The energy barriers for the cis-trans isomerization are obtained for a sample of push-pull compounds. The appropriate trend in the values for the barriers is obtained after an instability treatment of the restricted Kohn-Sham solution. At the instability zone, some compounds exhibit a singlet open-shell configuration. The width of the instability region around the transition state is characterized in an asymmetric push-pull compound. These results show that the instabilities in the twisted configuration of double bonds are mainly related to spin symmetry effects rather than to the molecular symmetry. For the open-shell singlet, an ensemble model is used to compute the electronic properties. The singlet-triplet energy gap along the rotation coordinate is qualitatively described by the use of spin potential and hardness. (C) 2003 American Institute of Physics.