A staggered Newman projection of 2-bromo-3-chlorobutane is viewed along C2-C3. The front carbon (C2) has $\mathrm{CH}{}_3$ at 12 o'clock, Br at 4 o'clock and H at 8 o'clock. The rear carbon (C3) has Cl at 6 o'clock, H at 2 o'clock and $\mathrm{CH}{}_3$ at 10 o'clock. Which is the correct name of the stereoisomer? (CIP priorities: Br above C, Cl above C.)

At C2 the priorities are Br, then C3, then $\mathrm{CH}{}_3$, then H. Exchange H with the rear carbon C3: H is then pointing away, C3 sits at 8 o'clock, and Br (4), C3 (8), $\mathrm{CH}{}_3$ (12) runs clockwise, i.e. R for the exchanged structure, so the real C2 is S. At C3 the priorities are Cl, then C2, then $\mathrm{CH}{}_3$, then H. Exchange H (2 o'clock) with the front carbon C2: C2 now sits at 2 o'clock and H points toward the viewer. Cl (6), C2 (2), $\mathrm{CH}{}_3$ (10) runs anticlockwise; because H points toward the viewer the true sense is clockwise, so the exchanged structure is R and the real C3 is S. The result is (2S,3S).