1 H - NMR ( 400 MHz , DMSO - d 6 ) δ : 8 . 40 ( 1 H , s ) , 8 . 15 ( 2 H , d , J = 8 . 8 Hz ) , 7 . 80 ( 2 H , d , J = 8 . 4 Hz ) , 7 . 66 - 7 . 56 ( 3 H , m ) , 7 . 53 ( 2 H , d , J = 8 . 8 Hz ) , 4 . 15 ( 2 H , d , s ) .