Why does acetone have a greater dipole moment than dimethyl ether? Below are the lewis structures for dimethyl ether and acetone. My chemistry textbook indicates that acetone has a larger dipole moment than dimethyl ether. I am familiar with dipole moments and the fact they are created by an unequal sharing of electron density. However I do not understand why acetone is more polar than dimethyl ether. My best guess is that having an extra carbon provides more electrons which allows the molecule to establish a larger difference in electron density between the oxygen and the rest of the molecule. I am unsure if this is correct and would greatly appreciate a more in depth explanation.

Dimethyl ether
The ether is fairly symmetrical though there is a bond angle of ~111°, "exposing" the oxygen on the side (and its electron cloud).  Acetone, however, has an oxygen off to the side, with its electron cloud offset ~120 picometers (pm), making it more polar.

Remember that oxygen is a strong electron acceptor, so that there will be a "lump" of electron probability surrounding it.



[Sorry about the hodgepodge illustration!]