[tdod]

To, me it looks like benzophenone should be more polar b/c the symmetry of benzil's trans configuration should cancel the dipole... so, I can't figure out why Benzil is actually the more polar one.

Thanks!

[fledarmus]

There is no C-C double bond in benzil - it doesn't adopt a true trans configuration. Sterics between the ortho positions of the benzene rings prevent them from entirely overlapping in either cis or trans form. Instead, the carbonyls try to be coplanar with the benzenes, for the best conjugation to the aromatic system, and the bond between the two halves of the molecules is twisted to about 90°.

Does this help your vector addition any?

[orgopete]

I also think the alpha-dicarbonyl group will be more polar in general as this arrangement will make a carbonyl group more polar. I suggest this is similar to adding chlorine atoms to acetaldehyde. The carbonyl is more reactive and trichloroacetaldehyde prefers to exist as a hydrate with water. Hexafluoroacetone is similar.