Using the alcohol shown, draw all the possible alkenes that might be formed on its dehydration. Which do you think will be the major product(s)? Which do you think will be the minor product(s)? It is alright to have more than one major and minor product.

Question

Using the alcohol shown, draw all the possible alkenes that might be formed on its dehydration. Which do you think will be the major product(s)? Which do you think will be the minor product(s)? It is alright to have more than one major and minor product.

Accepted Answer

Hi, everybody. Let's take a look at our next question. It says, consider the structure of the alcohol shown below. Draw all the possible alkenes that can be formed from the dehydration of the alcohol. Identify the major and minor products. There can be more than one of each type of product. So we have this alcohol here and the carbon that the alcohol is attached to is a tertiary carbon. It has three different substituents. So it has substituent one which is an ethyl group, substituent two, which is a methyl group and substituent three, which is an isopropyl group. So, since a dehydration reaction occurs when we remove the hydroxy group from one carbon and the hydrogen from an adjacent carbon, we have three possible alkins. Now we do want to double check, we have to have at least one hydrogen on those neighboring carbons. So we double check. Yes. On the ethyl group, the neighboring carbon will have two hydrogens on the methyl group three and on the isopropyl group, it will have one. So obviously, if there's no hydrogen on that adjacent carbon, it can't have that dehydration reaction. But in this case, there is so we have three possible alkins to evaluate which is major and minor. We remember that the major pro product will be the most substituted alkene as that will be the most stable alchem. So let's think about what these three possibilities are. We'll start with first dehydration reaction occurring on the carbon in the R one group. So the ethyl group, we're going to highlight the carbon in red and then I will draw its hydrogen. So we keep in mind that we're eliminating the hydroxy group and the hydrogen on that carbon. So let's draw that product. We would have our first cc single bond and then we have AC C double bond. So that's our, I'm going to highlight in red, that was a carbon that lost its hydrogen and then in blue or carbon that it had the alcohol group on it. So we keep going drawing our structure that carbon, the blue carbon has a methyl group attached to it and then it still has the isopropyl group. So that is alkin number one. So put number one here for all. Key number two, I'm going to go ahead and erase my markings here, my hydrogen and my highlighting. So now actually I'll le I should leave the blue highlight for the carbon that has the alcohol group because that will stay the same in all three cases. Our our group number two is that methyl group. So in this case, our red carbon would be at the end, the one on the methyl group. So we're going to eliminate the hydrogen from that carbon. And in this case, our double bond will be on that one short little branch. So we have our ethel branch, this is our blue carbon. So it now has a double bond with just one carbon from the methyl branch. So that will be our red carbon at the end of that double bond. And then we continue with our isopropyl branch coming off. So that's keen number two. And then finally, we have our third possible product. So I'll erase my red highlight, but leave my blue highlight there. Again, it's the same carbon that had the alcohol. And in this case, I'll remove the hydrogen from the carbon at the center of the isopropyl group. So let's draw that alkene number three, I have my Ethel branch. Here's my blue Carmen that had the alcohol group. It still has a methyl group, but now there's a double bond with two methyl groups coming off of it. And that's the red carbon there that had its hydrogen removed. So now we have our three possible alkenes, but we need to identify the major and minor products. So we need to look at how substituted these double bonds are in alkene. Number one, we have three R groups coming off our alkene and one hydrogen. So we have three substituents in alki. Number two, we have just two substituents. The two branches since this was a methyl group just coming off on its own. So this one has two substituents. And then finally, in alkene, number three, we have four substituents, we have a fully substituted alkene. So in this case, structure, number three will be the major product, well structured. Number one and two will be the minor products as they are less substituted alkenes. So we have our three possible structures based on me, three possible double bonds that can form from our tertiary alcohol. And we know that the first two are minor products while the third is the major product. See you on the next video.

Using the alcohol shown, draw all the possible alkenes that might be formed on its dehydration. Which do you think will be the major product(s)? Which do you think will be the minor product(s)? It is alright to have more than one major and minor product.

Verified video answer for a similar problem:

Key Concepts

Dehydration Reaction

Zaitsev's Rule

Regioselectivity