We consider a family of molecular liquids, each consisting of linear molecules with N covalent bonds, focusing specifically on N = 1 (diatomic liquid), N = 3 (four-atom molecular liquid), and N = 200 (macromolecular liquid). The bonded and nonbonded potentials, u(b)(r)and u(nb)(r), are the same for each system, with ub representing stiff linear springs and unb corresponding to the repulsive portion of the Lennard-Jones potential. The relaxation of the stress difference sigma, following a constant-volume elongation of the system, is determined in terms of interatomic interactions by nonequilibrium molecular dynamics simulations. It is found that the nonbonded interactions make the principal contribution to sigma while the bonds make a negative contribution. For all systems studied it is found that, following a short induction period after the start of relaxation,sigma = C<>, where <>(t) decays. An explanation of the broad applicability of the relation sigma = C<> is presented in terms of the concepts of steric shielding, intrinsic interaction distributions, and intrinsic stresses. The failure of this relation during the short induction period is explained in terms of anisotropies in atom distributions present immediately after deformation.