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Chemistry LibreTexts

3.13: Carboxylic Acids

  • Page ID
    107508
  • learning objectives

    • name carboxylic acids using IUPAC (systematic) and selected common name nomenclature
    • draw the structure of carboxylic acids from IUPAC (systematic) and selected common names

    The IUPAC system of nomenclature assigns a characteristic suffix to these classes. The –e ending is removed from the name of the parent chain and is replaced -anoic acid. Since a carboxylic acid group must always lie at the end of a carbon chain, it is always is given the #1 location position in numbering and it is not necessary to include it in the name. Many carboxylic acids are called by the common names that were chosen by chemists to usually describe the origin of the compound. In common names of aldehydes, carbon atoms near the carboxyl group are often designated by Greek letters. The atom adjacent to the carbonyl function is alpha, the next removed is beta and so on.

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    Formula

    Common Name

    Source

    IUPAC Name

    Melting Point

    Boiling Point

    HCO2H formic acid ants (L. formica) methanoic acid 8.4 ºC 101 ºC
    CH3CO2H acetic acid vinegar (L. acetum) ethanoic acid 16.6 ºC 118 ºC
    CH3CH2CO2H propionic acid milk (Gk. protus prion) propanoic acid -20.8 ºC 141 ºC
    CH3(CH2)2CO2H butyric acid butter (L. butyrum) butanoic acid -5.5 ºC 164 ºC
    CH3(CH2)3CO2H valeric acid valerian root pentanoic acid -34.5 ºC 186 ºC
    CH3(CH2)4CO2H caproic acid goats (L. caper) hexanoic acid -4.0 ºC 205 ºC
    CH3(CH2)5CO2H enanthic acid vines (Gk. oenanthe) heptanoic acid -7.5 ºC 223 ºC
    CH3(CH2)6CO2H caprylic acid goats (L. caper) octanoic acid 16.3 ºC 239 ºC
    CH3(CH2)7CO2H pelargonic acid pelargonium (an herb) nonanoic acid 12.0 ºC 253 ºC
    CH3(CH2)8CO2H capric acid goats (L. caper) decanoic acid 31.0 ºC 219 ºC

    Examples (Common Names Are in Red)

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    Naming carboxyl groups added to a ring

    When a carboxyl group is added to a ring the suffix -carboxylic acid is added to the name of the cyclic compound. The ring carbon attached to the carboxyl group is given the #1 location number.

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    Naming carboxylates

    Salts of carboxylic acids are named by writing the name of the cation followed by the name of the acid with the –ic acid ending replaced by an –ate ending. This is true for both the IUPAC and Common nomenclature systems.

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    Naming carboxylic acids which contain other functional groups

    Carboxylic acids are given the highest nomenclature priority by the IUPAC system. This means that the carboxyl group is given the lowest possible location number and the appropriate nomenclature suffix is included. In the case of molecules containing carboxylic acid and alcohol functional groups the OH is named as a hydroxyl substituent. However, the l in hydroxyl is generally removed.

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    In the case of molecules containing a carboxylic acid and aldehydes and/or ketones functional groups the carbonyl is named as a "Oxo" substituent.

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    In the case of molecules containing a carboxylic acid an amine functional group the amine is named as an "amino" substituent.

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    When carboxylic acids are included with an alkene the following order is followed:

    (Location number of the alkene)-(Prefix name for the longest carbon chain minus the -ane ending)-(an –enoic acid ending to indicate the presence of an alkene and carboxylic acid)

    Remember that the carboxylic acid has priority so it should get the lowest possible location number. Also, remember that cis/tran or E/Z nomenclature for the alkene needs to be included if necessary.

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    Naming dicarboxylic acids

    For dicarboxylic acids the location numbers for both carboxyl groups are omitted because both functional groups are expected to occupy the ends of the parent chain. The ending –dioic acid is added to the end of the parent chain.

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    Common Names for selected dicarboxylic acids

    The following common names for these selected dicarboxylic acids are important to memorize; they are prevalent in biochemistry or industrial applications.

    dicarboxylic acids.png

    The saying, "Oh my, such good apple pie!", can help us remember these common names by correlating the first letters of each word with the common names:

    oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, and phthalic.

    Exercise

    1. Draw the bond-line structure and write the condensed structural formula for each compound.

    a) octanoic acid

    b) 4-hydroxypentanoic acid

    c) cis-4-hexenoioc acid or cis-hex-4-enoic acid

    d) (E)-5-bromo-3-heptenoic acid or (E)-5-bromohept-3-enoic acid.

    e) 2-aminopropanoic acid

    2. Give the IUPAC name and condensed structural formula for each compound.

    ch3 sect 13 exer 2 cpds.png

    Answer

    1.

    ch3 sect 13 exer 1 solutions.png

    2.

    ch3 sect 13 exer 2 solution.png

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