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

Native organic compounds are named using a systematic approach that includes identifying the parent chain, substituents, and their locations. A substituent, typically an alkyl group, branches off the parent chain. The naming format follows the structure: location of the substituent followed by the parent name. Mastering this process simplifies the naming of organic compounds, which is essential for understanding concepts like functional groups, isomers, and reaction mechanisms in organic chemistry.

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.

Here’s what students ask on this topic:

What is the process for naming alkanes with substituents?

Naming alkanes with substituents involves several steps. First, identify the longest continuous carbon chain, which will serve as the parent chain. Next, identify and name the substituents, which are alkyl groups branching off the parent chain. Number the carbon atoms in the parent chain starting from the end nearest a substituent to give the substituents the lowest possible numbers. Finally, write the name by listing the substituents in alphabetical order, each preceded by its location number, followed by the parent chain name. For example, 2-methylpentane indicates a methyl group on the second carbon of a five-carbon chain.

How do you determine the parent chain in an alkane?

The parent chain in an alkane is the longest continuous chain of carbon atoms. If there are multiple chains of the same length, choose the one with the most substituents. This ensures that the naming process reflects the most complex structure. For example, in a molecule with chains of six and seven carbons, the seven-carbon chain is the parent chain. If two chains of equal length exist, select the one with the greatest number of substituents.

What are common mistakes to avoid when naming alkanes with substituents?

Common mistakes include not identifying the longest parent chain, incorrectly numbering the carbon atoms, and not listing substituents in alphabetical order. Always ensure the parent chain is the longest possible, number the chain to give substituents the lowest possible numbers, and list substituents alphabetically regardless of their position. For example, in 3-ethyl-2-methylhexane, 'ethyl' comes before 'methyl' alphabetically, even though 'methyl' is on the second carbon.

How do you name a compound with multiple substituents?

When naming a compound with multiple substituents, first identify the parent chain and number it to give the substituents the lowest possible numbers. List each substituent with its corresponding number, and if there are multiple identical substituents, use prefixes like di-, tri-, and tetra-. For example, 2,3-dimethylbutane indicates two methyl groups on the second and third carbons of a four-carbon chain. Always list substituents in alphabetical order, ignoring prefixes when alphabetizing.

What is the significance of the IUPAC naming system in organic chemistry?

The IUPAC naming system provides a standardized method for naming organic compounds, ensuring clear and consistent communication among chemists worldwide. It helps avoid confusion by providing a unique name for each compound based on its structure. This system is essential for understanding and discussing chemical reactions, mechanisms, and properties. For example, the name 2-methylpropane immediately conveys the structure of the compound, allowing chemists to understand its reactivity and behavior in different contexts.