Given the following molecule, what is the absolute configuration of the chiral center at carbon 2? (Assume the priorities are assigned according to the Cahn-Ingold-Prelog rules: $1$ = $\mathrm{Br}$, $2$ = $\mathrm{OH}$, $3$ = $\mathrm{CH}{3}_3$, $4$ = $H$, with the lowest priority group pointing away from you.)

• A. $S$
• B. $R$
• C. Neither $R$ nor $S$ (achiral)
• D. Cannot be determined from the information given

Answer: (B)

Verified step by step guidance

1. Identify the four substituents attached to the chiral center at carbon 2 and assign their priorities according to the Cahn-Ingold-Prelog (CIP) rules. Here, the priorities are given as: 1 = Br, 2 = OH, 3 = CH3, and 4 = H.
2. Orient the molecule so that the substituent with the lowest priority (priority 4, which is H) is pointing away from you. This means you are looking down the bond from carbon 2 to the hydrogen atom.
3. Trace a path from the substituent with the highest priority (1, Br) to the second highest (2, OH), and then to the third highest (3, CH3).
4. Determine the direction of this path: if the path goes clockwise, the configuration is R; if it goes counterclockwise, the configuration is S.
5. Confirm that the lowest priority group is indeed oriented away from you to ensure the configuration assignment is correct. If it is not, reverse the configuration determined in the previous step.