1 H NMR ( 400 MHz , DMSO - d 6 ) : δ [ ppm ] = 3 . 89 ( s , 3 H ) , 3 . 92 ( s , 3 H ) , 5 . 51 ( d , 2 H ) , 7 . 54 - 7 . 59 ( m , 2 H ) , 8 . 07 - 8 . 12 ( m , 3 H ) , 8 . 45 ( s , 1 H ) , 8 . 51 ( s , 1 H ) .