1 H NMR ( 400 MHz , chloroform - d 1 ) δ = 7 . 67 ( s , 4 H ) , 4 . 95 ( br s , 1 H ) , 4 . 82 - 4 . 79 ( m , 1 H ) , 4 . 07 ( dd , J = 8 . 8 , 8 . 8 Hz , 1 H ) , 3 . 94 ( dd , J = 8 . 8 , 6 . 8 Hz , 1 H ) , 3 . 56 - 3 . 54 ( m , 2 H ) , 1 . 38 ( s , 9 H )