuss before we go into
Functional Groups are the type of carbon chains
that you're going to see specifically the
Alkane, Alkene, and Alkyne. Notice the ending
Alkane is "ane", Alkene is "ene",Alkyne is
"yne". And this tells you the number of pi
bonds specifically carbon to carbon pi bonds
that you're going to see. An Alkane has no
pi bonds between carbon atoms, that means
every atom is single bound to another carbon.
You'll see this drawn out in line structure
as a zigzag where every carbon is sp3 hybridized
with an ideal bond angle of 109.5 degrees.
An Alkene is a molecule that has at least
one double bond between carbon atoms.You'll
see that as carbon double bound to carbon
where the first bond is the sigma and that's
with your hybridized orbitals and the second
is a pi bond sitting in the p-orbitals. In
line structure, it'll look the same as your
alkane except that you'll see a second line
representing the pi bond. You can have more
than one double bond on a molecule as long
as they're different carbon atoms that have
the pi bond so that each is still considered
a double bond. The carbons holding the double
bond are sp2 hybridized with a bond angle
of 120 degrees.
And finally we have the Alkyne which is a
triple bond between two carbon atoms. Notice
here we have two double bond because each
individually has a double bond, but with an
Alkyne you'll see a three lines between two
carbon atoms. The first is at sigma and that's
on your sp hybridized carbon, the second and
third are your pi bonds sitting in p-orbitals,
one in the p y and one in the p z. Many professors
will try to represent a triple bond the same
way as a double and a single in terms of a
zigzag, but this is incorrect and I don't
like it. And that's because a triple bond
is sp hybridized with a bond angle of 180
degrees and so the correct way to represent
it is something like this. You wanna have
a linear line where the triple bonds sits
between the two carbon atoms, that would be
this two right here, but the two carbon atoms
or other atoms on either direction of the
triple bond are also in a straight line because
of that 180-degree bond angle. Now that you
understand it, let's memorize it. I have to
memorize as 1, 2, 3, ane, ene, yne. Ane is
one, single bond, ene is two, double bond,
yne is three, triple bond.
The first and simplest functional group we'll
look at is the Alkyl Halide or the Haloalkene.
Recall from general chemistry that group 7
on the periodic table are your halogens or
your halides, that's where we get the alkyl
halide and these are Fluorine, Chlorine, Bromine,
and Iodine, in that order going down the group.
If you have a carbon chain with any halogen
attached to, that is considered an Alkyl Halide
or a haloalkane and you just insert the name
of the halogen to be more specific. So for
example, if I put a Chlorine on the primary
carbon here, I will get a primary Alkyl Chloride
or Chloroalkane or simply a primary alkyl
halide. If I place Iodine on the secondary
carbon, I get a secondary Alkyl Halide. If
you're comfortable identifying your Primary,
Secondary, and Tertiary carbons, make sure
you study my Pencil Trick Tutorial linked
on the description below. And if I place a
Fluorine on a tertiary carbon I get a tertiary
halogen or a tertiary alkyl halide. These
are very important to understand and recognize
because they will play a big role in the reactions
moving forward especially substitution and
elimination reactions.
The next functional groups I want to look
up are the Amines which have n in the word
where n stands for the Nitrogen atom. An Amine
is a molecule that has Nitrogen bound to Carbon
and this could be bound to a 1, 2 ,3 or 4
carbons to give you a different type of Amine.
To show you the different types of Amines,
we'll use R to represent the rest of the molecule.
If I have R bound to an NH2, remember a Nitrogen
can have three bonds. This is considered a
primary amine because it's bound to one R-group.
If I have R bound to Nitrogen which is bound
to a second R, which we'll show as R-prime,
this is considered a secondary amine because
Nitrogen is bound to two R-groups. If I have
a Nitrogen bound to three R-groups, that's
R, R-prime, and R double prime. That's a tertiary
amine and these are the common ones we're
going to see. But every now and then you'll
see a Nitrogen bound to four R-groups that'll
be bound to R, R prime, R double prime, and
R triple prime. If you'll do a quick formal
charge, you will recognize that the Quaternary
Amine has a positive charge because Nitrogen
prefers to have three bonds and one lone pair.
But if and when it comes out recognize that
yes a Quaternary Amine does exist. And the
key to recognizing the Amine functional group,
Amine spelled with an n has the key atom Nitrogen.
Many of the remaining functional groups will
have Oxygen in them and the key is to recognize
the difference between how the Oxygen is attached
to the parent chain. The alcohol has COH in
a name where C can be a part of your R-group.
So if you have your R-group and attached to
that you have a C, an O, and an H, that's
an Alcohol where the alcohol is the OH or
Hydroxyl group. Hydroxy comes from the word
Hydrogen and Oxygen. So if you see a carbon
chain with an OH on the primary carbon, that's
a primary alcohol. If the OH was on the tertiary
carbon, that would be a tertiary alcohol.
