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17.8: Synthetic Strategies for Di-substituted Benzenes

  • Page ID
    183082
  • Synthetic Considerations

    To develop multiple step syntheses for di-substituted benzene derivatives, the regiochemistry of the substituents will determine the order of the reactions.  The directing effects of the benzene substituents are summarized below.

    ch 18 section 8 EAS Substituent Effects Summary.png

    The limitations of the Friedel-Crafts reactions must also be considered.  Friedel-Crafts alkylation and acylation reactions can only occur on benzene rings or benzene rings with ortho-, para-directors (activated rings or rings with halogens).  Even though both acyl and nitro groups are meta-directors, benzene would need to be acylated before it is nitrated.  To synthesize 3-nitroanisole [1-(3-nitrophenyl)ethan-1-one], the top reaction sequence is needed.  The bottom reaction sequence will not produce the desired product as shown in the two synthetic pathways below.

    ch 18 sect 8 example.png

    Exercise

    22. Starting with benzene and using any synthetic reagents, propose a multiple step synthesis for each of the following compounds.

    ch 18 sect 8 exercise.png

     

    Answer

    22.

    ch 18 sect 8 exercise solution.png

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