This configuration space is symmetric about the z-axis and hence, without additional reference points, all A-2 polytopes are equivalent. Put another way, the x-and y-axes are arbitrary. Both internal and external frames of reference can fix the x-and y-axes. For example, a water molecule in an external static electric field suffices as an external frame of reference to a minimal AB2 system. Alternatively, the additional structure of a more complex molecule provides an internal frame of reference. In Fig. are shown four molecular systems 1 -4 that undergo polytopal rearrangements at the central coloured bicoordinate centre. These polytopal rearrangements represent trajectories through the AB2 L-2 Π 𝑢 -mode 𝒞 ̅ 2 configuration space as shown on the right of Fig. . These correspond to the hula-twist (1), bond-angle reflexion (2) , half hula-twist (3) [16], and delocalised-linear (4) . Animations of the DFT-modelled polytopal rearrangements for 1 -3 are provides in the Supplementary Information. Examples of chemical systems exhibiting AB2 polytopal rearrangements and their trajectories through the AB2 L-2 Π 𝑢 -mode 𝒞 ̅ 2 configuration space. Compound 1 exhibits the "Hula-twist" motion (cyan circular trajectory). Compound 2 exhibits Bond-Angle Reflection (magenta meridional track). Compound 3 exhibits a "half hula-twist" motion (dark blue half circular track). Carbon suboxide 4 exhibits random delocalised bending motions (orange polar region).