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Video Solution: (b) Neomenthol is a stereoisomer of menthol. That is, it has...

Problem

(b) Neomenthol is a stereoisomer of menthol. That is, it has the same constitution but differs in the arrangement of its atoms in space. Neomenthol is the second most stable stereoisomer of 2-isopropyl-5-methylcyclohexanol; it is less stable than menthol but more stable than any other stereoisomer. Write the structure of neomenthol in its most stable conformation. 

Video Transcript

Hey everyone. So, here we're dealing with 2 different structures, we have menthol and neo menthol. Now, in case you don't really know what that is, let's actually draw the IUPAC name for them, so IUPAC would call these 2-isopropyl 5-methyl and then cyclohexanol, okay? So now you guys can understand what these two compounds are, right? Now, cyclohexanol would look like this, we have a six membered ring with an OH position two, we have an isopropyl and over here at position 5 we have your regular methyl group. Now, looking at their chair confirmations, we know that in chair confirmations equatorial is the more favored position or the more stable. So, one conformation would be menthol, right? Because menthol. Notice that's chair conformation all of our substituents are equatorial. So, in that our neo menthol this is going to be the next in line, so it's not the most stable but is the second. So, looking at all of our groups, which one is going to be the smaller group? because remember that the bulkier groups are always going to prefer to be equatorial, what that means is that this bulky isopropyl group here, we rewrote it as Ch CH3, 2, that one's going to stay equatorial, which other group do you think would want to stay equatorial, so that this neo methol is the second most stable form, our OH or our CH3? which one do you think is going to essentially take up more room? Well, notice that we have 4 atoms two atoms, right? We have a CH3 2 an OH, what that means that our CH3 is a more bulky substituent and it's going to want to stay equatorial as well. So, here we have CH3, what that means is that are now our OH is not going to be equatorial anymore that's going to be forced to go axial, so this is what neo menthol looks like it. So, told you that it's the second most stable form. Now, menthol, we explained is the most stable form that has all the groups equatorial. So, in order to make it the second more stable form our neo menthol must take the least bulkier substituent and make down the axial, so now the relationships change a little bit. Now, our OH and our isopropyl have a cis relationship because they're facing the same direction and our OH and our methyl group have a trans relationship, but notice that before our OH and our isopropyl had a trans relationship and our other two groups had a cis. Alright, so I hope this made sense, let me know if you have any questions.

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