Question

According to the Cahn-Ingold-Prelog system, the atoms with the highest ___ get the highest priority.

• A. Atomic mass
• B. Atomic number
• C. Altitude
• D. Atomic weight

Answer 1

The correct option is B Atomic number

The very first step is to find the chiral center. What is a chiral center? It is an $s{p}^3$ hybridized atom which is attached to four different atoms or groups. For example, the carbon atom is Bromochlorofluoromethane.

Now that there are 4 different groups, assign priorities (1, 2, 3, or 4) to the atoms directly bonded to the stereogenic center in order of decreasing atomic number. The atom of highest atomic number gets the highest priority (1).

Option ‘Altitude’ makes no sense but both atomic mass and atomic weight refer to the same thing. So the correct answer is atomic number.