1 H NMR ( 300 MHz , DMSO - d 6 ) δ 9 . 22 ( s , 1 H ) , 8 . 99 ( s , 1 H ) , 7 . 72 ( d , 2 H , J = 8 . 4 Hz ) , 7 . 62 ( d , 2 H , J = 8 . 7 Hz ) , 7 . 49 ( d , 2 H , J = 8 . 7 Hz ) , 7 . 34 ( d , 2 H , J = 8 . 4 Hz ) .