How many isomers can you write that fit the following descriptions? See Worked Example 12.12 for guidance.
c. Alcohols (―OH) formed from 2-methylhexane

Question

How many isomers can you write that fit the following descriptions? See Worked Example 12.12 for guidance.

c. Alcohols (―OH) formed from 2-methylhexane

Accepted Answer

Hi, everybody. Welcome back. Let's look at the next problem. It says count the number of isomers that will fit the following description, alcohol formed from 234 tri methyl pentane A six B four C three or D two. So first, we want to draw the structure of our molecule. So we can think about how many isomers we could form. So we have a pentane. So we have 12345 carbons and then we have methyl groups on carbons 23 and four. So a key thing to note here when thinking about possible isomers is that we have a symmetrical molecule. So we're going to have some duplicate arrangements where adding something on a carbon on one side will result in an identical molecule if we add on the carbon on the other side. So I'm going to go ahead and number these carbons so that I can keep straight where I might add things. So my main chain, I will number them one through five. And then just for convenience sake in terms of thinking about my alcohol possibilities, I'm going to label the three methyl methyl on carbon two as a the methyl on carbon three as B and the methyl on carbon four as C to keep them straight. So let's think about where I could add an oh group to create an alcohol. Well, I could start with carbon one, I could add an oxygen on carbon one. So I'm going to keep from getting confused. I'll make a separate structure over on the side to draw this particular molecule. So if I add an alcohol and carbon one, I've made one isomer and what I'm going to do is go ahead and highlight in blue that this is a unique isomer. I've made highlight that carbon one in blue. So we'll go through each of our carbons and make sure they're each accounted for whether they create a unique isomer or not. What we're calling this molecule symmetrical. Is there another carbon where I'd add the alcohol? Excuse me, that would result in an identical molecule? Well, yes, there is. And I'm going to highlight it in red to show that it doesn't make a new isomer. If I added an alcohol group to carbon five, I would have the identical molecule as I have when I add it to carbon one again, due to that symmetry. So I'm a again indicating in red there to show I've considered that carbon but ruled it out since it doesn't make a new isomer. So let's keep on going. Well, let's what would happen if I added an alcohol group to carbon A, the methyl group on carbon two. Well, I might be tempted to think that makes a new isomer, except that when I look at the geometry around carbon two, essentially, I have two methyl groups, I have carbon one is just one more carbon at the end there. So the I have another plane of symmetry surrounding or sort of a local plane of symmetry surrounding carbon two. So I would have the same molecule if I put the alcohol group on carbon one versus carbon A. So carbon A is going to get a red highlight as well. It it's not one that will create a new unique isomer. For the same reason, carbon sea can be ruled out on the other side. So no new isomer for any of those. Now, let's think about carbon two. Well, that would be a unique arrangement. So let me go ahead and highlight that in blue to show us another isomer and just to keep track, we will draw that structure. So we can indeed see that it's a new isomer. I'm just going to erase that methyl group and move it over a little bit there. So it's not that al alcohol group added on to that carbon A but on to carbon two itself. And as you can see that is a different structural isomer than the one I have already do. I have a symmetrical arrangement on the other side. Yes, I do because carbon four is a symmetrical carbon. So I can rule out carbon four is not making a new isomer. Finally, I could be aware that I would have two unique isomers due to the two carbons in the middle. So I could add an alcohol group on carbon three. So let's draw what that would look like. Put my structure up there again and I could add my alcohol group right here in carbon three. As you can see that is definitely a different molecule than I have already. And finally, I can add that alcohol group two carbon B, the methyl group on carbon C or the methyl methyl group on carbon three, excuse me. And again, there's no matching carbon or no opposite carbon since that's right in the middle of the molecule. So there's nothing symmetrical there oops just stick that alcohol group onto the methyl group on carbon three. So I can look back at my initial diagram and see I have four blue blue highlights, four isomers possible. My other carbons as indicated by red highlights will make molecules that are identical to ones that I've already made. So our answer for the number of isomers is possible to create is choice B four possible isomers. See you in the next video.

How many isomers can you write that fit the following descriptions? See Worked Example 12.12 for guidance.
c. Alcohols (―OH) formed from 2-methylhexane

Verified video answer for a similar problem:

Key Concepts

Isomers

Alcohol Functional Group

Structural Representation

How many isomers can you write that fit the following descriptions? See Worked Example 12.12 for guidance.c. Alcohols (―OH) formed from 2-methylhexane

Verified video answer for a similar problem:

Key Concepts

Isomers

Alcohol Functional Group

Structural Representation

How many isomers can you write that fit the following descriptions? See Worked Example 12.12 for guidance.
c. Alcohols (―OH) formed from 2-methylhexane