Fig. 5. Illustration of labeling atom types. Panel (A) shows an ethanol molecule with atoms colored by element: grey (C), red (O), white (H). Panels (B–D) illustrate the typing of different atoms in this molecule. In each panel, the chosen atom is colored green. Its first neighbors are colored yellow. Its second neighbors are colored blue. In Panel (B), the hydrogen in the hydroxy group is chosen as the central atom. It is connected to one oxygen that is connected to a carbon atom plus the central atom. In Panel (C), the α-H is chosen as the central atom. It is connected to one carbon that is connected to one hydrogen, one carbon, and one oxygen plus the central atom. In Panel (D), the β-C is chosen as the central atom. It is connected to three hydrogens and one carbon. The carbon is connected to two hydrogens and one oxygen plus the central atom.