Guideline for Writing Organic Molecule Isomers and Determining Number of Rings Plus Pi-Bonds

Steps (1)–(3): Construct a partial molecule (e.g., a continuous chain) of all central atoms (atoms which take more than one bond in organic molecules): C, N, O, P, S. Follow normal neutral bonding rules; provide octet bonding for S (two bonds) and P (three bonds) unless other information is available.