Ethylene glycol to acetaldehyde-dehydration or a concerted mechanism

Two possible mechanisms have been proposed to account for the rearrangement of ethylene glycol to acetaldehyde. The first is a rearrangement with a hydride shift occurring in concert with the loss of a water molecule. The second is an acid catalyzed dehydration reaction proceeding through the enol to yield acetaldehyde. DFT calculations are presented which show the first postulation to be the lower energy pathway by a considerable margin.