@aldol16 might help you on this one, but based on what i know, the carbonyl carbon is more electrophilic than a tertiary one. Because the oxygen is closer to the electrons (sp2 hybridized) thus pulling electrons harder toward it making the Carbonyl carbon more electrophilic (electron loving , since electron are being pulled away from it). Whereas the other compound is sp3 hybridized, so the electron are far away from the nucleus.
