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20.1 Naming Carboxylic Acids and Nitriles

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  • Page ID
    90981
  • Objectives

    After completing this section, you should be able to

    1. write the IUPAC name of a carboxylic acid, given its Kekulé, condensed or shorthand structure.
    2. draw the condensed or shorthand structure of a carboxylic acid, given its IUPAC name.
    3. draw the structure of the following carboxylic acids, given their trivial names: formic acid and acetic acid.
    4. provide an acceptable name for a nitrile of given structure.
    5. draw the condensed or shorthand structure of a nitrile, give either its trivial or IUPAC name.

    Key Terms

    Make certain that you can define, and use in context, the key terms below.

    • carboxylic acid
    • nitrile

    Study Notes

    You need not memorize all the trivial names listed in the table, just remember the two names identified in Objective 3, above.

    Carboxylic Acids, RCO2H

    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. These names were chosen by chemists to usually describe a source of where the compound is found. 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

    Example (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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    The acid with the carboxyl group attached directly to a benzene ring is called benzoic acid (C6H5COOH).

    benzoic acid.jpg

    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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    Naming Nitriles

    Name the parent alkane (include the carbon atom of the nitrile as part of the parent) followed with the word -nitrile. The carbon in the nitrile is given the #1 location position.  It is not necessary to include the location number in the name because it is assumed that the functional group will be on the end of the parent chain.

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    Cycloalkanes are followed by the word -carbonitrile. The substituent name is cyano.

    • 1-butanenitrile or 1-cyanopropane

    Try to name the following compounds using these conventions

      J

      J

    Try to draw structures for the following compounds

    • butanedinitrile
    • 2-methycyclohexanecarbonitrile 

     

    Some common names that you should know are...

      acetonitrile

      benzonitrile

    Try to draw a structure for the following compound

    • 2-methoxybenzonitrile

     

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