IUPAC Naming for Branched Alkanes

Leah here from leah4sci.com and in this video I will show you the IUPAC rules for naming branched alkanes. When naming branched alkanes, you get to add in the prefix portion to the naming puzzle. Remember a branch is simply another carbon group on the molecule that doesn't flow with your straight chain. Here are a few rules that I like to use when naming branched alkanes. First identify your parent chain. This is the longest carbon chain that you can trace without lifting your highlighter. Next you want to number your chain so that your substituent gets the lowest number. Next you want to name your parent and substituents using the format introduced in the first video but adding the following details. You have to include a number for each substituent telling where it shows up on the parent chain. Use the prefix that identifies the number of carbons and then add the letters YL to show that it's a substituent. And last but not least, tell how many of each substituent you have. If you have a single substituent, you don't need a number because it is understood to be 1. If you have more than 1, include the prefix di for 2, tri 3, tetra 4 and penta 5. Let's start with this simple example. I like to mark up my chain as I put the puzzle pieces together because this way I know what I named and what I have yet to name. We highlight the longest carbon chain which is our parent chain and number from the side that gives me the lowest number for my substituent. I have the option of naming from the right giving me 1, 2 and a substituent on 3 or naming from the left which gives me 1, 2 and a substituent on 2. Since 2 is lower than 3, I can name the substituent on the left. I can also name I have to number from the left. This gives me a parent chain of four carbons and the first name of Bute. Only single bonds gives me a last name of Ain. For my substituent, I have one carbon on carbon number two. I use the number two since it's the second carbon on the parent chain, Mef to show that it's a single carbon and Yl to show that it's a substituent. Putting the name together, this is my prefix, I'm going to name it as a substituent. This is my first, ane is my last name giving this molecule the name of 2-methylbutane. Now let's try adding a second group to this molecule. We'll approach it the same way. Highlight the parent chain and then number so that you have the lowest number for the substituents. One more time, a number from the left for a total of 4 carbons. 4 carbons gives me a first name of bute. Single bonds gives me a last name of ane and now I have two substituents both coming off of carbon 2. Since the substituents are the same, they're both methyls, I write 2,2-dimethyl. The reason I include two number 2s is that both substituents are a number 2 and the di tells me that there's two of the methyl group. You have to include both the numbers and the di. This way I know how many I have and exactly where each one shows up. Notice the way I structured the name of the substituent. You use a comma when you have a number followed by another number and a dash when you have a number and a letter or a letter and a number. In this case, I have 2,2 and then the second 2 gets a dash to dimethyl. Putting the name together, I have 2,2-dimethylbutane. and notice there is no space between the substituents and the parent chain but rather it's all one word. Now let's look at an example that has two different substituents. I start by highlighting my parent chain and then numbering from the side that gives me the lowest number for the first substituent I come across. This means if I start from the right, I get 1, 2, 3 for my first group or if I start from the left, I get 1, 2. Since 2 is lower than 3, I start counting from the left for a total of 7 giving me a first name of hept. Since I have only single bonds, I have ane and that's my parent name. Now let's look at the substituents. On carbon number 2, I have a single carbon substituent. This is a 2-methyl and on carbon number 5, I have a 2-carbon substituent which gives me the name 5-. With more than one substituent, you order them in alphabetical order so we'll compare M to E. Since E comes before M, I get a final name of 5-ethyl-2-methyl-heptane. And now for a tricky example. At first glance, it appears that my parent chain only has 5 carbons. However, don't go by what appears to be the longest chain. Remember that carbon to carbon bonds can rotate and so your chain can actually be slightly twisted. In fact, the longest carbon chain actually extends downwards for a total of 6 carbons. I've adapted the junction rule from physics to help you easily identify your longest carbon chain. Instead of counting 1, 2, 3, going this way, going that way, going that way, this can potentially take a long time. Instead identify your junction or the one point that has multiple chains coming out of it and then simply identify your longest pieces. Notice that to the right I have 2, to the left I have 2 but going down I have 3. This tells me that my parent chain has to include the branch going down. And since I have two to the right and to the left, I can arbitrarily choose one for the longest carbon chain. Now that I've identified the longest carbon chain, I continue with the standard naming. Starting from the left, I have a total of six carbons for a first name of hex, single bonds gives me ane and a two carbon substituent of carbon three gives me three ethyl. Putting the name together, I have three ethyl hexane. Let's do one last tricky example by naming this molecule. Don't be fooled by the obvious which appears to be a carbon chain of 6 when in fact I have a much longer carbon chain. Applying the junction rule, I have a branch here, here, here and here. But let's not get carried away, let's only take the branches that are not obvious at first glance to be our longest carbon chains. And so the one tricky branch to look at is right here. To I have 2 carbons, counting upwards I have 3 carbons and counting to the left I also have 3 carbons. I verify this with a highlighter trick where I start highlighting at one end and make sure I can get all the way to the other end without having to lift my highlighter. And so we get a total of 1, 2, 3, 4, 5, 6, 7 carbons in my longest carbon chain. I have the option of numbering from the left which gives me my first substituent at 2. We're numbering from the top which also gives me the first substituent at 2. So I have to number it one more step and see which one has more substituents for lower numbers. From the left, I have another substituent at 3, from the top I don't have a substituent at 3 and so I have to count from the left. This is where the puzzle idea comes in handy. If you try to name this as you see it, you're likely to make a mistake but if you mark off each piece individually. By naming that aspect of the puzzle, the entire thing will come together nicely. I have seven carbons giving me a first name of hept, I have only single bonds giving me ane and now let's look at substituents. I have a methyl group on carbon 2, 3 and 6 and so I named this 2,3,6-trimethyl. I also have a 2-carbon substituent on number 4. which gives me 4-ethyl and that's it. Every piece of my molecule is marked and numbered, every puzzle piece is named and now I put the puzzle together. Your substituents are named in alphabetical order but we don't look at the prefix tri. Tri is just an identifier but the actual letter to look at is M compared to E. Since E comes before M, you get a final name of 4-ethyl-236-trimethylheptane. In the next video, we'll look at how to name alkanes that have branches on their branches. Are you struggling with organic chemistry? Are you looking for information to guide you through the course and help you succeed? If so, download my e-book, 10 Secrets to Acing Organic Chemistry, using the link below, or visit leah4sci.com slash orgo secrets. That's O-R-G-O secrets. For information regarding online tutoring, visit leah4sci.com slash orgotutor. That's O-R-G-O, tutor. If you enjoyed this video, please give it a thumbs up and even share it with a friend or two. If you have any questions regarding this video, leave a comment below or contact me through my Facebook page at facebook.com forward slash leah4sci. There will be many related videos posted over the course of the semester, so go ahead and click the subscribe button to ensure that you don't miss out.