A similar functional group is the Thiol which
you'll notice sounds like Alcohol, it ends
in OL which is how you identify an alcohol,
but the Thi portion of the molecule represents
the sulfur atom. So if we take a molecule
and draw an alcohol, but now we erase the
Oxygen and replace it with a sulfur, this
is a sulfur alcohol or simply a Thiol. Recall
that sulfur sits on the Oxygen on the periodic
table so they have very similar binding ability.
The next group I want to look at is the Ether
and this is one of the first confusing functional
group. An ether is represented by R,O,R. We
have an Oxygen sitting between two carbon
groups. You can have a symmetrical ether,
for example if I have CH3-O-CH3, this is dimethyl
ether because I have two methyls surrounding
that Oxygen. You can also have an asymmetrical
ether, for example, if I have a CH3 bound
to an O, the second R-group is a CH2CH3 or
an ethyl group, this is ethyl methyl ether
where the tro R-groups are different. And
in this case we have to write it as R-O-R
prime. A good trick to remember the Ether
is to think of the word Either, it looks like
we have R-O-R, we have either R or something
else. Ether or Ether has OR in the word. Do
not confuse the Ether with an Ester which
we'll look at shortly. Ethers can exist as
a linear chain like we see here, or you can
see a cyclic ether. For example if I'll show
you a five numbered ring where we have four
carbon atoms and one Oxygen, this is still
an ether, it's a cyclic ether, it's one that
you'll have to know later in your Organic
Chemistry reactions. This is tetrahydrofuran
or THF, which comes up a lot on reactions.
You don't have to memorize the name of cyclic
ether except for this one, the Epoxide. Epoxides
are very reactive and will come up a lot in
Organic Chemistry so I want you to recognize
it. Epoxide is a three membered ether, we
have a three atom ring, two carbons and one
Oxygen. You can have carbons or Hydrogen coming
off of it but the key is the small triangle
made up of two carbons and one Oxygen giving
you an epoxide. The next set of functional
groups we'll look at will have the carbonyl
in common. Where carbonyl is C double bound
O. This will be very important later on because
the carbonyl has resonance and that means
you get a partial positive on a carbon and
a partial negative on Oxygen. But for now
we'll focus just on the structure. And since
there's a pi bond between them, where the
carbon and Oxygen are sp2 hybridized with
a bond angle of 120 degrees.
When you have the carbonyl in the middle of
the chain, meaning the carbonyl has R-groups
on either side, you get a ketone. The way
I remember this is Ketone ends in "one". A
ketone does not want to be alone, one it doesn't
wanna be alone, and therefore it's surrounded
by R-groups on either side. If I wrote this
out showing the atoms we would see CH3 bound
to the carbonyl, bound to the CH3 because
it's in the middle, it doesn't want to be
alone. Just like the Ether, the Ketone can
be symmetrical, in this case we have two methyl
groups, or it can be asymmetrical if I replace
the methyl group on the right with an ethyl
group. This is also a ketone. If you see this
written out, you'll see this as R carbonyl
and R or R prime depending on if the second
R-group is the same or different. Or of the
pi bond are not being shown, this is R C O
R. Don't mix this up with an Ether which was
just R-O-R because we have the carbon there,
it's not an Oxygen in the chain, instead it's
a carbon in the chain double bound to an Oxygen
atom.
Aldehydes are very similar to ketones so don't
confused the two. The aldehyde also has a
functional group on a carbon chain but in
the aldehyde's case it's not in the middle
of the molecule like the ketone that doesn't
want to be alone. Instead, the carbonyl is
at the end of the molecule so that the last
atom here is the Hydrogen. The aldehyde has
an H in the word to remind you that there
is a Hydrogen in the end rather than another
carbon or another R-group. If we write this
our we have CH3CH3CH2 for the propyl group,
then we'll have C double bound O for the carbonyl
and H for the Aldehyde. If you want to write
this out in simple terms,it'll be R carbonyl
H instead of R carbonyl, R prime like the
ketone or we can write it out even simpler,
RCHO. This is another source of confusion
for students, I wanna make sure you understand.
RCHO has the carbon then the hydrogen then
the Oxygen telling you that it's carbon, then
bound to Hydrogen, the Hydrogen sits on the
carbon and the Oxygen has to come back and
be written on the carbon. Don't confuse this
with the alcohol which we showed as RCOH,
if it's O then H it's an alcohol because you
have carbon followed by Hydroxyl OH. But an
aldehyde is not Hydroxy, it's HO giving you
a completely different functional group and
a completely different molecule.
