1 H NMR ( 400 MHz , DMSO - d 6 ) δ [ ppm ] = 3 . 89 ( s , 3 H ) , 3 . 92 ( s , 3 H ) , 7 . 13 ( t , 1 H ) , 7 . 72 ( d , 2 H ) , 8 . 11 ( s , 1 H ) , 8 . 20 ( d , 2 H ) , 8 . 48 ( s , 1 H ) , 8 . 52 ( s , 1 H ) .