So I just got an Orgo test back that I did rather poorly on. One question asked for the mechanism of attaching ethylene glycol as a protecting group onto a particular molecule that an ester and a ketone. I drew the ethylene glycol as protecting the ketone portion of the ester (forming a five-member, two-oxygen ring). However, when I got the test back, it turns out that the protecting group would instead protect the ketone (not even an aldehyde, a ketone). I can't figure out why it would eschew the ester in favor of the ketone. Anyone know?
Not really sure... it's been several years since I've played with organic chem. Just a stab in the dark, is it possible it might have something to do with the chirality of the bonding site?
Figured it out (more accurately, asked my orgo professor) - the extra oxygen in the ester is electron donating enough that it makes the carbon in the ester too nucleophilic for the oxygen in the ethylene glycol to attack it; that is to say, due to the extra oxygen, the carbon is no longer electrophilic enough for the ethylene glycol to attack. The ketone, not having that extra oxygen, is ripe for a nucleophilic attack by the ethylene glycol.