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15.2: Naming Aldehydes and Ketones

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    Learning Objectives
    • Use the IUPAC system to name and draw aldehydes and ketones.

    Both common and International Union of Pure and Applied Chemistry (IUPAC) names are frequently used for aldehydes and ketones, with common names predominating for the lower homologs. The common names of aldehydes are taken from the names of the acids into which the aldehydes can be converted by oxidation.

    Chemical reaction diagram showing interconversion between formamide, formic acid, acetaldehyde, and acetic acid.

    The stems for the common names of the first four aldehydes are as follows:

    • 1 carbon atom: form-
    • 2 carbon atoms: acet-
    • 3 carbon atoms: propion-
    • 4 carbon atoms: butyr-

    Because the carbonyl group in a ketone must be attached to two carbon groups, the simplest ketone has three carbon atoms. It is widely known as acetone, a unique name unrelated to other common names for ketones.

    Molecular structure of acetone, showing the arrangement of carbon and oxygen atoms with the label "Acetone."

    Generally, the common names of ketones consist of the names of the groups attached to the carbonyl group, followed by the word ketone. (Note the similarity to the naming of ethers.) Another name for acetone, then, is dimethyl ketone. The ketone with four carbon atoms is ethyl methyl ketone.

    Chemical structure diagram of ethyl methyl ketone, featuring a central carbon atom double-bonded to oxygen.
    Example \(\PageIndex{1}\)

    Classify each compound as an aldehyde or a ketone. Give the common name for each ketone.

    1. Chemical structure of a compound showing a long carbon chain with a carbonyl group (C=O) attached.
    • Chemical structure diagram displaying a benzene ring connected to an alkyl chain, labeled "alkylbenzene."
    • Chemical structure diagram of a compound with carbon, oxygen, and hydrogen atoms.
    Solution
    1. This compound has the carbonyl group on an end carbon atom, so it is an aldehyde.
    2. This compound has the carbonyl group on an interior carbon atom, so it is a ketone. Both alkyl groups are propyl groups. The name is therefore dipropyl ketone.
    3. This compound has the carbonyl group between two alkyl groups, so it is a ketone. One alkyl group has three carbon atoms and is attached by the middle carbon atom; it is an isopropyl group. A group with one carbon atom is a methyl group. The name is therefore isopropyl methyl ketone.
    Exercise \(\PageIndex{1}\)

    Classify each compound as an aldehyde or a ketone. Give the common name for each ketone.

    1. Logo featuring the text "CHICKEN" above "OIL" with a stylized icon in between.
    • Two stylized figures with raised arms and a horizontal line connecting them below, resembling a minimalistic graphic design.
    • Chemical structure of a cyclic compound with a carbon ring and a branching functional group.

    Here are some simple IUPAC rules for naming aldehydes and ketones:

    Example \(\PageIndex{2}\)

    Give the IUPAC name for each compound.

    1. Two simple tools, a wrench and a screwdriver, are depicted above the text "DUCKPRICH."
    • Text illustration showing a line diagram labeled "P1" and "P2," with arrows indicating a connection between them.
    • Chemical structure of toluene, featuring a hexagonal benzene ring with a methyl group attached.
    Solution
    1. There are five carbon atoms in the LCC. The methyl group (CH3) is a substituent on the second carbon atom of the chain; the aldehyde carbon atom is always C1. The name is derived from pentane. Dropping the -e and adding the ending -al gives pentanal. The methyl group on the second carbon atom makes the name 2-methylpentanal.
    2. There are five carbon atoms in the LCC. The carbonyl carbon atom is C3, and there are methyl groups on C2 and C4. The IUPAC name is 2,4-dimethyl-3-pentanone.
    3. There are six carbon atoms in the ring. The compound is cyclohexanone. No number is needed to indicate the position of the carbonyl group because all six carbon atoms are equivalent.
    Exercise

    Give the IUPAC name for each compound.

    1. Chemical structure diagram featuring a carbon atom connected to various functional groups, including hydroxyl and aldehyde.
    • Fork and knife crossed over the words "Eat & Drink" in a minimalist design.
    • A simple flowchart element featuring a diamond shape with an arrow pointing to the right.
    Example \(\PageIndex{3}\)

    Draw the structure for each compound.

    1. 7-chlorooctanal
    2. 4-methyl–3-hexanone
    Solution
    1. The octan- part of the name tells us that the LCC has eight carbon atoms. There is a chlorine (Cl) atom on the seventh carbon atom; numbering from the carbonyl group and counting the carbonyl carbon atom as C1, we place the Cl atom on the seventh carbon atom.
      A stylized depiction of the phrase "Choose your adventure" in a playful font.
    • The hexan- part of the name tells us that the LCC has six carbon atoms. The 3 means that the carbonyl carbon atom is C3 in this chain, and the 4 tells us that there is a methyl (CH3) group at C4:
      Chemical structure of a compound featuring a carbon backbone with an ester functional group.
    Exercise

    Draw the structure for each compound.

    1. 5-bromo-3-iodoheptanal
    2. 5-bromo-4-ethyl-2-heptanone

    Concept Review Exercises

    Summary

    The common names of aldehydes are taken from the names of the corresponding carboxylic acids: formaldehyde, acetaldehyde, and so on. The common names of ketones, like those of ethers, consist of the names of the groups attached to the carbonyl group, followed by the word ketone. Stem names of aldehydes and ketones are derived from those of the parent alkanes, using an -al ending for an aldehydes and an -one ending for a ketone.

    1. The stem names of aldehydes and ketones are derived from those of the parent alkanes, defined by the longest continuous chain (LCC) of carbon atoms that contains the functional group.
    2. For an aldehyde, drop the -e from the alkane name and add the ending -al. Methanal is the IUPAC name for formaldehyde, and ethanal is the name for acetaldehyde.
    3. For a ketone, drop the -e from the alkane name and add the ending -one. Propanone is the IUPAC name for acetone, and butanone is the name for ethyl methyl ketone.
    4. To indicate the position of a substituent on an aldehyde, the carbonyl carbon atom is always considered to be C1; it is unnecessary to designate this group by number.
    5. To indicate the position of a substituent on a ketone, number the chain in the manner that gives the carbonyl carbon atom the lowest possible number. In cyclic ketones, it is understood that the carbonyl carbon atom is C1.

    6. Give the structure and IUPAC name for the compound that has the common name m-bromobenzaldehyde.

    7. Give the IUPAC name for glyceraldehyde, (HOCH2CHOHCHO). (Hint: as a substituent, the OH group is named hydroxy.)

    15.2: Naming Aldehydes and Ketones is shared under a CC BY-NC-SA 3.0 license and was authored, remixed, and/or curated by LibreTexts.