Naming Cyclic Alkanes - Online Tutor, Practice Problems & Exam Prep

Understanding the nomenclature of cycloalkanes is essential for students studying organic chemistry. Cycloalkanes are named similarly to their straight-chain counterparts, with the prefix "cyclo" indicating the cyclic nature of the molecule. The naming process involves identifying the parent chain as a cycloalkane and then determining the location of any substituents attached to the ring structure. Mastery of this naming convention allows for clear communication and identification of complex organic structures, which is a fundamental skill in the field of chemistry. This knowledge is foundational for progressing to more advanced topics in organic chemistry, such as the study of reactions and synthesis of cycloalkanes.

Rules for Naming Cyclic Alkanes

In this video we're going to talk about the way of naming cycloalkanes. Now we're going to say the name. The rules for naming cyclical canes or cycloalkanes are very similar to naming alkanes with substituents.

Here our naming convention will be looking at the location of each substituent, and because it's a cyclical cycloalkane, the parent chain is named as a cyclo parent chain.

So now that we know the basic naming structure, let's move on to the next video where we start naming different types of cycloalkane compounds.

Naming Cyclic Alkanes Example

Now here in this example question it says determine the systematic name of the following alkane. So to do that we're going to employ the following steps. So step one, it says assign name to the alkane ring. The ring here will serve as the parent according to its prefixes. Now you're going to add the prefix cyclo to the name of the alkane ring. Because it's no longer just an alkane, it's a cyclic alkane. So we're going to use cyclo.

Now Step 2. You're going to assign names to all the substituents on that ring. Step three, start numbering the chain from the closest substituent. Now, if only one substituent location is not necessary, if I tie between substituents, compare the the next closest substituent, it's still a tie number in alphabetical order. Now, from our previous videos, in terms of naming alkanes with substituents, we'd use steps 4:00 to 6:00. So repeating the same steps from that previous topic.

Remember this has to do with giving a location for the substituents, It has to do with naming substituents alphabetically. And then remember that we use commas to separate numbers from another and we use dashes to separate letters and numbers from one another. Now if we take a look here we have a one well, we have 123456 carbons long terms of our cyclic alkane. 6 carbons for an alkane is hexane, but it's not just hexane, it's a cyclic hexane, so we use the prefix cyclo.

So this is a cyclohexane ring and attached to it is a three carbon alkyl group. Since the bond is at one of the ends of this three carbonyl kill group, it represents propyl. Now here there's only this one substituent, so you don't need to give its numerical location because wherever it is located, that's where carbon number one will be in this case. So here we'd say that this is called propyl cyclohexane. This will be the name of this particular cyclical cane with its substituent.

Give a systematic name for the below compound.

• A. 1-sec-butyl-3-methylcyclopentane
• B. 1-methyl-3-sec-butylcyclopentane
• C. 1-butyl-3-methylcyclopentane
• D. 1-methyl-3-butylpentane

Here’s what students ask on this topic:

What is the naming of cycloalkanes?

The naming of cycloalkanes follows the rules set by the International Union of Pure and Applied Chemistry (IUPAC). Cycloalkanes are alkanes that form a closed ring structure. To name a cycloalkane:

1. Identify the number of carbon atoms in the ring. The root name of the cycloalkane is based on the number of carbons, just like in linear alkanes (e.g. "meth-" for one carbon, "eth-" for two, etc.).
2. Add the prefix "cyclo-" to the root name to indicate that the carbons form a ring. For example, a three-carbon ring is named cyclopropane.
3. If there are substituents (groups of atoms branching off the main ring), number the carbon atoms in the ring to give the lowest possible numbers to the substituents. Begin numbering at a substituent, and proceed around the ring in the direction that gives the lowest numbers to the substituents.
4. Name and number the substituents as prefixes to the cycloalkane name, and list them in alphabetical order. Use commas to separate numbers and hyphens to separate numbers from words.
5. If multiple substituents are identical, use prefixes such as di-, tri-, tetra-, etc., to indicate how many there are.

Is the ring always considered to be the chain when naming substituted cycloalkanes?

In the context of naming substituted cycloalkanes, the ring is not always considered the main chain. The main chain, or parent chain, is the longest continuous carbon chain in the molecule. For cycloalkanes, the ring is typically considered the main chain when it has more carbons than any alkyl substituent attached to it.

However, if there is an alkyl substituent that contains a longer carbon chain than the ring itself, then the alkyl substituent becomes the main chain, and the cycloalkane becomes a cycloalkyl substituent. In such cases, the compound is named as an alkane with a cycloalkyl group as a substituent.

When naming the compound, you would start with the name of the longest carbon chain as the base name, and then add the cycloalkyl group as a prefix, along with any other substituents, using appropriate locants to indicate their positions on the main chain. The entire name should reflect the structure in a way that is unambiguous and follows the rules set by the International Union of Pure and Applied Chemistry (IUPAC).

How to name cycloalkanes with branches?

When naming cycloalkanes with branches, follow these steps:

1. Identify the cycloalkane ring as the parent structure. The number of carbons in the ring determines the base name (e.g. cyclopropane, cyclobutane, cyclopentane, etc.).
2. Number the carbons in the ring starting from the point of attachment of the largest substituent (branch) as carbon-1. Proceed in a direction that gives the lowest possible numbers to the substituents.
3. If there are multiple substituents, continue numbering to give the lowest combination of numbers. If there's a tie, use alphabetical order to decide where to start numbering.
4. Name the substituents as you would for alkanes, but with a number indicating their position on the ring. Prefix the substituent names to the cycloalkane name.
5. If identical substituents are present, use prefixes such as di-, tri-, tetra-, etc., to indicate their quantity.
6. Assemble the name starting with the substituent prefixes in alphabetical order, followed by the cycloalkane name.

For example, a cyclohexane ring with a methyl group on the first carbon and an ethyl group on the second carbon is named 1-ethyl-2-methylcyclohexane.