The following names are all incorrect. Draw the structure repr...

Question

The following names are all incorrect. Draw the structure represented by the incorrect name (or a consistent structure if the name is ambiguous), and give your drawing the correct name.

a. cis-dimethylpent-2-ene

b. 3-vinylhex-4-ene

Accepted Answer

Hello everyone. Let's do this problem. It says show the structures represented by the incorrect names below and write the correct Iupac names part A S two S four hex A 24 E, part B two methyl, one allele, trans ethene. OK. So first we need to draw the structures. So we are going to convert these names to the structures. And I always like to do that by reading the name from right to left because we see the root name at the right hand side or the end of the name and the substituent groups and configurations come before that. So start with the root at the end and move backwards. Then once we have that structure, we want to rename it and we are going to do that by following the Iupac naming rules. So first we want to find the longest continuous carbon chain and we want that to include any alkenes or Alkins, right? I saw the suffix E. So I know we're going to have some alkenes here. So we want to include that alkene in our parent chain. Then we are going to number that chain and we want to number it closest to the alkene. So starting with the alkene carbon if possible. And we want to make sure we give our substituent the lowest numbers possible. OK. Then we're going to list our substituent with their locus or the carbons that they are located on. And lastly, we will note the configuration if any is needed, such as R OS configuration for chiro carbons or EZ configuration for alkenes that are tri substituted, at least, if not substituted with four carbons. OK. So let's do this. So starting with S two S four, hex A 24 E. So Hex tells me we have a six carbon chain, 12345624. E tells us we have two double bonds on carbons, two and four and SS two S four tells me that both of these double bonds are going to be c which means that the highest priority group is going to be on the same side. So notice that on the, on either side of each double bond, we have a carbon group and a hydrogen, right? And when I say the same or opposite side of these double bonds, we draw a line across a double bond like I call it the fence. So we want our largest groups or our groups with the highest atomic mass to be on the same side. So automatically I see the hydrogens are on opposite sides here. So that needs to change, right? We need our carbon groups to be on the same side. So our structure will look something like this. 1234, 56. OK. So there is our structure but now we need to name this correctly. OK. So we have Hexane is the parent chain, right? A six carbon chain. And there are two double bonds. So when we have two double bonds, we name it hexad dyne, but we put the location of those double bonds before the suffix dye. So we have hex a 24 dyne. OK? Now, there are no other substituent but we need the configuration is naming these alkenes and sis. Correct. No, we name them E or Z, right? So it's similar to CS and trans, but for naming, we use Enz and since there are more than one configuration, there is more than one configuration applied here, we need to specify which configuration belongs to which al let me review what E and Z mean first. So E means that the high priority groups are on opposite sides of the fence. And Z means that the high priority groups are on the same side of that fence. OK. So since they are on the same side of the fence, in both cases, we have Z configuration for both two and four carbons, two and four. So we have two Z four, Z hex A dying. So that is the correct name for this structure. All right, let's move on to part B we have two methyl, one allele, trans ethane. So ethene is a two carbon alkene. Then we will have a methyl at carbon two and an allele group at carbon one, which is going to be 123 more carbons. And we will have a double bond between those first two carbons, right? So the carbon that is connected to the rest of the parent chain is one carbon away from that double bond. OK. And let me rotate this. So it looks more correct. OK. So let's name this compound correctly. So Ethane is not our parent chain, right? We have a longer continuous chain here. 123456 carbons. So that is going to be hexane, but we have two double bonds. So again, hex ady this time, those double bonds are on carbons, one and four. So we have hex A 14 dying and we don't have any other substituent groups. What about configuration? Well, the alkene at carbon one is only monos substituted with a carbon group. So we are not going to specify any configuration there, but the alkene at carbon four is di substituted. Sorry, I think earlier, I said it must be tri substituted, but it is di substituted. But the important part is if it is di substituted, those groups have to be on either side of on different carbons, right? So we have a carbon group and hydrogen on carbon four carbon group. And hydrogen and carbon five and those carbon groups which are higher priority are on opposite sides. So this is going to be e configuration. And since it is the only one with configuration here, we don't need to specify its location. So this will be E hex. So 14 dying, let me redraw that. So that is it for this problem. I hope this video is helpful and thanks for watching.

The following names are all incorrect. Draw the structure represented by the incorrect name (or a consistent structure if the name is ambiguous), and give your drawing the correct name.
a. cis-dimethylpent-2-ene
b. 3-vinylhex-4-ene

Key Concepts

IUPAC Nomenclature

Cis-Trans Isomerism

Alkene Structure and Substitution

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