phthalic acid (thing)

structural formula of phthalic acid:

             H

             |

             O

              \ 

      H        C == O

       \      /        

        C == C        O -- H

       /      \      /

 H -- C        C -- C

       \\    //      \\

        C -- C        O

       /      \

      H        H        phthalic acid

                        C8H6O4