Enolate anions are formed when a carbonyl compound containing an alpha-hydrogen is treated with a base. The less hindered alpha-hydrogen is removed more rapidly. There a couple of different paths that this reaction can take. The paths are dependent upon the amount of ketone present and the strength of the base used. Lithium diisopropylamide (LDA) is a very strong base, which is capable of driving the reaction to the right. See reaction below.
At this point, there is no equilibrium established. If all of the LDA is used up and there is excess ketone, then a second reaction can occur. It is here that equilibrium can be established. See the corresponding reaction below. The more stable enolate anion predominates. Recall, that the stability is based on the degree of substitution of the double bond in the enolate anion. The carbon-carbon double bond, which is more substituted, is more stable and will predominate in the reaction. If all of the ketone is used up, the reaction goes to completion.
