Final answer:
In amino acids, the substituents are ranked by atomic number, yielding a priority order of oxygen (O), sulfur (S), nitrogen (N), carbon (C), and hydrogen (H).
Step-by-step explanation:
In amino acids, the substituents are ranked according to their priority based on the Cahn-Ingold-Prelog rules. The five most common atoms you will encounter when considering amino acid structure are carbon (C), oxygen (O), nitrogen (N), hydrogen (H), and sulfur (S). When ranking these atoms in terms of priority, you will follow the atomic number, where the atom with the higher atomic number gets higher priority. Therefore, the order from highest to lowest priority is: oxygen (O), sulfur (S), nitrogen (N), carbon (C), and hydrogen (H). This ranking is important for stereochemistry considerations and when determining the configuration of chiral centers within amino acids.