Question

According to the Cahn-Ingold-Prelog (CIP) rules for assigning R and S configurations to stereocenters, which of the following substituents has the highest priority?

1) Methyl group
2) Ethyl group
3) Propyl group
4) Butyl group

Answer 1

When assigning R and S configurations according to CIP rules, the substituent with the longest carbon chain has the highest priority. Therefore, among methyl, ethyl, propyl, and butyl groups, the butyl group has the highest priority due to its longer carbon chain.

Step-by-step explanation:

According to the Cahn-Ingold-Prelog (CIP) rules for assigning priority to substituents at a stereocenter, the substituent with the highest priority is the one with the greatest atomic number attached directly to the stereocenter. When comparing substituents like methyl, ethyl, propyl, and butyl groups, which are all comprised of carbon and hydrogen atoms, priority is determined by the longest carbon chain. Thus, the priority increases with the length of the carbon chain.

Following this principle:

1. Methyl group (–CH3)
2. Ethyl group (–CH2CH3)
3. Propyl group (–CH2CH2CH3)
4. Butyl group (–CH2CH2CH2CH3)

Therefore, between the methyl, ethyl, propyl, and butyl groups, the butyl group has the highest priority because it has the longest chain of carbon atoms, which means it has a higher molecular weight compared to the others.