2-chloro-1,3-butadiene is the monomer and it has the formula C4H5Cl. I'd assume that different isomers could be 1-chloro-2,3-butadiene, 1-chloro-2,4-butadiene, and 2-chloro-1,4-butadiene, though I'm not postive.
There are two structural isomers - one with three fluorine atoms on one carbon, and...