Diacetic acid 5-methyl-6-oxo-2,4-cyclohexadien-1-ylidene ester

    Parameter     ppm  Hz

      D(A)         6.54
      D(B)         6.28
      D(C)         6.02
      D(D)         1.93
       J(A,B)          6.1
       J(A,C)          1.7
       J(A,D)          1.4
       J(B,C)          9.9
       J(B,D)          0.4
       J(C,D)          0.8
     
      D(E)         2.04
     
     BUBB,W.A. ET AL. ORG.MAGN.RESON. 9, 167 (1977)