Identify the following pairs of structures as structural isomers, cis–trans isomers, or the same molecule:
a.

Question

Identify the following pairs of structures as structural isomers, cis–trans isomers, or the same molecule:

a. Chemical structures illustrating isomer pairs, labeled for identification as structural or cis-trans isomers.

Accepted Answer

Welcome back, everyone. Let's look at the next question, consider the following pair of structures and we have two condensed structural formulas. We'll talk about them more in just a minute. And then our question says, determine whether they are identical molecules structural isomers or cyst trans isomers. And our answer choices are a identical molecules. B structural isomers or C cis trans isomers. So let's look at these two structures. Well, the first one's written all in the form of a straight line, we have H two C double bond ch and then CH two CH two CH two CH three. Our other structure is written in sort of a zigzag fashion. So we have CH three dash CH two and then a bond going down to CH two dash ch two A bond going down to CH which has a double bond to CH two. So it can help to draw out the second structure in a straight line. So we can analyze whether it's the same or an isomer of the first. However, the first thing to note is when we look at this double bond in both molecules, we have H two on one side of the double bond. And we recall that when we think about cist trans isomers, and I've drawn a sample double bond here with our groups of R one and R two on the top R three and R four on the bottom. And a cyst trans isomer is possible if R one does not equal R three and R two does not equal R four. So if the R groups on the sides on each side of the double bond are not the same. In this case, in both double bonds, we have two hydrogens on one side. So those are identical and there's no Crans isomerism impossible. So when we look at our answer, choices, choice C cyst trans isomers cannot be correct because there's no cyst trans isomerism in either molecule. So we've eliminated that possibility. So now we need to see are they identical or are they structural isomers recall that structural isomers have the same molecular formula, but the atoms are attached differently. Maybe you have different branches for instance. Well, it's a little hard to tell with this second structure written in a different way. So let's stretch it out in a straight line with the double bond on the right side to compare the two side by side. So it can help us also to count our carbons here. So when I look at my first structure, I see I have 123456 carbons in the chain. When I look at my second structure, 123456 carbons as well, both have the double bond at the very end. So already, we know we've got no substituents six carbons in the chain double bond at the end. So even without writing again, we can be pretty sure these are identical. If I were on a test, I'd go ahead and pick choice a identical molecules. But just to be thorough here, let's write it out, look at them or not side by side, but top and bottom. So I'm going to rewrite my second structure right underneath my first. So I'll start with the double bond. So I'm starting from the bottom of the second structure. I have H two C double bond CH and then I have 1234 C, two groups in a row which is just the same as my top structure and then finishing off with ach three. So when I look, I can see these two are identical molecules, they are not structural isomers. We can cross out choice B because they are not attached differently, they're exactly the same. So our two structures here are choice a identical molecules. See you in the next video.

Identify the following pairs of structures as structural isomers, cis–trans isomers, or the same molecule:
a.

Verified video answer for a similar problem:

Key Concepts

Structural Isomers

Cis-Trans Isomers

Same Molecule