Nomenclature of Alkenes

As with any functional group there is a list of rules that must be followed for naming alkenes. 

Naming Alkenes

Concept: Rules for Naming Alkenes

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Video Transcript

Hey guys! In this new video, we're going to take a look at naming alkenes.
We're going to say naming an alkene is really similar to naming an alkane. There are a few differences here and there though. We're going to first find the longest carbon chain and now we're going to change the ending from -ane because it’s no longer an alkane to -ene because now it is an alkene. If there is a tie between longest chain, again choose the chain that gives more substituents. Here, number the chain from the end closest to the double bond and provide a number for its location. We'll see how that works. Substituents will be named alphabetically and a number of will company the location of their attachment as before. If there's more than one of that type, then we use numerical prefixes dimethyl or triethyl, tetra, and penta. Those rules are similar from before.
Here let's take a look at this ring. I’m going to give you guys a little bit of help in terms of it. When it comes to a ring, we want to start counting on the double bond. We're going to either count 1,2 or 1,2. Remember, you want to count in a way on the double bond that gets you to the substituent the fastest. The end of the name will be cyclo something because it's a ring. That methyl group is a substituent.
Knowing that, attempt to answer this question in naming of this compound. Come back and take a look at me answering the same exact question and see if your answer matches my answer. Good luck guys!

Example: Naming the following alkene compound. 

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Video Transcript

Alright guys. Let's take a look at that example that was left for us on the bottom of the page. Remember, if we have a ring, I told you that you have to count along the double bond. We want to count in a way to get to the substituent the fastest. Here this would be 1, 2, 3, 4, 5. We count them that way. This is a methyl group that is on carbon 3. This would be 3 methyl. In a ring, we don't have to state the location of the double bond. Wherever it is, that's going to be carbons 1 and 2. This would be 3-methyl cyclopentene. Cyclo because it's a ring. Pent because it's five carbons in the ring. Ene because it's an alkene.
We've seen this first example. Attempt to do the naming on the following page. Come back and take a look at the video of me explaining how to name the next practice example. Attempt it on your own guys. Compare your answer to mine and see if you got the correct answer.

Example: Naming the following alkene compound. 

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Video Transcript

Alright guys. We’re going to do the next practice question that dealt with naming alkenes. Here we have to name the following alkene compound. Remember, we want to look for the longest carbon chain. Here hopefully you were able to find the longest carbon chain. You could say that the longest carbon chain was this chain here. You could have also gone the opposite way where you did this and gave you the longest carbon chain. That would have also been an acceptable answer.
We'd say here now that this here, it would be our longest carbon chain. Our double bond is right here. You want to count from the end closest to the double bond. We can go 1, 2, 3, 4 and get to the carbon with the double bond or we can go 1, 2, 3 and get to the carbon with the double bond. We're going to go with the second way because we get there faster. We're going to say the double bond starts on carbon number 3. It's 3-heptene and then we have methyl groups on carbons 5 and 2 that didn't get numbered, so they're not part of the longest chain. They would be 2,5-dimethyl hyphen 3-heptene. That will be the name. Remember, the ending changes from -ane to -ene because now we're dealing with a double bond. The three just means carbon number three is the first carbon where the double bond starts.
Now that we've seen this, attempt to answer the next question. Again, this is similar to ones that we've done before with alkanes. Start with the end of the name. Draw that as the skeleton and then place everything where you need to. What does 2-heptene mean in terms of the structure of the compound? Knowing that is key to answering this question. So attempt this on your own and come back and take a look at my example.

Example: Determine the structure for the following alkene compound.

5-bromo-4,4-dimethyl-2-heptene

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Example: Determine the structure for the following alkene compound.

2, 5–octadiene 

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Example: Determine the structure for the following alkene compound.

Trans–3–hexene

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