The dielectric constant of DCM is 8.93 while chloroform is at 5. I don't think polarity would play a big factor as to why DCM doesn't dissolve iodine
as well. However after giving it much thought, perhaps it's the relationship between the opposing bonds of the DCM that makes it unreactive. The
chlorines will always align themselves opposite from one another when bonded to the carbon. Thus, the chlorine bonds in DCM should be vibrating at a
different frequency as compared to chloroform. These opposing chlorine molecules will vibrate with respect to one another. Taking a look at
chloroform, there's three chlorine molecules and a hydrogen. Thus, there will be more steric hinderance and the bonds will vibrate in a more unstable
fashion.
Therefore I propose the linear relationship between the chlorine molecules stabilize the molecule of DCM due to the bonds being able to vibrate at a
higher frequency. On the contrary, the trichloromethane will have bond bending due to the steric clash between the three chlorine molecules. The
inductive pocket that the three chlorine molecules create may perhaps be the reason that Iodine is able to be dissolved by chloroform. The lack of
this inductive pocket in DCM prevents the Iodine from reacting. |
