Using a density-functional method we have calculated the electronic and structural properties of infinite and periodic (CF)(x), (CCl)(x), and (CFCCl)(x) chains. Only for the (CF)(x) and (CCl)(x) trans isomers without a C-C bond-length alternation we have optimized the structure completely and subsequently explored whether the total energy for these isomers could be lowered upon a such alternation. Finally, we studied the electronic properties of different cis isomers with fixed structures as well as of trans and cis isomers of (CFCCl)(x). Special emphasis is put on whether these newly synthesized materials have properties resembling those of most other conjugated polymers, i.e., whether pi orbitals from mainly carbon functions are those closest to the Fermi level and whether a bond-length alternation exists. We find that the F-substituted materials in many respects are similar to the unsubstituted ones (with, however, smaller differences), but that the Cl-substituted ones differ significantly from the unsubstituted ones. The trans isomers of the systems with mixed substitutions possess properties that are intermediate between those of the F- and the Cl-substituted ones. On the other hand, the cis isomers of (CFCCl)(x) have markedly different properties and are the only ones with F/Cl nearest neighbors. A comparison with the experimental information suggests that for (CFCCl)(x) the trans isomer is the one that is synthesized. Finally, we predict that only for (CF)(x) will solitons or polarons be generated upon doping.