Fig. 4. Visual representation of the chemical space: (a) principal component analysis of six physicochemical properties of pharmaceutical interest: molecular weight, hydrogen bond donors, hydrogen bond acceptors, the octanol and/or water partition coefficient, topological polar surface area, and number of rotatable bonds. (b) Principal Moment of Inertia (PMI) plot. The top left-hand corner of the PMI represents compounds with rod-like features (e.g., acetylene), the top right corner represents compounds with spherical features (e.g., adamantane), and the bottom corner represents compounds with disc-like features (e.g., benzene).