First identify your parent chain. This is the longest carbon chain that you can trace without lifting your highlighter. Next you want to number your chain so that your substituent gets the lowest number.

Next you want to name your parent and substituents using the format introduced in the first video but adding the following details. You have to include a number for each substituent telling where it shows up on the parent chain. Use the prefix that identifies the number of carbons and then add the letters YL to show that it's a substituent.

And last but not least, tell how many of each substituent you have. If you have a single substituent, you don't need a number because it is understood to be 1. If you have more than 1, include the prefix di for 2, tri 3, tetra 4 and penta 5. Let's start with this simple example. I like to mark up my chain as I put the puzzle pieces together because this way I know what I named and what I have yet to name.

We highlight the longest carbon chain which is our parent chain and number from the side that gives me the lowest number for my substituent. I have the option of naming from the right giving me 1, 2 and a substituent on 3 or naming from the left which gives me 1, 2 and a substituent on 2. Since 2 is lower than 3, I can name the substituent on the left. I can also name I have to number from the left. This gives me a parent chain of four carbons and the first name of Bute. Only single bonds gives me a last name of Ain.

For my substituent, I have one carbon on carbon number two. I use the number two since it's the second carbon on the parent chain, Mef to show that it's a single carbon and Yl to show that it's a substituent. Putting the name together, this is my prefix, I'm going to name it as a substituent. This is my first, ane is my last name giving this molecule the name of 2-methylbutane.

Now let's try adding a second group to this molecule. We'll approach it the same way. Highlight the parent chain and then number so that you have the lowest number for the substituents.

One more time, a number from the left for a total of 4 carbons. 4 carbons gives me a first name of bute. Single bonds gives me a last name of ane and now I have two substituents both coming off of carbon 2. Since the substituents are the same, they're both methyls, I write 2,2-dimethyl. The reason I include two number 2s is that both substituents are a number 2 and the di tells me that there's two of the methyl group. You have to include both the numbers and the di.

