There is minimum connection time, and there is sensible connection time. 39 minute connection at ORD meets the minimum, but I don't consider it sensible, and its a no-go if you have to change terminals. Any delays on SEA-ORD and your connection is kaput. Keep in mind you need to be present at the gate when boarding starts (usually 30 minutes prior to departure) so you really have only 9 minutes to get to your gate for the AY flight.