Question

which of these structures shows how the pictured molecule will look after it is rotated by $180^{\circ}$, as illustrated?note: only check the boxes of structures that correspond to a single $180^{\circ}$ rotation of the original structure. ignore structures that have been rotated or flipped multiple times or in other ways.

Explanation:

Step1: Identify rotation effect

A 180° rotation inverts the position of all substituents relative to the chiral centers, and reverses the direction of wedged/dashed bonds for each group while maintaining the overall connectivity of the molecule.

Step2: Match original to rotated structure

Compare the original molecule:

• Left chiral center: $CH_3$ (wedged), $H$ (dashed), $OH$ (wedged), $CH(OH)C(CH_3)=NCH_3$
• Right chiral center: $C(CH_3)=NCH_3$, $H$ (wedged), $OH$ (dashed), $CH(CH_3)OH$

After 180° rotation, the rightmost structure in the top row (third option) matches: the $C(CH_3)=NCH_3$ group moves to the left end, and all wedged/dashed bonds are inverted appropriately to reflect the 180° turn, while the connectivity of atoms remains identical to the original.

Answer:

Third top option:

     OH  H
      \ /
C(CH3)=N-C-C(CH3)
          \ /
           H  OH
            \
             CH3

(Structural description: Left end is $C(CH_3)=NCH_3$, followed by chiral center with wedged $H$, dashed $OH$, then chiral center with wedged $OH$, dashed $H$, ending with $CH_3$)