Naming Alkanes with Substituents - Online Tutor, Practice Problems & Exam Prep

Rules for Naming Alkanes with Substituents Concept 1

So when it comes to naming Organic Compounds, the name consists of a parent chain, the name of substituents and their locations, and a substituent. Now, a substituent, we're going to say, is an alkyl group that branches off the parent chain. For this portion of naming, we're going to say the name format is the location of our substituent, and then ending with the parent name. Alright. So as we do more and more of these, the name format's going to become second nature to everyone. So, just pay attention, and take care because there are steps involved, a process. Remembering the process is the easiest way to name any organic compound you come face to face with.

Naming Alkanes with Substituents Example 1

Here it says, give the systematic name of the following alkane. Right. So to name this, we're going to have to follow the given steps. So, step 1, we find the longest carbon chain, which is the parent chain, and assign names according to the prefixes. Now, if there's a tie between the longest chain, choose the chain with more substituents. Now, when it comes to finding the longest carbon chain, you have to let go of the fact that we're reading from left to right. When it comes to looking at an organic molecule, you may look left to right, right to left, top to bottom, or bottom to top. You have to be able to look in all directions. So if we take a look here, what's the longest possible chain? Let's see. 1, 2, 3, 4. Okay. 1, 2, 3, 4, 5, 6, 7. 1, 2, 3, 4, 5, 6, 7. So it looks like there are 2 ways that give me 7. And regardless of which way you go, if we went this way, we'd have 2 substituents. This one branching off and this one branching off. If we went the other way, it'd be the same thing, where going this way, we'd have these 2 substituents. Alright. So our longest carbon chain is 7 carbons long.

Now, step 2, assign names to all substituents, and this is important. Step 3. Start numbering the chain from the closest substituent. If there's a tie between substituents, compare the next closest substituent. If still a tie, number in alphabetical order. Alright. So if we go down here, I've highlighted what we were just talking about. The longest carbon chain I decided to highlight it this way. This gives me a 7 carbon chain as the parent chain. And what's highlighted in orange are our substituents. So here we go 1-2-3, we get to this substituent, we go 1-2-3, we get to this substituent. It's tied. Counting the carbon 3 from either side gets us to a substituent. But if we identify these, this is 1 carbon, so this would be a methyl group. This is 2 carbons, so this is an ethyl group. We said, if still a tie, distance from the ends to the first substituent, number in alphabetical order. E comes before M, which means we're going to number it this way, 1-2-3, and then 4, 5, 6, 7.

Now, step 4, you're going to assign numbers, which gives us the location for each substituent. When more than 1 identical substituent, use the numerical prefixes of di for 2, tri for 3, and tetra for 4. Alright. So we have on carbon number 3, an ethyl. So this we're going to say, we're going to use 3-ethyl. Okay. Name substituents in alphabetical order. Prefixes do not count, use commas to separate numbers from numbers, and we're going to use dashes to separate letters from numbers. Letters are not separated from letters. So a lot is being said here, so let's work this out. We're going to name the substituents alphabetically, and we're going to give their number locations. So ethyl is on carbon number 3, so that's 3-ethyl. Methyl's on carbon number 5, so 5-methyl, and then we have a 7 carbon chain. 7 carbons is hept, and it's an alkane, so it's heptane. So this would be the name of this alkyl group, or this alkane molecule. 3-Ethyl-5-Methyl-heptane. This would be our final answer. Again, it gets a little bit jarring in terms of naming these types of molecules, but with enough practice it becomes second nature. So keep at it, and you'll get to master naming all these different types of organic compounds.

Provide a systematic name for the molecule. 



• A. 7-isopropyl-2,3-dimethyldecane
• B. 2,7,8-trimethyl-3-propylnonane
• C. 4-isopropyl-8,9-dimethyldecane
• D. 2,3,8-trimethyl-7-propylnonane

Draw a structure for 2,6-dimethyl-4-propylnonane. 

• A.
• B.
• C.
• D.

Draw a structure for 4-tert-butyl-3-isopropyl-2-methyloctane.

• A.
• B.
• C.
• D.