Try it on paper first. A hint, the key idea and the worked solution are here when you need them.
The methyl halides and have dipole moments of and . The bond lengths are for C-F and for C-Cl. Take and the charge of an electron as . Treat the molecule as two charges and at the ends of the bond. Find the share of one electron charge that is separated across each bond, as a percentage.
The dipole moment of a bond is the charge multiplied by the bond length, . One debye is . Boiling points of an unbranched series rise by nearly the same amount for each extra carbon atom. Percent yield is .
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Plan. Find and compare with .
Step 1. C-F. . Then . As a share of : .
Step 2. C-Cl. , so , which is of .
Answer: across C-F and across C-Cl.
Check. Fluorine is more electronegative than chlorine, so more charge is separated in C-F. The dipole moments are nearly equal only because the C-F bond is shorter.
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