1 H - NMR ( CDCl 3 , δ , ppm ) : 5 . 56 ( 2 H , s ) , 6 . 89 ( 1 H , td ) , 6 . 94 ( 1 H , d ) , 7 . 79 ( 1 H , td ) , 7 . 87 ( 1 H , d ) , 8 . 03 ( 1 H , m ) , 8 . 31 ( 1 H , s ) , 8 . 54 ( 1 H , d )