1,2-Dinitroolefins undergo cis $\rightleftharpoons$ trans geometrical isomerization when reacted with HBr and $Br_2$. This isomerization reaction involves an bromine radical addition to the 1,2-dinitroolefin as part of the mechanism.
1,2-Dinitroolefins undergo substition rather than addition reaction with various nucleophilies, resembling aryl halides in behavior, and only one isomer was obtained.
From this nucleophilc substition reaction, the stereochemistry and the mechanism of 1,2-dinitroolefin was discussed.