The next functional group I want to look at
is a carboxylic acid and this is another source
of confusion for students so make sure you
understand. The carboxylic acid has a carbon
chain with a carbonyl at the end. C double
bound to O and then attached to that, we have
an OH. Students will look at this and think
"oh! I have a carbonyl and then alcohol",
but that is not the case. Whenever you see
a carbonyl directly attached to an OH, that
is not an alcohol attached to an aldehyde,
that is a brand new functional group, the
carboxylic acid. If we'll write this out we
have CH3CH2 for the upper portion, then the
carbonyl and OH. If we want to write this
out even more simply, we can have R to represent
the ethyl group or the rest of the molecule
, COOH. You'll also see it as RCO2H. We're
showing that there are two Oxygens on this
functional group. One Oxygen sitting on the
carbon in a double bond, the second Oxygen
sitting on the side as an OH. As you'll see
late in Organic Chemistry 2, carboxylic acids
can be reactive so that the OH is swapped
for another group and those are your Carboxylic
Acid derivatives giving you a whole new set
of functional groups.
The first one we'll look at is what happens
when we take that OH on the carboxylic acid
and replace it with an OR. This molecule is
called an Ester. For example, if we swap this
R-group for a CH3, we'll have CH3, CH2, C
double bound O, single bound O, single bound
CH3, for a methyl ester, because it's a methyl
sitting on the longer parent chain. If you
wanna write this out the short way, the ester
is RCO2R prime. Just like a carboxylic acid
RCO2 or RCOO, but instead of a Hydrogen at
the end, we have an R-group at the end. Esters
are often confused with Ethers so I want to
make sure you'd see them together and understand
the difference. If we have an Ester that's
R CO2 R-prime, and Ether is just R-O-R prime.
Remember for Ethers we said it's either OR,
that's it. It's R and O R, nothing else. Either
R or the OR. An Ester has an S. Think of that
S as standing for your second R-group. Because
Ester looks like a Carboxylic acid but it
has a second R-group and then the example
we saw above that's second R-group as a methyl.
One more time we have our carboxylic acid
but this time, I'm going to replace that OH
with the Nitrogen. So for example if I replace
it with an NH2 I get a new functional group
and this one is the Amide. Amide sounds very
much Amine, but remember the Amine, we set
"n" for Nitrogen. When Nitrogen was the primary
focus on the functional group because we have
just Nitrogen and carbon, R-groups, nothing
else. The Amide looks like a carboxylic acid
and sounds like Amine. We'll it looks like
a carboxylic acid because it's a carboxylic
acid derivative and it sounds like Amine because
we have a Nitrogen in there and the 'd" is
to remind you that in addition to the Amine
portion, we also have a double bond carbon
Oxygen. "D" for double bond carbon to Oxygen
on a molecule that sounds like Amine. Just
like Amines, when it comes to amides, it doesn't
have to be just an NH2. We can have NH2, a
simple Amide, or we can add some R-groups
in there.
For example I can put a CH3 with one Hydrogen
or 2 CH3s or any R-group. I just chose methyl
with no Hydrogen, because Nitrogen remember
likes 3 bonds and 1 lone pair. These are different
types of molecules that you have to recognize
as an Amine. It sounds like an Amine, it looks
like an Amine, but the D reminds you that
there's also a double bond carbon to Oxygen
in that same functional group. There's another
Nitrogen containing another functional group
that has R and then C triple bound N. This
right here is called a Nitrile, it's also
referred to as a cyano group because CN- is
cyanide comes from cyanic acid. This will
come up in your Organic Chemistry reactions
so make sure you do recognize it, the Nitrile
has a C triple bound to N on the carbon chain.
The last group we'll look at is not really
a functional group but it comes up so often
and students mixed it up so often so I wanna
make sure you're clear on the difference.
Phenol vs. Phenyl. A Phenyl and a Phenol,
they kinda sound similar but a Phenol ends
in OL which tells you that it's an alcohol,
right alcohol also ends in OL and Phenyl ends
in "yl". In naming Organic compounds where
you have an R-group as a substituent, it ends
in yl. For example a CH3 is a methyl, a CH3CH2
is an ethyl, yl. The beginning of the word
the "phen" portion should hint benzene ring
and it's simply a question of what the benzene
ring looks like. The Phenol is a benzene ring
alcohol. That means we have a benzene ring,
a 6 carbon chain with alternating pi bonds
and an OH attached to it. That's it! it's
not attached to a bigger chain, it doesn't
have anything else coming off it. Phenol Alcohol,
but when you have just Phenyl that is the
benzene ring as a substituent on a larger
chain. So we'll show instead of an alcohol,
an R-group attached to it. If you have a giant
molecule with a benzene substituent,that substituent
is a Phenyl, yl substituent. Not to be confused
with the Phenol which is a benzene ring alcohol.
I hope this video helps you not only understand
but to look for functional groups but also
gives you couple of tricks to help you memorize
them. First thing I want you to do, give this
video a thumbs up and leave a comment below
letting me know if it helped you and which
mnemonic you like best then make sure you
visit my website leah4sci.com/Naming so that
you can download my FREE full color functional
group cheat sheet as well as try the Practice
Quiz. And then start working through the naming
series showing you how to tackle each functional
group including IUPAC and Common Names. The
link again is leah4sci.com/Naming.
