Alcohol Reactions: Dehydration Reactions - Video Tutorials & Practice Problems
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concept
Alcohol Reactions: Dehydration Reactions
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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 H2SO4, reacting or reacts with an alcohol to form an alkene through 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 it 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 4 bonds. They each have lost a bond, 1 to hydrogen and 1 to Oh. 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. Remember, in a dehydration reaction we're just introducing sulfuric acid to our alcohol in order to lose water and form an alkene.
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Alcohol Reactions Dehydration Reactions Example
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Determine the elimination product form in the following 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, our alcohol carbon with its o h, and here are the neighboring carbons. This neighboring carbon here is making 2 bonds, so it has 2 hydrogens. This neighboring carbon here has makes 2 bonds, so it has 2 hydrogens we don't see. In this process we're gonna lose water, so lose an O H 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 2 hydrogens. So here we're gonna lose water, and when we lose water that's gonna force those 2 carbons to make a double bond with one another, in order for them to continue to make 4 bonds. So our alkene would look like this, and this would be cyclohexene. This would be our elimination or dehydration product.
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concept
Zaitsev’s Rule
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Now Zaitiff's rule, the loss of water follows Zaitiff's 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 Zaitin's rule, we're going to say the o h 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 2 hydrogens, and the other neighboring carbon has 3. Following Zaitiff's 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 o h from the alcohol carbon, so it's gone. We'd lose an h from this CH two group so now it's just CH, and they need to maintain their 4 bonds so they'd form a double bond between each other. So again, we utilize Zydtief'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.
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Alcohol Reactions Dehydration Reactions Example
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Here it says, determine the elimination product formed in the following reaction. Alright. So we have our alcohol carbon right here, with its o h group, and we have our neighboring carbons. This c h and this c h three. They have different number of hydrogens, which means we're going to utilize Zaitiff's rule. Remember under Zaitiff's rule, it's the neighboring carbon with fewer hydrogens that loses an H. So this carbon, the CH Carbon on the left has only 1 hydrogen, the methyl carbon has 3. So we're gonna lose an h from the c h group. So now our product will look like this. We'd still have c h 3 here, still connected to this c, connected to this c h 3. 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 cause it's only losing an Oh, and it's still connected to this CH3. This would be the alkene or elimination product formed within this reaction.
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Problem
Problem
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
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Problem
Problem
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
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