Naming Alkynes - Video Tutorials & Practice Problems
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concept
Rules for Naming Alkynes
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53s
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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 of -aim, coming from an alkane to -yene, because we're dealing with an alkyne. Now, a good thing here is that alkynes, because we have a triple bond, they 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 'yin'. So keep that in mind when we start naming different times of all kinds.
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example
Naming Alkynes Example
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4m
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Here 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 name according to the prefixes and modifier. Now, the parent chain should include a triple bond, and have greatest number of carbons or greater number of carbons. If a tie between along this chain, choose chain with more substituents. Step 2, you would assign name to all the substituents. Alright. So first, let's look at what the longest chain could possibly be here. So I need to make sure that the double bond, the the triple bond actually, 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 double next to the triple bond. 5, and then we could go 67. 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. Second carbon chain Alkyne. But look, how many substituents do we have now? 123. 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 substituent 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. K. Start numbering the chain from the end closest to the triple bond. Assign location to the 1st 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 changed the ending from aine to yin. So here comes have time. The triple bond starts on carbon number 3, so 3 have time. 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 26, so 2 comma 6. Since they're both the same substituent, we use the numerical, prefix, Dimethyl. Dimethyl. And then dash-three heptyne. So the name of this structure will be 5 Ethyl-twenty 6 Dimethyl-three Heptyne.