Give the IUPAC name (including cis or trans, if needed) for ea...

Question

Give the IUPAC name (including cis or trans, if needed) for each of the following:

c. Chemical structure of a pentene with a double bond and a side chain, illustrating alkene naming conventions.

Accepted Answer

Hi, everybody. Our next problem says, provide the Iupac name of the given compound and include cysts or trans if necessary. And our compound is a six carbon ring with one double bond and the two carbons in the ring that have the double bond, each also has a methyl grip attached on the outside of the ring. Our answer choices are a cis 12 dimethyl cyclo two E B 12 dimethyl cyclo two C cis 12 dimethyl cyclohexane or D 12 dimethyl cyclohexane. So when we think about the name, our first step is always find the longest carbon chain. In this case, that chain is a ring. So we need to figure out how many carbons we have. So we're going to, I'll highlight in blue, I'll start at the top 123456. So if we didn't see from first glance, it was a hexagon, we have counted that there are six carbons in the ring and we have a double bond, how would we locate that double bond? Well, the double bond is the most important feature of this particular structure. So we would automatically start our numbering with the double bond. So we will call the first carbon in that double bond. And it doesn't matter which one that is because we have a symmetrical molecule. So I'll just use the one on top that would be carbon one and the other one would be carbon two. We don't need to number any further. We don't have any other substituents. Those are the only two we're interested in. So our double bond is from C one that's double bonded to C two. So let's think about the root name of this compound. We have a cyclo and then six carbons. So hex and then eene, since there's a double bond, do we need to put the number one in front of cyclohexane? No, we don't because by default, since we start with the most important thing, we would just assume that carbon one has the double bond. So it would be different if we had a chain and the double bond were on carbon two or carbon three where we couldn't start the numbering at the double bond since it's in the middle of the chain. But here, that's assumed we don't need to specify it. So we don't need a number there with that, we can already eliminate certain answer, choices, choice A and choice B say hex two E or psycho he two E for the name. And that too doesn't belong there. The carbon, the, the double bond would be labeled as carbon one. So you wouldn't have that too there. Um Note it's in the middle of the hexen. You might be surprised you might expect to see two hexen and that sort of thing. But the sort of newer Iupac rules prefer the number before the ene ending. So you'll see both ways in the middle of the word hexen or so like this hex two E or two hexen, but in either case, it doesn't apply to this molecule. So let's cross out A and B C and D both have cyclohexane as the root name. So now we just need to name the substituents and determine whether we need to label it cis or trans. So we have two methyl substituents and they are on carbons one and two. So C one C two. So it will be a dye methyl and on one and two. So one comma two dimethyl and there's a hyphen between the two and methyl. We use a comma to separate numbers a hyphen to separate a number from names. One, comma two hyphen dimethyl cyclo hexen. Now, let's evaluate, do we have cyst trans isomerism in this molecule? Well, let's recall the rule for that. So I put the rule in this little sort of cloud shape when we have a double bond and we've labeled it substituents as R one and R two on top of it, on the two different carbons, R three and R four on the bottom, on the two different carbons, cis trans isomerism is possible when R one does not equal R three and R two does not equal R four. So remember we have to keep straight. What cla classifies us as having cis trans isomerism as if each individual Carmen has two different substituents. So it doesn't refer to the substituents to the two different carbons. So R one can be the same as R two, R three can be the same as R four. But the carbon itself, each individual carbon must have two different substituents. So does that apply here? Carbon one has the ring on one side and the hydrogen on the other carbon two has the ring on one side. And the hydrogen, excuse me, not the hydrogen, they have a methyl group. So carbon one has the ring on one side and a methyl group on the other carbon two has the ring on one side and the methyl group on the other. So even though carbon one has the same substituents as carbon two on carbon one itself, these substituents are different. So we do have cis trans isomers impossible. Which is this, well, the methyl groups on the same side of the double bond, the ring is on the same side of the double bond. So this is a cis isomer. However, not. Our question says include cis or trans, if necessary, it's not necessary in this case, why is that a ring of six carbons cannot be in the form of a trans isomer that would put too much strain on the double bond. It couldn't loop back around and form a ring. You need to have at least eight carbons in your ring before you can have a trans isomer. So it's not necessary to include, this is a cis isomer. You don't need to include that in the name. So choice D is our answer. 12 dimethyl cyclohexane. Whereas choice C which says cis 12 dimethyl cyclohexane, excuse me. They also says cyclohexane. Um it's not that it's an incorrect description. It is s but it's not needed to put the cysts there because that's the only possible physical arrangement for this molecule. So once again, our answer here for the correct IAC name will be choice D 12 dimethyl cyclohexane. See you in the next video.

Give the IUPAC name (including cis or trans, if needed) for each of the following:
c.

Key Concepts

IUPAC Nomenclature

Cis-Trans Isomerism

Structural Representation

Watch next