Basic Organic Nomenclature

An Introduction

Dave Woodcock,
Associate Professor Emeritus UBC (Okanagan)
©1996,2000, 2008

6. Aromatic Compouds

II Disubstituted Benzenes

Index


  1. There are only 3 isomers for any particular disubstituted benzene because of the symmetry of the planar ring. To identify these, the IUPAC system prefers the use of numbers: 1,2; 1,3; 1,4.
    However, there is in very common use another system which uses the prefixes:
    ortho-, or o- for the 1,2 isomer;
    meta-, or m- for the 1,3 isomer;
    para-, or p- for the 1,4 isomer;

    Examples:


    1,2-dichlorobenzene, o-dichlorobenzene


    1,3-dibromobenzene, m-dibromobenzene


    1-bromo-4-chlorobenzene, p-bromochlorobenzene


    1,3-dinitrobenzene, m-dinitrobenzene

  2. Unique common names are used for some disubstituted benzenes...they need to be learned!


    o-xylene

    Also: meta- and para-xylene


    m-cymene

    Also: ortho- and para-cymene


    p-toluidine

    Also: ortho- and meta-toluidine


    p-cresol

    Also: ortho- and meta-cresol


    phthalic acid

    The 1,3 derivative is isophthalic acid, and the 1,4 derivative is terephthalic acid


    anthranilic acid

    Only used with this isomer


    hydroquinone

    The 1,2 derivative is pyrocatechol, and the 1,3 derivative is resorcinol

  3. If no common name is used for the disubstituted benzene (as above), when a common name is used with one or both of the substituents, the substituent of higher preference is used to give the root name and the other substituent is named in a prefix.


    2-nitrobenzoic acid, o-nitrobenzoic acid


    3-aminophenol, m-aminophenol


    4-methoxyaniline, p-methoxyaniline

Self Assignment Questions
Review Monosubstituted Benzenes

Next page : Multisubstituted Benzenes

Index


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