Hemiacetal and Acetal Formation - Video Tutorials & Practice Problems

Hemiacetals and Acetals Concept 1

Now, here we can say that aldehydes and ketones react with alcohols to form heals and acetyl. Now, what exactly is a hem oyl? Well, a hemy is a compound with a hydroxy group. So, oh and, and our Coxie group a war on the same carbon atom. Now, when we say R here R is just a placeholder that represents carbon. This R could be a methyl group. It could be an ethyl group. It could be a ring, it could be a more complex ring. It could be a long chain. It's just a placeholder for a carbon group. If we take a look here, we're starting out with this aldehyde, it reacts with this alcohol. And what we create is a carbon that has both an oh group and an or group attached to it. So we've just created a hemmy, a seal or hemi acetal depending on how you want to pronounce it. Now, what is a full acetyl or acetyl then? Well, that's just the compound that possesses two oxy groups on the same carbon. Now, this hem acetyl that we've created could react with another mole of an alcohol that causes the replacement of this oh group with an or group. So now you have a carbon connected to two or groups. So what you have here is an acetyl or acetyl as your final compound. So just remember aldehydes and ketones can both react with alcohols. If we react with one mole of alcohol, we create this hemi acetyl that hem ayl can then react with a second mole of an alcohol to give us a full acetyl or acetyl compound.

Hemiacetals and Acetals Example 1

Identify each of the following compounds as an acetyl or hem acetyl. So remember an acetyl group is when we have a carbon connected to two or groups. And a hem acetal is when we have a carbon connected to an oh group. And an or group. If we take a look here, look to see where carbons are connected to, to oxygen. So we're looking at this carbon here, we're looking at this carbon here. We're looking at this carbon here and then this carbon here. Now if we take a look at the first one that carbon in red, what is it connected to? It's connected to an oh group and an O carbon group which is or remember R here is just a placeholder for carbon group. That carbon group could be methyl ethyl or long chain or rink. So here we have an oh and we have an or so this is a hemi acetyl or hem acetyl for the next one. What do we have? Same thing? We have an oh group and an or group connected to that carbon. So this is also a heme ay for scene that carbon is connected to two or groups. So it's a aceto or acetone. And then here this last one, we have an oh group connected to it and an or group. So it's a hemi. So this is how we characterize or classify each one of these four compounds within this example. Question.

Formation of Hemiacetals and Acetals Concept 2

Now, when it comes to the formation of hem ays and acetyl, we're going to say that one more alcohol produces hem ays and two moles. Alco alcohol produce aces. If we take a look here, we have an aldehyde and we have a ketone, both of them react, let's say with one mole of an alcohol doing this will help change those allies and ketones into hem ays. Now, how does this work? Well, we're going to say here that this carbon carbon is this alcohol carbon just like here and here we're gonna say the alcohol, the or portion of the alcohol will provide the or portion that attaches to my formerly known as carbon carbon. So the or portion of this alcohol is what's attaching here to, what was the carbon carbon? And then we can say here that the oxygen that was the carbon carbon gets converted into an oh group. That's the way you have to look at it. So the or portion of the alcohol attaches to the carbon carbon and then the oxygen that was double bonded becomes an oh group. Now, if we decide to add another mole of alcohol, so we add a second mole of alcohol to both of these heals. The same thing would happen again. Now, now the or portion of this alcohol is what's going to attach to? What was my carbon on carbon? Well, remember, carbon can only make up to four bonds. It can't go up to five bonds. So forward to attach the oh groups have to go away. And that's what happens. And that's why at the end we have two or groups attached to, what was my carbon carbon? That's the whole process, we react one mole with these als and ketones and we stop at the hem acetyl. But once we introduce a second mole of alcohol, they continue further to make a full acetyl acetyl compound. Right. So, keep that in mind when it comes to their formations.

Formation of Hemiacetals and Acetals Example 2

He says, draw the structure of the aceto aal formed in the following reaction. All right. So we're starting out here with a hem a hem ace or hem acetyl and we're reacting it with our second mole of an alcohol. Remember that the or portion of the alcohol is what's going to attach to this carbon here in order to do that though, the 08 group has to go because Karma can only make up to four bonds. Introducing this or group from the alcohol would be introducing 1/5 bond, which is not possible. So something has to leave the oh, is the group that would leave at the end? What do we have? We have that carbon which already had this or group attached? It's still attached. And now we have a second or group from this second mole of alcohol being attached. So this would represent my acetyl or acetyl product, right? So this would be our final answer.

What would be the product of the following reaction?

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Draw the intermediate in the following reaction.

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Draw the structure of the product when one mole of cyclopentanone reacts with two moles of methanol in an acidic solution.

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