Which of the following substances exist as can cis–trans isomers? Draw both isomers for those that do.
a. 2,3-Dimethyl-2-pentene (condensed structures only)
b. 2-Methyl-2-hexene (both condensed and line structures)
c. 2-Hexene (line structures only)

Question

Which of the following substances exist as can cis–trans isomers? Draw both isomers for those that do.

a. 2,3-Dimethyl-2-pentene (condensed structures only)

b. 2-Methyl-2-hexene (both condensed and line structures)

c. 2-Hexene (line structures only)

Accepted Answer

Welcome everybody. Let's take a look at our next problem. It says, identify the substance that can exhibit cis trans isomerism. If the substance exhibits isomerism, draw both isomers and we have three different compounds. A B and C for A, we have two methyl, two pine and it says both condensed and line structures. So if we have isomers, we will need to draw both forms of this. So let's draw two methyl, two pine. So I usually like to start with line structures. I find them a little bit simpler, a little less bulky. So we know with our brief exp P that we have a five carbon chain, our E tells us we have a double bond with the number two saying it's on carbon two. So we'll draw our five carbon chain 12345, our double bond goes from carbon two to carbon three. So put that in there and then we know we have a methyl substituent on carbon two. So we'll draw that methyl group in. So then we have to say, does this exhibit c trans isomerism and draw both types of structures if we need to draw isomers? Well, as we look at our double bond here and the substituents for it, we can see that we have two identical substituents. Two methyl groups, essentially, one is the end of our five carbon chain and one is our named methyl substituent that are identical. So, got this too identical our groups on our double bond. If two R groups are identical, on the side of the double bond, we have no cyran isomerism for this molecule because however, we drew the other side, it would end up being the same molecule that you could just rotate around and they would match up. So choice A does not exhibit C trans isomerism. We'll just highlight that in yellow and move on to choice B. So let's label that A because we're gonna start running out of space. So for choice B, we have three hexen, those draw line structures only for our isomers. So I'll start with a line structure. I have hex E. So I have six carbons. So we'll start there 123456, our double bond is on carbon 3123. So between three and four and we have no substituents. So does this exhibits this trans isomerism? Well, we'd need to look at our, our groups off of our double bond. On this side, we have a branch with 12 carbon. So we have an apple substituent essentially on the left side, on the other side, 12 carbons. So we have another ethyl group on the right side. And then we have our two hydrogens. Well, we have two ethyl groups. We have different r groups on the two sides of the bond ethyl and hydrogen ethyl and hydrogen. So we can have this trans isomerism in this situation. It's going to erase the HSS since we're supposed to draw line structures. So we don't want HS on them. So we have line structure number one. And in this case, the two ethyl groups are on opposite sides of that double bond. So this would be the trans isomer. So let's draw the cis isomer with both groups on the same side of the double bond. So in this case, we'll start the same way, our first two carbons are double bond coming from carbon three to carbon four. But now, instead of the ethyl group being on the opposite side, we need to draw it coming up so that both ethyl groups are on the same side of the double bond and then finish the rest of it. So this is our cis isomer with both lethal groups on the same side of the double bond. So we found our substance that has cyst trans isomerism in three hexen. So let's move on to C 23 dimethyl, two hexen. This is condensed structures only I am going to start with a line structure just because again, I like that as a less bulky way to just see where the connections are between my different groups. So two hexen, I've got my six carbon chain, 123456, my double bond going from carbon two to carbon three that in there. And then we have methyl groups on carbon two and carbon three. So right away, what do I see? I see that I have two identical methyl groups on one side of my double bond, the end of the chain and my substituent on carbon two. So these two groups are identical. And when we have two identical groups on the same side of the double bond, we have no cyran isomerism for this. So let's look at our answer here. Now, our problem tells us to draw both condensed and line structures for choice A and condensed structures only for choice C. Now it's a little bit confusing since whether we're supposed to draw that no matter what or only if they have isomers. But to be thorough, let's just draw a quick condensed structure for both of them. So choice A again, we only need to draw one version because we have no isomerism. We'll draw our double bond here. CC double bond on one side, we know we have two methyl groups. So we have CH three and CH three coming from the left side of our CC double wand. On the right side, we have an ethyl group and a hydrogen. So we'll make this C but we want to indicate how these groups come off of the double bond. So we'll go ahead and make our h coming down and then coming up from the carbon, we have our ethyl group. So ch two, CH three. So this way of drawing can sometimes help us see how things are arranged around the double bond. Again, there's no cis trans isomerism because of these two identical groups here, looking at choice C, if we want to draw a condensed structure, we'll start with our cc double bond in the middle. We know we have our two methyl groups on the left side, on the right side, we'll have a methyl group. I'm drawing it coming down. But again, we could draw it either way since there's no cyst trans isomerism and then coming up, we have 123 carbons. So ch two ch, two ch three coming up on the right side. So we have our summary, we have only one that exhibits cis trans isomerism that is B the three hexen draw the line structures only. So we have our line structures for our trans isomer and our cis isomer choice A we show no is trans isomerism. And we drew the condensed structure just to be thorough along with the line structure choice C, we also have no Crans isomerism, but we drew the condensed structure of our one version here as well. So I'll just highlight the condensed versions here and there we have our answers see you in the next video.

Which of the following substances exist as can cis–trans isomers? Draw both isomers for those that do.
a. 2,3-Dimethyl-2-pentene (condensed structures only)
b. 2-Methyl-2-hexene (both condensed and line structures)
c. 2-Hexene (line structures only)

Verified video answer for a similar problem:

Key Concepts

Cis-Trans Isomerism

Alkenes and Their Structure

Drawing Isomers

Which of the following substances exist as can cis–trans isomers? Draw both isomers for those that do.a. 2,3-Dimethyl-2-pentene (condensed structures only)b. 2-Methyl-2-hexene (both condensed and line structures)c. 2-Hexene (line structures only)

Verified video answer for a similar problem:

Key Concepts

Cis-Trans Isomerism

Alkenes and Their Structure

Drawing Isomers

Which of the following substances exist as can cis–trans isomers? Draw both isomers for those that do.
a. 2,3-Dimethyl-2-pentene (condensed structures only)
b. 2-Methyl-2-hexene (both condensed and line structures)
c. 2-Hexene (line structures only)