Este có dạng $(C_nH_{2n-1}COO)_2C_2H_4$
$\Leftrightarrow C_{2n+4}H_{4n+2}O_4$
$\%C=60,6\%$
$\Rightarrow \dfrac{12.(2n+4).100}{12(2n+4)+4n+2+16.4}=60,6$
$\Leftrightarrow 1200(2n+4)= 60,6(28n+114)$
$\Leftrightarrow n=3$
Vậy axit là $C_3H_4O_2$
$\Leftrightarrow CH_2=CH-COOH$ (axit acrylic)