[LHM]

CH3CH2OCH2CH3, diethyl ether, has a boiling point of 308 K, while CH3CH2C=OCH3, butanone, has a boiling point of 353 K. But since technically diethyl ether has a larger mass wouldn't it be more polarizable, which usually means stronger London forces and a higher boiling point? Why is it that butanone has a higher boiling point though?

[onenameless]

That's because butanone is a ketone. The ketone in this case has a higher boiling points than the ether because it's more polar. In most cases actually, ethers have lower boiling points than other oxygen bound carbons like carboxy acids, alcohols and aldehydes. especially when you compare a ketone and an ether that both have 4 carbons. The ketone here has an oxygen bound to one carbon, so the two lone pairs of electrons that the oxygen has that are NOT bound to anything (lone pairs) are on the same side (like you would see in a water molecule) making one side slightly more negatively charged than the side which is bound to carbon. In an ether, you have both lone pairs of electrons on opposite sides to each other (one above, one below) which distributes the slight charge creating a weak polarity, and you have 2 carbons bound to it which makes it difficult for any other molecule to bind to it, thereby making it easier to break molecular interactions with that ether = lower boiling point.