1 H - NMR ( 400 MHz , DMSO - d 6 ) δ : 8 . 79 ( 1 H , s ) , 8 . 15 ( 2 H , d , J = 7 . 2 Hz ) , 7 . 79 ( 2 H , d , J = 8 . 8 Hz ) , 7 . 65 ( 2 H , d , J = 8 . 8 Hz ) , 7 . 51 ( 2 H , d , J = 8 . 8 Hz ) , 4 . 09 ( 2 H , s ) .