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- We've done several videos now on amines, which I forgot to
- mention, and this is probably the most fun notion about
- amines, is that they tend to be smelly.
- Let me write this down.
- Amines tend to be smelly.
- And I can make the smelly smell a little bit.
- And in general, in their gaseous state, they'll often
- smell like ammonia, so it's a very strong smell, or in their
- liquid state, they usually smell like fish,
- or even dead fish.
- They smell like fish.
- And, in particular, if you look at trimethylamine, so
- this is-- let me draw it like this.
- H3C, you have your nitrogen.
- You have CH3 and then you have your CH3.
- And you can even draw the lone pair.
- This is trimethylamine.
- This is the fish smell.
- This right here is the fish smell.
- Now, the whole reason why I brought this up is because in
- this video, we're going to introduce a new type of
- molecule, and that's an aldehyde.
- And I want to contrast their smells.
- Now, some of the smaller aldehydes still have a pretty
- strong smell, in particular, formaldehyde.
- And we'll talk a little bit more about
- why this is an aldehyde.
- So this right here is formaldehyde, and that's the
- common name.
- And you've probably seen it used as a kind of
- preservative.
- Maybe even in your biology class, if there's like a dead
- frog in a solution, it's probably inside of
- formaldehyde.
- Let me write this down.
- Formaldehyde.
- Once again, this is the common name.
- I'm going to teach you in a second how to systematically
- name these things.
- But when you have larger aldehydes, they actually can
- have a pretty sweet or even a rosy smell.
- So you have something like benzaldehyde, which you
- actually saw when we started the benzene derivatives.
- So this is benzaldehyde right over here.
- Let me write this down.
- This is benzaldehyde.
- And then this molecule here, just when I tell you what it's
- called, you'll probably guess what it smells like.
- So this has a benzene ring like this.
- And then you have one, two, three carbons.
- The last one's double bonded to an oxygen and then a
- hydrogen like there, and they have a double
- bond right over here.
- And this is called cinnamaldehyde.
- And as you could guess, this smells like cinnamon.
- And, in fact, this is the molecule in cinnamon that
- gives it its smell, although you don't want to have large
- quantities of it or it might be poisonous.
- But in cinnamon, it's a very pleasant thing.
- So larger aldehydes tend to have kind of a nice, rosy,
- sweet, flowery smell.
- The smaller ones tend to be kind of pungent.
- If you open up that jar in your biology class and smell
- that frog, it will not be a pleasant smell.
- So now that I've talked about smell enough, I think, let's
- talk about what makes an aldehyde an aldehyde.
- And you might even see a pattern here.
- In all of these aldehydes that I've drawn, we have a carbon
- double bonded to an oxygen.
- And actually, this part of it right here, and we'll see this
- over and over again, this is called a carbonyl group.
- So that is a carbonyl group.
- This right here is a carbonyl group.
- And you even see it over here.
- But that by itself is not the distinctive
- feature of an aldehyde.
- You'll see that in other types of molecules.
- Let me write it here.
- Carbonyl.
- What's distinctive about an aldehyde is, attached to the
- carbon in the carbonyl, you have a hydrogen.
- And sorry, I forgot to draw this hydrogen here on
- benzaldehyde.
- You have a hydrogen here.
- So, in general, an aldehyde is something
- that looks like this.
- You have a carbonyl group.
- You a carbonyl group.
- You have a hydrogen, and then you just have some other type
- of carbon chain.
- This right here is the simplest possible aldehyde,
- and actually, this chain ends up being
- just another hydrogen.
- Now, these three that I've shown right here, these are
- their common names, and these are the way that most people
- will talk about formaldehyde, benzaldehyde, or
- cinnamaldehyde, so they're just kind of good to know.
- And I'll show you one more.
- And this is a pretty important one.
- Let me do it down here so we have some space.
- So another one looks like this, so bonded to a CH3 over
- here and then a hydrogen.
- This right here is called acetaldehyde.
- And I just wanted to expose you to these common names
- because this is what people normally
- use for these molecules.
- Now, there is an IAPUC-- I always forget the acronym.
- There is a systematic way to name them.
- It's actually pretty straightforward.
- You just look at the longest carbon chain, and you always
- start numbering at the carbon that's in the carbonyl group.
- And it's always going to be at the end of the chain because
- that's always going to be bonded to a hydrogen.
- Actually, let me just make clear that
- this is also an aldehyde.
- You have your carbonyl group, and on one end, you have a
- hydrogen, just like that.
- Now, the systematic way of it, you just look at the longest
- carbon chain.
- Over here, there's just one carbon.
- So here, you would call this, the systematic name, you would
- call this methanal, not methanol.
- Methanol would mean you would have an OH group.
- But since you have this double bond and you have a hydrogen,
- or you could say this double bond is at the end of the
- carbon chain, this is an aldehyde.
- So the systematic name is methanal, not methanol.
- Let me make that clear.
- This is methanal right there.
- This one, I won't do cinnamaldehyde or
- benzaldehyde, because this is really the only way that
- people name them.
- Actually, frankly, formaldehyde, people never
- call it methanal.
- And acetaldehyde, they'll never call it what I'm about
- to name it, but the systematic name is, the longest carbon
- chain, you have one, two carbons, so it is ethanol.
- Ethanal, I don't want to pronounce it incorrectly.
- So let's do a couple more of these, just to make sure we
- have a decent understanding of the systematic names here.
- And in general, if you have a really long chain, the
- systematic names are what is used.
- So this thing right here, what would you call it?
- It's clearly an aldehyde.
- You have a carbonyl group, a hydrogen, and you have one,
- two, three carbons.
- So three carbons, the prefix is prop-, so it's propanal.
- It's an aldehyde.
- If we want to do something slightly more complicated,
- let's do something like this.
- What would this be called?
- Let's see, we have one, two, three, four, five.
- We have five carbons.
- So it will be pent-.
- Penta-, and then it's obviously an
- aldehyde, so it's pentanal.
- And you always assume that you start numbering at the carbon
- in the carbonyl group, so one, two, three, four, five.
- And on the two carbon, you have a methyl group.
- So this is 2-methyl.
- So you have a methyl group right here.
- So this is going to be 2-methylpentanal.