—
Functional groups? Functional groups within functional groups? Hank takes today’s Crash Course video to discuss some confusing ideas about Hydrocarbon Derivatives, but then makes it all make more sense.
—
—
Transcript Provided by YouTube:
00:00
The smell of cinnamon and rotting cadavers…
00:02
Compounds that can remove nail polish, power a car, knock you unconscious, or make your headache go away.
00:07
All of these things can be accomplished by simple organic compounds with different functional groups sticking off of them!
00:13
Yes, I said functional groups! We will be talking about them a lot today.
00:16
Now, when chemists started studying this stuff,
00:19
they didn’t always know what really made one chemical different from another.
00:22
Only that certain compounds, though different, often behave similarly.
00:26
Some smelled like fish, some had relatively high boiling points,
00:29
some reacted in similar ways with the same compounds.
00:32
Now, however, we know better!
00:33
We know what they are, where they come from, and why they act the way they do.
00:36
We are DEEP in the knowledge of organic chemistry’s most powerful tools!
00:41
It feels good in here!
00:43
So dive in, join me in this solution of ethers and esters and aldehydes and amines and alcohols,
00:48
but, like, not literally because that would be super gross and you would probably die.
00:53
[Theme Music]
01:02
Thus far, we have only discussed organic compounds involving carbon and hydrogen and nothing else.
01:07
And yes, carbon and hydrogen are the backbone of organic chemistry.
01:10
In fact, 1-, 2-, and 3-dimensional combinations of carbon atoms are the backbone of most organic compounds.
01:16
But today we’re going to throw a couple of newcomers into the mix,
01:18
two of my very favorites: oxygen and nitrogen.
01:22
Using these two extra elements, we’re going to talk about seven exciting and different functional groups.
01:27
But first, what is a functional group? Sounds super boring.
01:32
Well organic chemistry is the architecture of chemistry.
01:35
With it, we don’t just study chemicals, we build them.
01:37
And we know that certain groups of bonded atoms function in very specific ways.
01:41
Since we know how these functional groups function, we (and by we I mean the human race)
01:46
can add to or modify or remove and join them together in predictable ways.
01:51
And thus, we can build the compounds we need, whether it be the simple stuff, like acetylsalicylic acid, aspirin,
01:56
or something more complicated, like alpha-(5,6-dimethylbenzimidazolyl)cobamidcyanide,
02:01
better known as vitamin B12. Neat, right?
02:03
When we talk about functional groups, we get so focused on those small areas of the molecule,
02:08
that the rest of the molecule doesn’t actually matter that much.
02:11
So we use “R” to represent the rest.
02:14
R just represents any fragment of organic molecule that we’re not super concerned with at the moment.
02:19
We also sometimes call the area of unconcern the “R group”
02:22
as opposed to the “functional group” where the business is getting done.
02:25
So now that I’ve been talking at you for like, three minutes,
02:28
let’s actually look at what kind of trouble nitrogen and oxygen can get up to in an organic compound.
02:32
The first and most familiar oxygen-based functional group is the alcohol, a terminal “-OH”.
02:38
Not terminal in that it will kill you, though ethanol can kill you,
02:41
and other alcohols like methanol absolutely WILL kill you, but terminal in that it ends a carbon chain.
02:47
Now, what happens when you dehydrogenate an alcohol?
02:51
Not when an alcohol dehydrates you — that would be a hangover — but we dehydrogenate it.
02:56
In a chemical reaction, removing the hydrogen from the oxygen and creating a double bond to the carbon.
03:01
That dehydrogenated alcohol is an aldehyde, literally from “alcohol dehydrogenated.”
03:06
Alcohols and aldehydes have a lot of similar properties because of the electronegativity of the oxygen.
03:10
Hydrocarbons on their own are actually pretty dang boring.
03:13
Checking out our electronegativity chart,
03:14
you can see that the difference in electronegativity between C and H is only 0.35,
03:19
so there’s no real regions of negative or positive charges in the molecules.
03:23
Therefore, these simple hydrocarbons are pretty nonpolar
03:25
and their electrons are distributed evenly over the molecule, which is why, you know,
03:29
oil and water don’t mix.
03:31
Adding those oxygens mixes stuff up.
03:33
Electrons start clumping, the oxygen-hydrogen bond of an alcohol is fairly polar,
03:37
with a difference in electronegativity between “O” and “H” of 1.22,
03:42
so the oxygen gets a delta minus (δ-) and the hydrogen gets a delta plus (δ+).
03:45
Not only does this make alcohols and aldehydes more likely to be soluble in water,
03:48
but it completely changes the kind of chemistry you can do with them.
03:51
Impending confusion alert!
03:53
There can be functional groups inside of functional groups.
03:56
We’ve already seen two of them.
03:58
If an OH is part of a larger functional group, we’ll refer to it as a Hydroxyl,
04:02
and if a carbon double bonded to an oxygen it’s part of a larger group, we call that a carbonyl.
04:06
For example if we have a carbonyl bonded to a Hydroxyl, that, my friends, is a Carboxylic Acid.
04:13
Hopefully you’re getting the hang of the lingo.
04:15
Just looking at this Carboxylic Acid thing, if you think about the electronegativity of those two oxygens,
04:19
you can imagine that that hydrogen there is gonna be pretty weakly held.
