From initial studies on exemplar molecules detailed in Table (see SI 2), the normal-coordinate vectors attributable to the first principal component mode correlate strongly with the maximum distortion of that mode, describing 0.90 -0.95 of the variance in the dataset. Beyond the second PCA mode, residual distortion is normally below the usual threshold for atom positional accuracy in crystallographic analysis. A simplified model of distortion for a molecule [e.g., boron dipyrromethene (BODIPY) distorts as aileron (A2) or butterfly (B2)] can be used as a convenient shorthand for the total distortion by symmetry arguments, for the first PCA mode A2 (1), and for the first normal mode A2( ), all having similar shape. No more than two parameters from each dissymmetric basis are required to generate a model as accurate as the measurement. This mirrors the way saddle and ruffle shapes (towards D2d) of porphyrin derivatives have a semantic, approximate meaning coincident with the symmetry coordinates and a fixed normal coordinate vector description. Across the structures indicated in Table , no meaningful relationships were found from chemical patterning to molecular shape beyond the first two parameters of each irreducible representation, excepting A1g, A1 or Ag. When different strategies are employedsteric hindrance, aromatic fusion or strap formation, for examplenew examples of molecules could still be modelled satisfactorily with combinations of these same two parameters. This finding is in line with our earlier findings on porphyrin macrocycles.