Naming Ketones: Videos & Practice Problems

Ketones are organic compounds characterized by a carbonyl group ($C=O$) attached to two carbon atoms. When naming ketones, the suffix '-one' is used in place of '-e' in the corresponding alkane name to indicate the presence of the carbonyl group. It's crucial to specify the location of the carbonyl group and any substituents on the parent chain to accurately name the ketone. This systematic approach to nomenclature ensures that the structure of the ketone is clearly communicated, reflecting the importance of precision in organic chemistry.

Rules for Naming Ketones

Ketones are organic compounds characterized by a carbonyl group (C=O) bonded to two carbon atoms. The naming conventions for ketones closely resemble those used for alcohols, with a key distinction in the suffix. Specifically, the 'e' at the end of the alkane name is replaced with 'one' to indicate the presence of a ketone. For example, the ketone derived from pentane is named pentanone.

When naming ketones, it is essential to identify the longest carbon chain that includes the carbonyl group, as this will serve as the parent chain. The position of the carbonyl group must be indicated by a number, which corresponds to the carbon atom in the chain where the carbonyl is located. Additionally, if there are any substituents attached to the carbon chain, their positions must also be specified. This systematic approach ensures clarity in the naming of ketones, allowing for accurate communication of their structure.

Naming Ketones Example

To determine the formal name of a ketone, follow a systematic approach that involves identifying the longest carbon chain, naming substituents, and assigning appropriate locational numbers. The carbonyl group, represented by the structure $C^1=O^1$, must be included in the parent chain, which should have the maximum number of carbon atoms. In cases where there is a tie in chain length, the chain with more substituents should be selected.

For example, consider a structure where the longest carbon chain consists of eight carbon atoms. The substituent branching off this main chain is identified as a methyl group. The next step involves numbering the carbon chain starting from the end closest to the carbonyl carbon. This results in a numbering sequence of 1 through 8, with the carbonyl carbon located at carbon number 2.

When naming the substituents, it is essential to provide their numerical locations. In this case, the methyl substituent is located on carbon 5, leading to the designation of 5-methyl. Since the parent chain contains eight carbons, the base name is derived from octane, and the presence of the carbonyl group modifies it to octanone. The final name combines these elements, resulting in 5-methyl-2-octanone.

In summary, the systematic naming of ketones involves identifying the longest carbon chain, numbering it appropriately, and naming substituents with their respective locations, ultimately leading to a comprehensive name that reflects the structure of the compound.

Provide the systematic name for the following ketone.

• A. 4,4-dichloro-2-hexanone
• B. 3,3-dichloro-2-hexanone
• C. 4,4-dichloro-5-hexanone
• D. 3,3-dichloro-5-hexanone

Answer: (B)

Which of the following compounds represent $2,4-dimethyl-3-pentanone$?

• A.
• B.
• C.
• D.

Answer: (D)

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How do you name a ketone?

Naming a ketone in organic chemistry follows the International Union of Pure and Applied Chemistry (IUPAC) nomenclature rules. Here's a simple guide to name a ketone:

1. Identify the longest carbon chain that includes the carbonyl group (C=O). This chain determines the base name of the ketone.
2. Number the carbon chain starting from the end nearest to the carbonyl group, so that the carbonyl carbon gets the lowest possible number.
3. The carbonyl group in a ketone is always located at a carbon atom that's within the chain, not at the end, so it will have a number associated with its position.
4. The suffix for ketones is "-one," which replaces the "-e" from the corresponding alkane name of the longest chain.
5. Combine the position number of the carbonyl group with the base name, placing the number in front of the base name. For example, if the carbonyl is on the second carbon of a four-carbon chain, the base name is "butanone" (butane + one), and it is written as "2-butanone."
6. If there are other substituents or groups attached to the main chain, name them as prefixes, and give them location numbers as well.

How do you name a ketone as a substituent?

When naming a ketone as a substituent in organic chemistry, you use the prefix "oxo-" to indicate the presence of a ketone group attached to the longest carbon chain, which is considered the parent compound. The ketone group is not included in the parent chain but is treated as a substituent.

To properly name it, you must identify the carbon to which the ketone is attached. You number the parent chain in such a way that the substituents get the lowest possible numbers. The position of the ketone group is indicated by a number corresponding to the carbon to which it is attached.

For example, if a ketone group is attached to the second carbon of a butane molecule, it would be named as "2-oxobutane." Here, "butane" represents the four-carbon parent chain, "oxo-" indicates the presence of a ketone group, and "2-" tells you that the ketone is attached to the second carbon atom. Remember that when the ketone is the highest priority functional group, it is named as part of the parent chain using the suffix "-one," but as a substituent, "oxo-" is the correct prefix.

How do you name a ketone using IUPAC?

To name a ketone using the International Union of Pure and Applied Chemistry (IUPAC) nomenclature, you follow these steps:

1. Identify the longest carbon chain that includes the carbonyl group (C=O). The carbonyl group is the functional group of ketones.
2. Number the carbon chain starting from the end nearest to the carbonyl group, so that the carbonyl carbon gets the lowest possible number.
3. Write the name of the alkane that corresponds to the longest chain, but replace the -e ending with -one to indicate the presence of a ketone. For example, if the longest chain has five carbons, the alkane would be pentane, and the ketone would be pentanone.
4. Indicate the position of the carbonyl group by placing the number of the carbonyl carbon in front of the ketone name. For example, if the carbonyl group is on the second carbon, the compound is named 2-pentanone.
5. If there are any substituents (additional groups or atoms attached to the main chain), name them as prefixes, and give their position numbers. List substituents in alphabetical order before the ketone name.

Example: 4-ethyl-2-pentanone indicates a ketone with an ethyl group on the fourth carbon and a carbonyl group on the second carbon.