1 H NMR ( 400 MHz , DMSO - d 6 ) δ [ ppm ] = 3 . 87 ( s , 3 H ) , 3 . 90 ( s , 3 H ) , 6 . 56 ( d , 1 H ) , 7 . 55 - 7 . 60 ( m , 2 H ) , 7 . 83 ( d , 1 H ) , 7 . 92 - 7 . 96 ( m , 2 H ) , 8 . 48 ( s , 1 H )