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.

(e)

Accepted Answer

Hi, everyone. Let's look at our next question. It says classify the isomerism in the pair of molecules shown below. And our first molecule on the left has a nitrogen with three ethyl groups attached to it. And the one on the right, we have a carbon in the center with two ethyl groups and then one ch two NH group attached NH two group attached to it. Our answer choices are A and an timmers B ditherers C conformers or D constitutional isomers. So we can recall that an isomer is a molecule that has the same molecular formula as its isomer. So as it's other, the other molecular comparing it to, but something different about its arrangement and space. And the first question you ask when seeing what type of isomer is this is, are the atoms connected in the same way? Do they have the same bonds? Are they bonded to the same atoms in each molecule? No, no. That that's the first question we ask if we already know we have isomers which the way our question is structured, we do know that the question says classify the isomerism and all of our answer choices are types of isomers. We don't have anything like these are not isomers or none of the above. So we don't need to double check if we were on a test or something, we will touch on that briefly just to be thorough. But note the way this is phrased, we can assume we have isomers with the same molecular formula. So are the atoms connected in the same way is the bonding the same. And that's pretty obvious to look at that. No, it is not in the first molecule. Our nitrogen has three carbons attached to it. And the second molecule, our nitrogen has one carbon and two hydrogens. So very glaring differences here in connectivity and when the answer to this question is no, then we have constitutional isomers. So same atoms, same numbers of atoms. So that's choice. D here is our answer but connected in a different way if the answer is yes. So just to be thorough here and look at why our other answer choices are wrong. So yes, then we move on. So first we look at so yes, they're connected in the same way, they just have a different arrangement in space. Then our next question is, are they mirror images? And if that answer is no, then they are ditherers. So they have the same connectivity, different arrangement in space, not mirror images. That's choice B ditherers. But again, not our answer choice because we've already said no, they aren't connected in the same way, if they are mirror images and they are not super imposable. So you've drawn your mirror image and there's no way you can rotate it to make it match up with its original. Then they are in Antium. But again, not our answer choice. That's a and anti emmers because again, the connectivity there is the same. And then the final question you would look at is if these are identical other than rotation around a sigma bond. And this is a bit of a funny definition because as we know sigma bonds have free rotation. So two conformers choice C which is the term for that are not really isomers in the sense that it's essentially the same molecule since it can flop around does it freely. But it's sometimes important for the sake of a reaction mechanism or thinking about the different ways a molecule can exist in space to be able to draw those different conformations. So that's why we have a term for it. But again, they're essentially identical molecules. So choice C also not correct because it has the same connectivity. So the isomerism that's present in this pair of molecules is choice d constitutional isomers. And that's our answer. Now, I'll just touch briefly if we had a question that involved our needing to calculate the molecular formula from this line angle structure. I will use red, I like to mark in dots, all my carbons you can write out the entire structure writing out where there's carbons and hydrogens, but that takes a lot of time and space. So I prefer, I know that on this structure, the end of every line segment is a carbon. So I'm just kind of highlighting it with little red dots so that I don't miss anything because obviously it can be easy to overlook one. So I see in my first molecule where I have these, I even if I think to myself, I have three ethyl groups. Each one has two carbons. So I've got six carbons. So C six would be the first part of that. Now, I need to look at my HS. So again, they're implied in this structure. They're not written down and I'm just going to jot a number by each carbon to indicate how many hydrogens it has. Again, just a little less space than writing out each, each time. So every terminal carbon has three hydrogens. So put that on there and then my internal carbons on those ethyl groups have two hydrogens. So I've got three carbons with three hydrogen. So nine, three carbons with two hydrogens. So 69 and six is 15. So H 15. And last of all, I've got this low nitrogen. So put in an NC six H 15 N. Now, if I look at my other molecule first, put a red dot on every end of every line segment for my carbons, I've got two ethyl groups with two carbons each. So that's four plus one, central carbon is five plus one carbon bond to the nitrogen is six. So, c six, now, the hydrogens, I might be a little worried were different because two of them are now on this nitrogen. But if I number them again, so three on my two terminal carbons and then two written on the carbons that are secondary, have two bonds to them. And then I've got one central carbon that's tertiary. It's got three carbons bond to it bonded to it. So it only has one hydrogen. So we've got two, threes. So three and three is six, then three twos. So that's another six makes 12. My one on the central carbon is 13. But don't forget those two hydrogens on the nitrogen, it makes 15. So H 15 and then my n so you could see that my molecular formulas here c six H 15 N are identical. They are indeed isomers just in case you wanted a little review on that. 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.
(e)

Key Concepts

Isomerism

Structural Isomerism

Stereoisomerism

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