Relaxation properties of three isomers of atactic polychlorostyrene, having the chlorine atom in the ortho, meta, and para positions (P2CS, P3CS, and P4CS, respectively), were measured by mechanical and dielectric spectroscopies and modulated scanning calorimetry. For the alpha relaxation, the more spatially extended pendant group in P4CS gives rise to steric constraints on the segmental dynamics that cause both the temperature dependence of its relaxation time (i.e., the fragility) and the number of dynamically correlated segments to be largest. For the secondary beta-relaxation in P4CS, the chlorophenyl moiety can rotate (spin) without involving the backbone; that is, the motion involves internal degrees of freedom. Consequently, this secondary relaxation is high in frequency and has a weak relaxation strength, especially as measured dielectrically. On the other hand, the pendant group in P2CS cannot reorient without adjustments in position of the backbone segments, causing its beta relaxation strength measured mechanically to be the largest. Since all atoms in the repeat unit for P2CS participate in the secondary dynamics, it is classifed as a Johari-Goldstein (JG) process. As generally found for JG relaxations, the behavior of the beta relaxation in P2CS is affected by the density changes accompanying physical aging.