Why does 9-fluorenone dissolve in hexane?
Firstly, as a general rule, organic compounds with more then 6 carbon have higher London forces then polar forces.  This is a very general rule and doesn't work in all circumstances. Thus, this molecule is not as polar.

Secondly, cyclic compounds have much weaker London forces then molecules that have straight chains. Thus, this makes the London forces not so high(relative).

Thirdly, to have something dissolve in hexane it must have weak intermolecular forces, but not weaker then hexane itself, as hexane only has to suspend the solute molecules in solution and prevent the solute from clumping up and falling to the bottom.

So, quite simply, what happens is that the hexane molecules surround the 9-Fluorenone molecules, which diffuse through the solution.