1 H NMR ( 300 MHz , CDCl 3 ) δ 1 . 24 ( 6 H , d , J = 7 . 2 Hz ) , 1 . 31 ( 12 H , s ) , 2 . 78 - 3 . 02 ( 1 H , m ) , 6 . 11 ( 1 H , d , J = 18 . 1 Hz ) , 7 . 20 ( 2 H , d , J = 7 . 9 Hz ) , 7 . 31 - 7 . 47 ( 3 H , m ) .