What type of isomerism is indicated by each of the following p...

Question

What type of isomerism is indicated by each of the following pairs of molecules? Be as specific as possible.

(d)

Accepted Answer

Welcome everybody. Let's look at our next problem. It sis identify the specific type of isomerism indicated by the following pair of molecules shown below. And our first molecule, we have a central carbon that's a tertiary carbon. It's got two TERT beetle groups attached to it and an alcohol group. And the second molecule that central carbon has a methyl group instead of the alcohol group. And on the right hand side, what was a terp beetle group now has an alcohol instead of a methyl on its middle branch. So essentially the alcohol and a methyl group have swapped places on our molecules. Our answer choices are A and anti ers B ditherers C constitutional isomers or D conformers. So first of all, what's important to note is we've been told given the way this question is phrased that these are isomers. Our question says, identify what type of isomers they are. Our answer. Choices are all types of isomers. We don't have any option. That's like choice D not isomers. So we don't need to go through the bother. We recall isomers are characterized by having the same molecular formula. So if we were presented with a different format where it may be said, identify at the r isomers. You would have to count all the different types of atoms on these structures to double check that they have the same molecular formula. So I'll touch base on that at the end, you can skip it if you wish. But if you want a little reminder of how to do that, but again, given the way our question is structured, we can take it as a given they have the same molecular formula. So the first question, I want to notice when identifying types of isomers is are the bonds the same in terms of are the same atoms connected to each other. So does carbon one have three hydrogens on both molecules is the oxygen on carbon four in both molecules. So not just the same types of atoms, but the same individual atoms is that connectivity the same. And if the answer is no, then we have a constitutional isomer. So same molecular formula, same amount of every atom but connected in a different way. So when we look at our, at our, look at our molecules here, we can see that they must be constitutional isomers because they're not connected the same way. In the first molecule, the alcohol group is connected to that central carbon. So I'll put a little red dot on it. And the second, the ox, the alcohol group is connected to that carbon. That's a terminal carbon on the right side in that tt beetle chain. So with our oxygen, our methyl groups have swapped places, they're not connected to the same atoms. So our answer choice is then choice c constitutional isomers. Every other type of isomer here, an anti or dium or conformer has the same connectivity. Constitutional is the one type that's bonded in a different way. So let's just look briefly at these other types to remember what they are and why they're incorrect. Well, why they're incorrect is they're connected the same way. But let's just touch briefly on them. Choice. A and Antium are non superimposable mirror images. So you draw a mirror image of your molecule and then see, can I rotate it in any way to make it identical to the original image like a left and right hand, if they are not superimposable, then they are an an tumors. But again, can't be our answer choice since they have the same connectivity, then B ditherers are the ones that are connected in a different geometry, different arrangement in space but not to different atoms. So they have a different arrangement in space, but they're not mirror images. So if I were going step wise, I'd say OK, they're connected the same way they have the same bonds. Yes. So they're dimers and then look at are they mirror images to move on to see if they're an anti MERS. Finally choice D conformers are the most similar of all they are essentially identical but differ only in rotation around a sigma bond. So as we can recall, sigma bonds freely rotate in space unlike pi bonds or triple bonds. And so they the same molecule since that is a free rotation. But sometimes if you're looking at reaction mechanisms or just understanding why a molecule might do something, it might be useful to distinguish the different places. A group could be when you rotate around your single bond. So that's what a conformer is. But obviously, that's not what we're looking at here. So choice D is incorrect. So once again, our isomers here because they have different connectivity or choice c constitutional isomers. Now you can stop here or if you just want a brief review of checking the molecular formula, keep listening and I'll go over that very quickly. So, on our line angle structure here, one tricky thing is that our carbons are not written out as seas. Our hydrogens aren't shown at all, they're implied. So when we're looking for the molecular formula, oxygen's easy, we've got 10 we see it there, oxygens always have to be designated and the hydrogen on our alcohol group is shown specifically, don't forget to add it on at the end, I'll start with my carbons then and you could draw out a structure where you ride out every carbon hydrogen that takes a lot of time and space. I kind of like putting dots at every sort of junction on the structure which represents a carbon. I'm using red here to make them stand out. So I don't miss any and then I can count the dots. There's a little risk maybe of overlooking something, but it's just a lot faster and takes up less space than writing everything out. And I can look for those dots. So I see I have in terms of my carbons, I've got the two chart beetle groups which as their name indicates, have four carbons each. So four plus four is eight. And then I've got my central carbon. So I have C nine and then I need to look at my hydrogens. Now for hydrogens, they're implied here. I'm just going to write a little number indicating the number of hydrogens by every carbon. So again, a little takes up a little less space than writing out every single atom. So my terminal carbons all have three hydrogens. So we'll put a three at the end of every methyl group. Then on my tuttle groups, the central carbon of the tuttle has four bonds. It's got three methyl groups on a central carbon, no hydrogens there. And then my central carbon atom is tertiary. It has three bonds. So it has one hydrogen plus, don't forget the alcohol hydrogen. So that gives me nine hydrogens on each tuttle group. So nine plus nine is 18 and then I have one in the center and one on the alcohol. So I've got a total of 20 hydrogen. So C nine H 20 then my one lone oxygen C nine H 20 0. Now let's look at the isomer over here. So again, if I put dots this time, I'll use green since I've got a green dot there already and put dots on all my carbons. And now it's a little different. I have four and one tuttle group. The other group since the methyl group has been replaced by alcohol has just three carbons. So four plus three is seven plus my central carbon is eight. And then I now have that methyl group of the central carbon is nine. So C nine, that's the same terms of hydrogens, write a three for every metal group. So I've got nine on the left plus six on the right gives me 15 plus three. And that methyl group that got moved is 18 plus my central carbon which still has one. So that's 19 and the one on the alcohol is 20. So H 20 then of course, my single oxygen. So you can see they both have the same molecular formula C nine H 20 0. See you in the next video.

What type of isomerism is indicated by each of the following pairs of molecules? Be as specific as possible.
(d)

Key Concepts

Isomerism

Structural Isomerism

Stereoisomerism

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