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7.4: Aldehydes

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    1. The suffix -al is appended to the name of the hydrocarbon corresponding to the longest carbon chain that includes the aldehyde carbon. Remember that alkane \(+\) -al becomes alkanal with the e omitted, and because the al function is necessarily at \(C1\), the -1- is redundant and is omitted:

    Left: C H 3 C H 2 C H 2 C H 2 C H 2 C H O. Labeled hexanal. Right: H C double bond C C H 2 C H 2 C H C H 2 C H O. C H 3 substituent on carbon 3. Labeled 3-methyl-6-heptynal.

    Dialdehydes are named as -dials. Thus \(OHCCH_2CH_2CH_2CH_2CHO\) is hexanedial.

    2. The simplest aldehyde is methanal, \(HCHO\), which is familiarly known as formaldehyde. However, when aldehydes are named as derivatives of methanal, they usually are called carbaldehydes, and the suffix "carbaldehyde" refers to the \(-CHO\) group. This system is used where the hydrocarbon group is not a chain, but a ring, and the \(CHO\) group can be thought of as a one-carbon chain:

    Left: cyclohexane with C H O substituent. Labeled cyclohexanecarbaldehyde. Right: benzene ring with C H O substituents on carbons 1 and 4. Labeled 1,4-benzenedicarbaldehyde.

    3. When the \(-CHO\) group is a substituent on the parent chain or ring and it ranks below another functional group, it properly is designated by the prefix methanoyl. However, the prefix formyl also is used:

    C H 3 C H 2 C H C H 2 C O 2 H. C H O substituent on carbon 3. Labeled 3-methanoylpentanoic acid (3-formylpentanoic acid).

    (The naming of acids will be discussed more in detail in Section 7-6.)

    4. Trivial names are used for many simple aldehydes, some of which are shown below in parentheses:

    From left to right: C H 3 C H O. Labeled ethanal (acetaldehyde). Benzene ring with C H O substituent. Labeled benzenecarbaldehyde (benzaldehyde). Benzene ring with C H O substituent on carbon 1 and O C H 3 substituent on carbon 4. Labeled 4-methoxy-benzenecarbaldehyde (anisaldehyde). O H C single bond C H O. Labeled ethanedial (gyloxal).

    Contributors and Attributions

    John D. Robert and Marjorie C. Caserio (1977) Basic Principles of Organic Chemistry, second edition. W. A. Benjamin, Inc. , Menlo Park, CA. ISBN 0-8053-8329-8. This content is copyrighted under the following conditions, "You are granted permission for individual, educational, research and non-commercial reproduction, distribution, display and performance of this work in any format."

    This page titled 7.4: Aldehydes is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by John D. Roberts and Marjorie C. Caserio.

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