Phản ứng isopren $+$ brom:
+ Cộng $1:1$
$CH_2=C(CH_3)-CH=CH_2 + Br_2 \buildrel{{-80^oC}}\over\longrightarrow CH_2Br-CBr(CH_3)-CH=CH_2$
$CH_2=C(CH_3)-CH=CH_2+ Br_2 \buildrel{{40^oC}}\over\longrightarrow CH_2Br-C(CH_3)=CH-CH_2Br$
+ Cộng $1:2$
$CH_2=C(CH_3)-CH=CH_2+ 2Br_2 \longrightarrow CH_2Br-CBr(CH_3)-CHBr-CH_2Br$