3,4-dichlorohexane: A Meso Compound?

[Chem_Mod]

Question: For 3,4-dichlorohexane, how is it a meso compound when the hydrogens bonded to each of the carbons are not in the same plane, one is dashed and the other is a solid wedge. When classifying something as a meso compound, do you take the planes into consideration. Also, the solution manual drew a hydrogen and a chlorine on the dashed wedges and when they drew the fisher projection, both the hydrogens were placed on the left side of both the horizontal lines. Is there a reason for that?

[Chem_Mod]

Answer: A meso compound contains stereocenters, but overall it is not chiral. The bonds in 3,4-dichlorohexane are all single bonds and therefore are all free to rotate. Make this molecule with your model kit and rotate it to see the mirror plane. The fisher projection can have the hydrogens on either the left or the right side, however they must both be on the same side if it is meso. Remember a fisher projection can be rotated 180 degrees in the plane of the paper and give the same molecule.