1 H - NMR ( 400 MHz , CDCl 3 ) δ : 7 . 81 ( 2 H , d , J = 6 . 8 Hz ) , 7 . 50 ( 2 H , d , J = 8 . 8 Hz ) , 7 . 32 - 7 . 28 ( 3 H , m ) , 7 . 21 ( 2 H , d , J = 7 . 6 , Hz ) , 4 . 69 ( 1 H , s ) , 4 . 186 ( 2 H , d , J = 6 . 4 Hz ) .