This way I know how many I have and exactly where each one shows up. Notice the way I structured the name of the substituent. You use a comma when you have a number followed by another number and a dash when you have a number and a letter or a letter and a number. In this case, I have 2,2 and then the second 2 gets a dash to dimethyl. Putting the name together, I have 2,2-dimethylbutane.

and notice there is no space between the substituents and the parent chain but rather it's all one word. Now let's look at an example that has two different substituents. I start by highlighting my parent chain and then numbering from the side that gives me the lowest number for the first substituent I come across. This means if I start from the right, I get 1, 2, 3 for my first group or if I start from the left, I get 1, 2. Since 2 is lower than 3, I start counting from the left for a total of 7 giving me a first name of hept. Since I have only single bonds, I have ane and that's my parent name.

Now let's look at the substituents. On carbon number 2, I have a single carbon substituent. This is a 2-methyl and on carbon number 5, I have a 2-carbon substituent which gives me the name 5-. With more than one substituent, you order them in alphabetical order so we'll compare M to E.

Since E comes before M, I get a final name of 5-ethyl-2-methyl-heptane. And now for a tricky example. At first glance, it appears that my parent chain only has 5 carbons.

However, don't go by what appears to be the longest chain. Remember that carbon to carbon bonds can rotate and so your chain can actually be slightly twisted. In fact, the longest carbon chain actually extends downwards for a total of 6 carbons. I've adapted the junction rule from physics to help you easily identify your longest carbon chain. Instead of counting 1, 2, 3, going this way, going that way, going that way, this can potentially take a long time.

Instead identify your junction or the one point that has multiple chains coming out of it and then simply identify your longest pieces. Notice that to the right I have 2, to the left I have 2 but going down I have 3. This tells me that my parent chain has to include the branch going down. And since I have two to the right and to the left, I can arbitrarily choose one for the longest carbon chain.

Now that I've identified the longest carbon chain, I continue with the standard naming. Starting from the left, I have a total of six carbons for a first name of hex, single bonds gives me ane and a two carbon substituent of carbon three gives me three ethyl. Putting the name together, I have three ethyl hexane.

Let's do one last tricky example by naming this molecule. Don't be fooled by the obvious which appears to be a carbon chain of 6 when in fact I have a much longer carbon chain. Applying the junction rule, I have a branch here, here, here and here. But let's not get carried away, let's only take the branches that are not obvious at first glance to be our longest carbon chains.

And so the one tricky branch to look at is right here. To I have 2 carbons, counting upwards I have 3 carbons and counting to the left I also have 3 carbons. I verify this with a highlighter trick where I start highlighting at one end and make sure I can get all the way to the other end without having to lift my highlighter. And so we get a total of 1, 2, 3, 4, 5, 6, 7 carbons in my longest carbon chain. I have the option of numbering from the left which gives me my first substituent at 2. We're numbering from the top which also gives me the first substituent at 2. So I have to number it one more step and see which one has more substituents for lower numbers.

From the left, I have another substituent at 3, from the top I don't have a substituent at 3 and so I have to count from the left. This is where the puzzle idea comes in handy. If you try to name this as you see it, you're likely to make a mistake but if you mark off each piece individually.

By naming that aspect of the puzzle, the entire thing will come together nicely. I have seven carbons giving me a first name of hept, I have only single bonds giving me ane and now let's look at substituents. I have a methyl group on carbon 2, 3 and 6 and so I named this 2,3,6-trimethyl.

I also have a 2-carbon substituent on number 4. which gives me 4-ethyl and that's it. Every piece of my molecule is marked and numbered, every puzzle piece is named and now I put the puzzle together. Your substituents are named in alphabetical order but we don't look at the prefix tri. Tri is just an identifier but the actual letter to look at is M compared to E.

Since E comes before M, you get a final name of 4-ethyl-236-trimethylheptane. In the next video, we'll look at how to name alkanes that have branches on their branches. Are you struggling with organic chemistry?

Are you looking for information to guide you through the course and help you succeed? If so, download my e-book, 10 Secrets to Acing Organic Chemistry, using the link below, or visit leah4sci.com slash orgo secrets. That's O-R-G-O secrets.

For information regarding online tutoring, visit leah4sci.com slash orgotutor. That's O-R-G-O, tutor. If you enjoyed this video, please give it a thumbs up and even share it with a friend or two.

If you have any questions regarding this video, leave a comment below or contact me through my Facebook page at facebook.com forward slash leah4sci. There will be many related videos posted over the course of the semester, so go ahead and click the subscribe button to ensure that you don't miss out.

Transcript for:IUPAC Naming for Branched Alkanes

Transcript for:
IUPAC Naming for Branched Alkanes