  We study equations for the mechanical movement of chains of identical
particles in the plane interacting with their nearest-neighbors by bond
stretching and by van der Waals and Coulomb forces. We find collinear and
circular equilibria as minimizers of the energy potential for chains with
Neumann and periodic boundary conditions. We prove global bifurcation of
periodic brake orbits from these equilibria applying the global Rabinowitz
alternative. These results are complemented with numeric computations for
ranges of parameters that include carbon atoms among other molecules.
