1 H NMR ( 300 MHz , CDCl 3 ) : δ ( ppm ) = 1 . 31 ( s , 9 H ) , 2 . 81 ( s , 1 H ) , 2 . 86 ( s , 1 H ) , 6 . 82 - 6 . 86 ( m , 4 H ) , 7 . 13 - 7 . 16 ( m , 4 H ) , 7 . 36 - 7 . 43 ( m , 3 H ) , 7 . 53 - 7 . 70 ( m , 4 H ) .