Which of the following structures has the R configuration

Which of the following structures has the R configuration? H OH H3C Cl CH2CH3 H3C H3C H CH2CH3 OH H3CH2C H A) Only I and II B) Only II C) I, II and III D) Only I

The Correct Answer and Explanation is:

To determine which of the structures has the R configuration, we need to follow the Cahn-Ingold-Prelog priority rules. The priority of substituents attached to the chiral center is assigned based on atomic number, with higher atomic numbers receiving higher priority. After assigning priorities, we need to check the orientation of the groups around the chiral center to see if they follow the R or S configuration.

Here’s how we’ll evaluate each structure:

1. Structure I:
   • The central carbon is attached to a Cl, OH, CH3, and CH2CH3 group.
   • Assigning priorities:
     • Cl (atomic number 17) takes priority 1.
     • CH2CH3 (ethane group) takes priority 2.
     • OH (oxygen) takes priority 3.
     • CH3 (methyl group) takes priority 4.
   • After determining the priorities, if the groups are oriented such that the lowest priority (CH3) is pointing away from you and the sequence of the other three groups goes in a clockwise direction, the configuration will be R.
2. Structure II:
   • The central carbon is attached to a Cl, OH, CH3, and CH2CH3 group.
   • The priorities assigned to the groups would be identical to those in Structure I.
   • Similarly, if the lowest priority group (CH3) is pointing away and the other groups follow a clockwise direction, the configuration is also R.
3. Structure III:
   • The central carbon is attached to CH3, CH2CH3, OH, and another CH3 group.
   • Again, we assign priorities in the same manner. The OH group will likely have a higher priority than the methyl and ethyl groups.
   • If the lowest priority group (one of the CH3 groups) points away and the others follow a counterclockwise direction, the configuration is S.

Conclusion:

Based on the analysis, both Structure I and Structure II follow the R configuration. Structure III, however, has the S configuration. Thus, the correct answer is:

A) Only I and II.

This analysis relies on correctly determining the priorities and ensuring the lowest priority group is pointing away from the viewer to check the clockwise or counterclockwise rotation of the groups.