Salicylaldehydes readily Schiff bases with glycine. These schiff bases form bis(salicylideneglycinato) cobaltate (III) complexes. Twelve cobalt (III) complexes have been synthesized with substituents variously on the 3-, 4-, 5-, and 6-positions of the aromatic ring of the salicylaldehyde moiety. The carbon-hydrogen bond breaking reactions of the two gem-methylenic protons of the glycine moiety have been studied by deuterium exchange. Rates are first order in complex and first order in hydroxide ion. Rates differ for the exchange of the two protons, and their ratio varies from 0.81 to 4.7. This demonstrates a reversal of stereoselectivity, depending on ring substituents. Rates vs substituents generally follow Hammett behavior. The structural and electronic features that lead to stereoselectivity are discussed