Condensation of an ester enolate with another ester molecule affords a b-ketoester. This reaction is named the Claisen condensation (Section 14.3A). If the two ester molecules are not identical, the reaction is called the crossed Claisen condensation, and as many as four different products can result (Section 14.3C). A crossed Claisen using one ester without hydrogen atoms attached to the carbon immediately adjacent to the ester carbonyl group (H-C-C=O; called beta hydrogens) is necessary to avoid this problem. An intramolecular Claisen condensation is called the Dieckmann reaction (Section 14.3B).