Week 8 Condensed Answer Key

1. tetraphenylcyclopentadienone, benzil, dibenzyl ketone

2. The spatial arrangements of atoms in Benzil will have to be considered. Both structure A and B are planar. Conformation A would have a dipole greater than that of dibenzyl ketone. In Conformation B the individual dipoles of the carbonyl groups would cancel out. However, neither of these structures are correct.

The correct structure is where the carbonyl groups are not coplanar (see below). Thus as one rotates A around the C-C bond the individual dipoles of the carbonyl groups start canceling out. When you reach structure B the dipoles have completely canceled. So the correct structure is somewhere in between.