04:22
And so it can dissociate in solution, making it an acid.
04:25
Carboxylic Acids are the acid part of amino acids, which make up proteins,
04:29
which make up, you, so they’re pretty important.
04:31
The simplest carboxylic acid, commonly known as Formic acid, is what makes fire ant bites burn,
04:36
and just one more carbon and you get Acetic acid, or vinegar,
04:39
which, even in a diluted solution you have in your cupboard, is not something you want to get in your eyes.
04:43
Now, Acetic acid is also interesting because once upon a time,
04:46
a clever chemist called Leopold Gmelin did some chemistry
04:49
and knocked off the OH group and joined the carbonyl with another carbon.
04:52
The result was a non-terminal, or internal, carbonyl.
04:56
He named that stuff ‘acetone’, meaning basically ‘derived from Acetic acid’.
05:00
Now, acetone is just a name of that one chemical, not the functional group itself.
05:04
To get that, we knock the ‘A’ off and harden that ‘C’ into a ‘K’ and get a ‘Ketone’.
05:08
So yeah, when we have a carbonyl in the middle of a carbon chain, that is a ketone functional group.
05:13
Acetone has a ketone group and it’s called ‘acetone’ because it was derived from acetic acid,
05:17
which is vinegar, the most common carboxylic acid in your kitchen.
05:20
I swear, if you watch this episode twice, you will understand.
05:23
Acetone, with that big hunk and double bond is nice and polar, so it’s water soluble; great for cleaning stuff.
05:30
The hydrogen bonds between that oxygen and those outer hydrogens are enough
05:33
to keep the molecules bound together so it’s not gaseous at room temperature.
05:37
It’s also stable enough that it isn’t very toxic.
05:39
In fact, there’s a little bit of acetone in your blood right now,
05:43
which is why it’s safe enough to use as nail polish remover.
05:45
It is, however, unstable enough that you don’t want to get it near any open flames.
05:49
Now we only have two more oxygen-based functional groups that we’re gonna talk about,
05:53
These are groups that have internal oxygens bonded directly to carbons.
05:57
When you see it now in the middle of the chain like this it’s either an ether or an ester,
06:00
either ester or ether, ether or ester, either one, one or the other, either ether or ester.
06:06
Ethers have just one oxygen all alone in the middle of that carbon chain.
06:09
Esters, on the other hand, I focus on that ‘S’ noise, making me think it must be plural,
06:13
because they have two oxygens: one in the middle of the chain and one as part of a carbonyl.
06:17
Esters are just like a ketone mixed with an ether.
06:20
In fact, if you look at all these oxygen based functional groups you’ll see that they’re all very closely related.
06:24
Aldehydes are just dehydrogenated alcohols, ketones are just aldehydes bonded to R-groups on both sides
06:29
(instead of a hydrogen on one side).
06:31
While carboxylic acids are ketones bonded to an OH group instead of an R group,
06:35
and ethers are just alcohols bonded to an R-group instead of a hydrogen.
06:38
Now I did promise you some nitrogen at the beginning,
06:40
and I apologize to all of you die-hard nitrogen fans for having given you none so far.
06:44
Let’s just say that the amine is ever so simple, just a terminal NH2 group.
06:48
Remember, ammonia is NH3, so that “am” from ammonia gets stuck onto that amine group.
06:53
Amines are super stinky: two of my favorites are putrescine and cadaverine.
06:59
And yes, they are found in abundance in rotting carcasses of animals and yes, they smell super terrible.
07:04
And those are the seven functional groups that we’re going to talk about.
07:07
It was super fun, for me anyway, but I am, I admit, kind of a huge dork.
07:12
Organic compounds that include these functional groups have various wonderful names:
07:15
wood alcohol, cinnamaldehyde, and cadaverine.
07:18
It’s lovely, right? Well chemists want more out of their names than wit and charm. They’re too clever for that.
07:24
Which is why, next week we’ll be talking about how to figure out how to name these compounds,
07:29
and if we have the name, how to figure out what the compounds are.
07:33
Thanks for watching this week’s episode of Crash Course Chemistry.
07:35
If you were paying attention, you learned that alcohols are organic compounds with hydroxyl groups,
07:39
if you dehydrogenate them, the hydroxyl converts to a carbonyl
07:43
and they become dehydrogenated alcohols or aldehydes.
07:46
If a carbonyl bonds to a hydroxyl, the functional group becomes acidic and it becomes a carboxylic acid,
07:52
the most common of which is acetic acid, which if you switch the hydroxyl out for a methyl group,
07:57
becomes acetone and if that ‘C’ were a ‘K’ noise, it’d be a ketone, which is what acetone is.
08:03
Finally, a carbon chain with an internal oxygen is either an ether or an ester,
08:07
and it’s only an ester if it’s bonded to a carbonyl.
08:09
And of course, anything with an NH2 group is an amine.
08:13
This episode of Crash Course Chemistry is written by me, Hank Green, edited by Blake de Pastino.
08:17
Our Chemistry Consultant is Dr. Heiko Langner.
08:19
It was filmed, edited, and directed by Nicholas Jenkins.
08:22
Our script supervisor was Michael Aranda, who is also our sound designer.
08:24
And our graphics team is Thought Cafe.
Up next
—
This post was previously published on YouTube.
—
Photo credit: Screenshot from video