Now recall that an alkyne possesses a carbon-carbon triple bond. And we're going to say here that the set of rules for naming alkynes are very similar to the ones for alkenes. Here though, the modifier is we're going to change the ending from '-ane', coming from an alkane, to '-yne', because we're dealing with an alkyne. Now, a good thing here is that alkynes, because they have a triple bond, do not possess cis or trans isomers. Here in terms of our naming convention, we'd still have to give the location, the numerical location of substituents; we'd have to give the location of our triple bond in our structure, and again we'd have our modifier where we change the ending from 'ane' to 'yne'. So keep that in mind when we start naming different types of alkynes.
Naming Alkynes - Online Tutor, Practice Problems & Exam Prep
Rules for Naming Alkynes Concept 1
Video transcript
Naming Alkynes Example 1
Video transcript
It says, "Determine the systematic name of the following alkyne." So to do that, we're going to employ the following steps. Step 1, we're going to find the longest carbon chain, which represents our parent chain, and assign a name according to the prefixes and modifier. Now, the parent chain should include a triple bond, and have the greatest number of carbons. If there is a tie along this chain, choose the chain with more substituents. Step 2, you would assign names to all the substituents.
Alright. So first, let's look at what the longest chain could possibly be. I need to make sure that the triple bond is within that longest chain. So we have here, what? 1, 2, 3, 4. Yes. There's a carbon here and a carbon here next to the triple bond. 5, and then we could go 6, 7. If we did that, that would give us what? That would give us 2 substituents. But is there another way we could number this? Could we go 1, 2, 3, 4, 5, 6, 7? That is also a 7 chain, alkyne. 7 Carbon Chain Alkyne. But look, how many substituents do we have now? 1, 2, 3. This way gives us more substituents, and it also gives us the longest carbon chain as well. So this is the correct way to go. So we're gonna say that our longest carbon chain that includes the triple bond and gives us the most substituents would be this way. Alright. And we've determined who the substituents are. There's this one carbon here which is a methyl. This one carbon here which is also a methyl. And then 2 carbons here which is ethyl.
Start numbering the chain from the end closest to the triple bond. Assign the location to the first triple-bonded carbon. Alright. So if I go 1, 2, 3, 4 to reach the triple bond, or go from this end, 1, 2, 3, and I get to the triple bond. So this is the way I should number it. Alright. So we've figured out our substituents. We've determined our longest carbon chain that includes the triple bond. Step 4 through 6 is just using the rules that we've employed basically in other topics, namely alkanes with substituents. If you haven't watched that video, make sure you go back and take a look. Because in those videos, we talk about where we have to name the substituents alphabetically, and we also have to give numerical locations for them.
Alright. So 7 carbons is heptane. But remember, we change the ending from 'ane' to 'yne.' So here comes heptyne. The triple bond starts on carbon number 3, so 3-heptyne. Now we have to give the numerical locations of the substituents, and name them alphabetically. E comes before M. So we'd say that this would be, 5-ethyl, and then we have methyls on carbons 2 and 6, so 2,6-dimethyl. And then dash-three heptyne. So the name of this structure will be 5-ethyl-2,6-dimethyl-3-heptyne.
Give a systematic name for this molecule.
10-methyl-8-propyl-4-undecyne
10-methyl-8-propyl-4-undecane
8-sec-butyl-4-undecene
8-tert-butyl-4-undecene
Draw a structure for 4-ethyl-7-phenyl-2-heptyne.
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