Alcohol Reactions: Dehydration Reactions - Video Tutorials & Practice Problems

Alcohol Reactions: Dehydration Reactions

In this video, we're gonna take a look at alcohol reactions and in particular dehydration reactions. Now, under dehydration reaction, this type of reaction has sulfuric acid which is H two. So four reacting or reacts with an alcohol to form an alkene to the loss of water. Now to form the double bond, the alcohol carbon loses its oh and its neighboring carbon loses an H atom. If we take a look here at this example, question or example reaction, we have our alcohol here. We're introducing our sulfuric acid. Here goes my alcohol carbon with its oh group and we have this neighboring carbon and this neighboring carbon, both of which happen to be methyl groups. They're both the same. So we can lose an H from either side. I decide to show it losing from the left side. But could also happen to the right side since they're the same. So here we're going to lose water. The water we lose is over here. And remember, carbon must continue to make four bonds. They each have lost the bond one to hydrogen and 1 to 0 they need to replace that bond they've lost. So their only option is to make a double bond to one another. So that's why we make an alkene as our product. So remember in a dehydration reaction, we're just introducing sulfuric acid to our alcohol in order to lose water and form an alkene.

Alcohol Reactions Dehydration Reactions Example

Determine the elimination product form in the fall reaction. Now, another name for a dehydration reaction is an elimination reaction. Here, we have our alcohol reacting with sulfuric acid. So we know we're trying to create an alkene at the end, here is our carbon or alcohol carbon with its oh and here are the neighboring carbons. This neighboring carbon here is making two bonds. So it has two hydrogens. This neighboring carbon here has, makes two bonds. So it has two hydrogens. We don't see in this process, we're gonna lose water. So lose an oh from the alcohol carbon and lose an H from one of its neighboring carbons. Here, I decide to lose it from this side, but it could equally happen on the other side because those two neighboring carbons are the same, they both have two hydrogens. So here we're gonna lose water. And when we lose water, that's gonna force those two carbons to make a double bond with one another in order for them to continue to make four bonds. So we al keen would look like this and this would be cyclo hexen. This would be our elimination or dehydration product

Zaitsev’s Rule

Now, Zito rule, the loss of water follows Zito rule when we undergo an elimination or dehydration reaction of an alcohol. Now, it's used when the neighboring carbons have different numbers of hydrogens. Under Zito's rule, we're going to say the oh atom is lost from the alcohol carbon and the H atom is lost from neighboring carbon with fewer hydrogens. If we take a look here at this reaction, we have an alcohol that is not symmetrical. Here, we have our neighboring carbons, one neighboring carbon has two hydrogens and the other neighboring carbon has three following Zeus rule, we would lose an H from the carbon in red. Since it has fewer hydrogens to lose. When we do this, we'd still lose the oh from the alcohol carbon. So it's gone, we'd lose an H from the CH two group. So now it's just ch and they need to maintain their four bonds. So they'd form a double bond between each other. So again, we utilize Zito's rule when our neighboring carbons next to the alcohol carbon have different number of hydrogens. This is just a way of us making sure that we're making the correct alkene at the end.

Alcohol Reactions Dehydration Reactions Example

Here, it says, determine the elimination product formed in the following reaction. All right. So we have our alcohol carbon right here with its O age group and we have our neighboring carbons. This CH and this CH three, they have different number of hydrogens, which means we're gonna utilize Ziff's rule. Remember under Zus rule, it's the neighboring carbon with fewer hydrogens that loses an H. So this carbon, the ch carbon on the left has only one hydrogen. The methyl carbon has three. So we're gonna lose an H from the CH group. So now our product will look like this. We still have CH three here still connected to this C connected to this CH three. It loses its H in order to make a double bond with the alcohol carbon, the alcohol carbon has lost its oh and then that alcohol carbon still has its h because it's only losing an oh and it's still connected to this CH three. This would be the alkene or elimination product formed within this reaction.

Determine the name of the alkene product formed in the following dehydration reaction.

• A. $cis-1-heptene$
• B. $2-heptene$
• C. $1-heptene$
• D. $trans-1-heptene$

Determine the name of the alkene product formed in the following dehydration reaction.

• A. $1-methylcyclohexene$
• B. $4-methylcyclohexene$
• C. $2-methylcyclohexene$
• D. $3-methylcyclohexene$