What is the absolute configuration of the following stereocenters?

• A. I: S, II: R
• B. I: R, II: S
• C. I: S, II: S
• D. I: R, II: R

Answer: (B)

Verified step by step guidance

1. Identify the stereocenters in the molecule. In the image, stereocenter I is the carbon bonded to Br, and stereocenter II is the carbon bonded to the ethyl group (CH2CH3).
2. Assign priorities to the substituents around each stereocenter based on atomic number. For stereocenter I, the substituents are Br, CH3, CH2CH3, and the hydrogen (not shown, but implied). For stereocenter II, the substituents are CH2CH3, CH3, the rest of the carbon chain, and the hydrogen (not shown, but implied).
3. For stereocenter I, assign priority: Br (highest atomic number) > CH2CH3 > CH3 > H. For stereocenter II, assign priority: CH2CH3 > CH3 > the rest of the carbon chain > H.
4. Determine the configuration by arranging the substituents in order of priority and observing the direction of rotation. For stereocenter I, if the lowest priority group (H) is pointing away, observe the sequence from highest to lowest priority. If the sequence is clockwise, the configuration is R; if counterclockwise, it is S. Repeat the process for stereocenter II.
5. Verify the configurations by considering the orientation of the lowest priority group. If the lowest priority group is not pointing away, reverse the observed configuration. Compare your findings with the given options to determine the correct absolute configuration for each stereocenter.