Question

Which among the following functional groups has been given the highest priority while assigning R-S configuration?

• A. -C$_6$H$_5$
• B. -CN
• C. -C$_2$H$_5$
• D. -CH$_3$

Answer 1

Answer: (B)

-CN

Answer 2

Using the Cahn-Ingold-Prelog priority rules:

• All groups have carbon as the atom attached to the chiral center.
• For -CN, the carbon is triple-bonded to nitrogen. This is treated as the carbon being attached to three nitrogen atoms (atomic number 7), which is higher than the atoms attached in the other groups.
• Thus, -CN gets the highest priority.