Give the IUPAC name for each of the following:
b.

Question

Give the IUPAC name for each of the following:

b. Structural formula of an alkyne with carbon and hydrogen atoms, showing triple bond and branching.

Accepted Answer

Welcome back everybody. Our next question says, give the systematic name for the structure below. And we have a condensed structural formula which says H three C with a single bond to ac with a triple bond to another C the single bond to AC which has ACH three and an H bonded to it. And a single bond, single bond to ach with AC L substituent with a single bond to ach with ach two ch three branch and then a single bond to ach three. Our name possibilities are choice. A five Chloro six ethyl, four methyl, two hep B five Chloro 46 dimethyl, two oc dime C three chloro two ethyl, four methyl, five hep or D four Chloro 35 dimethyl six OC time. So our first step is always to identify. So find the longest carbon chain. We see we have a triple bond. So it needs to include that triple bond. So let's do that. First, I'm going to use a blue highlighting to go through the carbons and count them. My structure is written as sort of a straight line of carbons with substituents coming off. So we'll just start left to right, and then see which way of counting gives us the longest carbon chain. So starting from the left, I have 12, there's my triple bond 34. Now I have an alternate of a branch or to continue, but my branch is only a methyl branch. So I want to continue going straight 56. Well, now I have the choice of continuing straight to 1/7 carbon or up into the branch on the sixth carbon, which is an ethyl group, it has two. So going up into my branch, sort of turning a corner on the structure, the way it's drawn gives me a longer chain than continuing straight. So that was carbon six. Let's go into what looks like an ethyl branch and make that carbon seven and carbon eight. So instead of having an ethyl substituent, that's become part of my main chain and my substituent is now the methyl group that looks like the end of the chain because if I counted the other way, I would only have seven carbons. So my main chain here is eight carbons. I now need to number it so that the triple bond is on the lowest number. So the lowest numbered carbon, that's because my triple bond is my most important sort of main functional group here in this chain. So forget all the other substituents. We're usually looking for the lowest substituent number. The triple bond is the most important one in terms of my numbering. So we always remember with a chain, we could start numbering from either end. However, we can see right away that triple bond is way over to the left on only the second carbon. So it's pretty obvious which direction we need to start from. So we start from the left carbon one and then right away carbon two is where our triple bond is. So we have an eight carbon chain with a triple bond from C two. So we have C two with a triple bond two, C three. So we can come up with our base chain name based on that, we have a triple bond. It's going to end in Iyne, we have eight carbons. So our number prefix will be oct. So this is an oct time and with our triple bond going from C two to C three, we will label this to hyphen oct time to label the location of the triple bond. Well, on a test, this is a long molecule. It will take a lot of working through, but we have multiple choice options. So it's worth looking at the choices at this point to see if you can eliminate some just based on the proper longest chain name. So let's look at our answer choices, looking for a two hyphen oct time. So choice A says to Hep DNE. So this is incorrect. So we can eliminate choice. A right away. Choice B does say to OCT time. So that's correct. Choice. C says five hep. So incorrect and choice D says six OC time. So it's got the correct OC time, but the incorrect labeling of where the triple bond is. So that would be if we had numbered the other way, if we counted from right to left, 123456, the triple bond would have been in carbon six. So it's not that it's saying the triple bond is in the wrong place. You could label it from there. But by convention, we want the triple bond to have the lowest number. So choice D is incorrect. Oh, I forgot to cross out choice C which was a Hept. So just with that longest chain name, we already know the only option that can be correct is choice B but this is a practice problem on a test, I'd be done. We're going to be a little more thorough. So we have our base chain name. We need our substituents. So what are our substituents? Well, we have a methyl group and then we have what looks like the end of the chain, but it is another methyl group. So we have two methyl groups and then we have one chlorine group or one chlorine atom. So those are our sub total number of substituents and we just need to label where they are. So we have the numbering we're going to use. So let's just go ahead and number all of our carbons, we'd started 12, carbon three, the other end of the triple bond four. And there's one of our methyl groups. So one is on carbon four. Then carbon five, there's our chlorine group. It's on C five, six. Carbon six is where we turn the corner. And so carbon six has the other methyl group. So our second methyl group is on C six. So how do we name those substituents? Well, our two meals on four and six. So we'll say four comma six, we separate numbers with commas and then hyphen to separate the numbers from the names. We have two meals. So we have die metal and then our one chlorine. So it doesn't need a prefix, one carbon five. So we have five hyphen Chloro. And how do we decide what order these go in? Well, it's in alphabetical order. It's, I'll put ABC next to here. ABC order, ignoring any prefixes. So the dye does not count. Although either way our Chloro will be first. So our name in its proper order, we start with the chlorine by alphabetical order. So five hyphen Chloro, then a hyphen now are meals 4, 6 hyphen dimethyl and then another hyphen and then our two hyphen oct time and we double check. That is the name given in choice B so you can see on our other answer choices. Some of the mistakes came from numbering the carbons in the wrong order, numbering them as a straight chain including that last methyl group. Instead of adding on the two more carbons in what looks like an ethyl substitute. You can see at least one has labeled the ethyl substituent. So those are common mistakes to make when naming something like this. But our correct answer is choice B five pleural 46 dimethyl two oct time. See you in the next video.

Give the IUPAC name for each of the following:
b.

Key Concepts

IUPAC Nomenclature

Functional Groups

Structural Representation

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Give the IUPAC name for each of the following:b.

Key Concepts

IUPAC Nomenclature

Functional Groups

Structural Representation

Watch next

Give the IUPAC name for each of the following:
b.