Naming Alkenes - Video Tutorials & Practice Problems
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concept
Rules for Naming Alkenes
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Now, before we get into naming alkenes, recall that alkenes possess a carbon, carbon double bond. And the set of rules for naming our Keynes is unique here. We're going to say that the modification is we're gonna modify the ending from A to E. So we're thinking of an alkene, but because there's the presence of a double bond, it becomes an alkene. This naming convention will have things called cis and trans which we'll go into. We still have to give the location of our substituents. We have to give the location of our parent in terms of the double bond. And then we have our modifier where we change the ending from A to E. Now, here we call that geometric isomers have a different spatial orientation around a double bond. And remember that rotation is not possible around a double bond, which is a pi bond. Now, we need to indicate which side of the double bond, both groups um where, where both or each group lies. And we do this by saying cis or trans. Now this only applies when there are two groups around a pi bond. So if we take a look here we have our two double bodied carbons here and we have our two groups which happen to be these metal groups, we create a border, this border dissects right through the double bonded carbons. And you're either here on the bottom side or you're here on the top side. So you're different sides of the, of the pie bond. Both methyl groups happen to be on the same side. When they're on the same side. we say that this is cis. Now here, if we take a look at this alkene, this is a geometric isomer with the same molecular formula, same connections, just a slight difference in spatial orientation. Again, here are two double bonded carbons. We create a border by cutting straight through them. Now we have one metal group up here and one metal group down here, they're on different sides of this border that we've created. So if they're on different sides, that means that they are trans. So here we have a cis alkene on the left and a trans alkene on the right. Now, if we're dealing with a cyclic alkene, we're gonna say there are no cis or trans within the rank. So we don't have to worry about this type of notation. So again, for us to be cis or trans, we need to have two groups that are connected to our double bonded carbons. If they're on the same side, it's cis, if they're on opposite sides, it's trans
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example
Naming Alkenes Example
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Here, it says, determine the systematic name of the following a key. So to name this alkene, we're gonna follow the given steps here. It says, find the longest carbon chain which represents our parent chain and assign a name according to the prefix and the modifier, the parent chain should include a double bond and have greater number of carbons. Now, if it's cyclic, we add the prefix of cyclo to the name of the alkene chain. If a tie between longest chains choose chain with more substituents. So if we take a look here, what's our longest chain? Our longest chain appears to be this year, this carbon up here, which is a methyl is our substituent. So step two says, assigned name to all substituents. So this would be methyl, start numbering the change from the end closest to the double bond. So the double bond is here on the left. So we'd start numbering on this side. 12345 and six, assigned location to the first double bonded carbon. If dan in a ring, no location is not necessary. Repeat from um previous naming topics. So go back and take a look at my videos on naming our cans of substituents because it talks about how we give the numerical location for each of the substituents, how we name them alphabetically. And here we have step seven where we add sis or trans designation to the front of the name, if applicable. All right. So first, let's just name this before we worry about sis and train. We're gonna say here substituent is methyl. It's on carbon number four. So it'd be four methyl. We then have to talk about the first double bonded carbon. The double bond starts on carbon number two. So we'd say the location is two. It's a six carbon chain which is hexane as an alkane. But here it's an alkene. So we changed the a ending to E. So this would be two hexane. Now, we said that if we have two groups attached to our pi bond, then we use CIS and trans. So here is a group attached to our double bonded carbon which contains the pi bond. And here is another group attached. So we do have two groups attached to our pie bonds in terms of those two Al King carbons. Remember we create a border here between the double bonded carbons and we can see that the two groups that is um basically put in within those blue boxes, they're on different sides of this border because they're on different sides of this border. That means that they are trans to one another. So we put trans at the beginning of the name. So the name of this particular alke would be trans, four methyl, two hexen.
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Problem
Problem
Provide systematic name for given alkene.
A
trans-2,7-dimethyl-3-octene
B
2,7-dimethyl-3-octane
C
trans-2,7-dimethyl-5-octene
D
2,7-dimethyl-5-octane
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Problem
Problem
Provide systematic name for given alkene.
A
3-ethyl-5-hexene
B
4-isopropyl-1-hexene
C
4-ethyl-1-hexene
D
4-isopropyl-2-hexene
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Problem
Problem
Draw a structure for cis-5-methyl-2-hexene.
A
B
C
D
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Problem
Problem
Determine the structure of the following alkene: 3-isopropylcyclohexene.