So we already know that base is the ability to remove the alpha hydrogen of a monosaccharide and that's the same exact step for the enediol rearrangement because remember the enediol rearrangement has to get to the enediol intermediate. So that means that the first few steps of this reaction are exactly like epimerization. So my OH comes in, grabs the alpha hydrogen, forms a double bond, kicks electrons up to the O. What I wind up getting is a double bond with a negative charge where stereochemical information has been lost from carbon 2. And we know that to get to the enediol we're going to have to protonate, so let's go ahead and do that. We're going to protonate with the conjugate acid of water. And that's going to give us our enediol. Okay? And then we know beyond that that if we then just go backwards throughout the whole mechanism that we just did and deprotonate that H, we can go and epimerize C2 to get mannose. Let's show how that happens once again. You would then use OH− and just pull that H right back off to form a negative charge here, double bond, and then we would use water to protonate the alpha position because you reform the carbonyl. The double bond grabs the H and kicks off the OH and what we wind up getting is D-mannose. So this whole process that we just did was just epimerization. Okay? But it was epimerization specifically through the enediol mechanism. Okay?

Now this isn't the only thing that you can do with an enediol because what if the base instead of grabbing the top proton, what if it grabbed the second proton? What if it grabbed the proton off of carbon 2? Would that change the product? Actually, it would change it very significantly. So let's see what would happen if instead of grabbing the top one, we grab the bottom one. If I grab the bottom one and formed a negative charge, it's going to need 2 arrows. Let's just do this real quick. OH−. I grab the H and then the H gives its electron charge and an H, and guys, this is an enolate once again, but now it's the other enolate, okay? So now it's possible to just regenerate that double bond and get rid of it. So basically what I could do is I could take my water and I could use this negative charge here to make the double bond and protonate the alpha position. So basically everything that I did with this enolate would happen with this one, but now it's happening with the double bond being reformed on C2 instead of C1. Notice how in the enolate above for the epimerization, C1 reformed the carbonyl, but for my bottom enediol, C2 formed a carbonyl. So what that's going to do is it's going to give me a double bond here now, an H that's attached an extra H that's attached to here and this blue H is still here. Okay? So what we just did is we just turned D-glucose, which is an aldohexose into, we just turned it into a ketohexose, D-fructose because we were able to us