1 H NMR ( 300 MHz , DMSO - d 6 ) δ 10 . 56 ( s , 1 H ) , 9 . 59 ( s , 1 H ) , 8 . 14 ( d , 2 H , J = 8 . 2 Hz ) , 7 . 92 ( d , 2 H , J = 8 . 2 Hz ) , 7 . 78 ( d , 2 H , J = 8 . 7 Hz ) , 7 . 67 ( d , 2 H , J = 8 . 7 Hz ) , 5 . 80 ( s , 2 H ) .