19. Aldehydes and Ketones:Nucleophilic Addition
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Let's talk about a solvent that likes to react with carbon eels. And that's water. So water loves reacting with carbon eels to make a molecule called Ah hydrate. But remember that Ah, hydrate is just a gem dial. Okay, Germinal, dial me there. Bulls attached to the same carbon. Okay, now the mechanism is pretty straightforward, guys, What winds up happening is that the lone pairs on the oxygen are attracted to the Electra Philip Carbon and you get the formation of a tetra hydro intermediate t i for short. Okay, What that's going to give us is a negatively charged oxygen and a positively charged water notice that the reason that this oh is positively charged because this is the water that came from here. And now it has one extra bond. Well, then, what you get is a proton transfer. So this step is called a proton transfer, where the o literally just grabs an h, plucks an h off of another part of the type of atrial. Intermediate. Now, if this looks unfamiliar to you, you haven't done a lot of proton transfers yet. Get used to it. Okay, A lot of these solvents that attack uh, carbon eels, They Some of them are gonna have proton transfer, so it's something that you should be aware of. Okay, so, guys, this is pretty interesting. So as I mentioned before, this means that if you're in lab and you mix, you have a 50% solution of two beauty known and that 50%. That means that if the other 50% is water, then it's not just gonna be the 50% water and 50% to beauty known. It's actually gonna be that you're gonna have some percentage in there is gonna be, ah, hydrate where the water is interacting with the key tone to make a gem dial. Okay. And you guys actually already might have experienced this because, um, in your biology lab, if you guys have taken by a one or two and if you've ever smelled those, like, nasty, like animals that they bring out for you to, like, cut open and look at sometimes you'll have to, like, maybe cut open like an earthworm or like, I don't know, like a bunny. I don't know, depending on animal cruelty. Regardless, there always soaked in what we usually call formaldehyde and formaldehyde we think has that nasty smell of, like, a dead thing that they're preserving. But actually, guys, when you're in lab cutting open that animal, it's actually not the formaldehyde that you're smelling its formal in. Okay, So formal in is the specific alga Hide the specific hydrate that's made from formaldehyde. When it reacts with water it makes formal in and formal in is what gives off that smell. So it turns out that you've actually already experienced the hydrate in your life, possibly. Or you will. If you take by one or two, you're going to smell these dead animals that are being preserved. And that is the smell of formal in which is ah, hydrate, not the smell of formaldehyde by itself. Now, guys, it turns out that this reaction is not really synthetically useful because the larger the are groups get, the more bulky that Tetra Hydro Intermediate is gonna be and the less favorite ISS. So the equilibrium is gonna be greatly shifted to the left, the greater the bigger that the are groups are. So as you're our groups get bigger and bigger, you're gonna have more and more original carbon eel and less and less hydrate. Okay, you can imagine that if you have a 10 carbon chain of both sides, it's gonna be very difficult in terms of stare, ICS, toe form a hydrate on. It's gonna be a much easier to keep it as a carbon deal. Okay, The only time that you would actually get a predominance of the hydrate is with an extremely small Carbonell like formaldehyde like we have here, where formaldehyde and water actually gives a majority of formal in. But it's because you have the smallest are groups possible, which is just ages. So in that case, it's favored. But if you have a larger are groups, then you're gonna usually shift towards the carbon deal in terms of your equilibrium. So let's do a mechanism, show the whole mechanism and then predict the equilibrium for the product. And then I'll show you the answer
Show the mechanism, predict the equilibrium
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so the mechanism was pretty straightforward. You would take your water, your oxygen, you would attack the Carbonell Carbon. You're going to get a Tetra Hydro intermediate that has an own negative. And in oh h two positive with an isopropyl and a fennel on either side. Then we know we're going to do a proton transfer, and that's going to give us our hydrate or which bleach, benzene and isopropyl. Okay, so not that hard now. It also asked for equilibrium. Now notice that I kind of messed up because I drew a forward arrow. It's not forward zero. It's an equilibrium arrow. So let's draw those in. So the equilibrium arrows for both of these steps would be shifted towards you think the right or to the left. What do you think is more favorite, the hydrate or the original ketone? So, guys, these are groups are definitely bigger than hydrogen. You know, they're pretty bulky, so the equilibrium is gonna be greatly shifted to the left, and only a tiny bit is going to go forward. Okay. In fact, it might be on the order of less than 1% hydrate. Okay, so that's why hydrates they're interesting toe, Understand? In terms of the theory of solvents attacking carbon eels, but synthetically, we don't really use thes because there's so in favor to form that. Really? You can't. You can't really get a stable gem dial out of it. The gem dial is gonna eventually go back, um, towards being a carbon. You Okay, So anyway, that's the end of this reaction. Let's move on to the next topic.
Additional resources for Hydrates
PRACTICE PROBLEMS AND ACTIVITIES (1)