So, this is the part that can get a little bit tricky if you don't have everything mapped out already. It turns out that different types of alcohols and carbonyls on sugars respond differently to periodic acid. It's not like a one size fits all, that it's always an aldehyde. It's actually not. You have to kind of do a little bit of memorization here. So, what I've done is I'm trying to organize it for you in the easiest way possible so that you're going to just be able to look at this chart and know exactly what to do. Just to repeat, you can't just guess what the product will be. The product is very specific depending on what type of alcohol or carbonyl you're starting with.

So, what I'd like to start with is basically the difference between an aldose and a ketose. Okay, remember that most sugars always come in either the form of an aldose or a ketose. Remember, an aldose at the top is going to have an aldehyde. Remember, a ketose at the top is going to have a ketone, and that's what I've just drawn here. Okay. Well, that oxygen that's either in the aldose or the ketose will react with periodic acid. Now, this isn't the same exact reaction as the vicinal diols reaction because this is not an alcohol. It's a carbonyl, but it still is going to oxidize that carbonyl. Okay? So how would we oxidize these carbonyls?

Well, if you're starting off with an aldehyde, what you're gonna wind up getting at the end is, and I'm going to say this a lot, formic acid. Now, formic acid is the common name for this molecule. You could also call it methanoic acid, which would be the IUPAC name, but most commonly it's called formic acid and that's just the simplest carboxylic acid possible. It's a carboxylic acid that only has one carbon. So if you have an aldehyde at a terminal end, well, aldehydes are always terminal, you're going to get formic acid as your oxidation product.

Now if you start off with a ketone, for a ketose at the top, then you're not going to get formic acid, you're actually going to get CO₂. So I'm just going to put here CO₂. We all know that's carbon dioxide. So you can see that in both cases, we're oxidizing. We're adding more bonds to O, but the exact products are a little bit different.

So, everyone got that so far? We've got formic acid. We've got CO₂. But now we have to look at the alcohols. Those are the carbonyls, but what about the alcohols? Well, if you have an alcohol, that is an internal alcohol. What do I mean by internal? There are things on both sides, so it has something on the top and something on the bottom. What you're going to wind up getting from that is also formic acid. You're also going to get one equivalent of formic acid for every internal alcohol that you have. Okay? Cool.

And let's say you have a terminal alcohol. Now by the way, this terminal alcohol I drew it as if it was the bottom, but we know that terminal alcohols could also exist on the top because maybe you have a ketone on the top, so then you have an alcohol there. That's fine. Whenever you have a terminal alcohol, your product is going to be this, which is the condensed formula for it is CH₂O, which is also known as formaldehyde. Oops, let's try that again. Formaldehyde, and we know that formaldehyde is the simplest aldehyde. Okay. So, you're either going to get the smallest aldehyde or the smallest carboxylic acid, or CO₂, carbon dioxide. Okay?

So, that's what you need to know, and if you know these four cleavage patterns, then you should be able to take any molecule, react any sugar, sorry, any monosaccharide, react it with periodic acid and predict exactly what products you're going to get. Okay. So why don't we go ahead and do an example of this together to get our practice in figuring out what the products would look like.