1 H - NMR ( 400 MHz , DMSO - d 6 ) δ : 8 . 48 ( 1 H , t , J = 6 . 4 Hz ) , 8 . 35 ( 2 H , d , J = 8 . 8 Hz ) , 7 . 97 ( 2 H , d , J = 8 . 8 Hz ) , 7 . 10 ( 2 H , d , J = 8 . 8 Hz ) , 6 . 79 ( 2 H , d , J = 8 . 8 Hz ) , 3 . 99 ( 2 H , d , J = 6 . 4 Hz ) , 3 . 69 ( 3 H , s ) .