Fig. 3. Potential energy profiles for the 2′ and 3′-catalyzed reactions of CHO with CO₂. Each transition state and intermediate is designated in the proposed reaction pathway (Scheme 2). Computations were performed at the ωB97XD/6-31G* level with the self-consistent reaction field (SCRF) method (Et₂O). The potential energies relative to reactant complex R are given in kcal mol^–1. The energies of CO₂ and the second CHO are included in the former steps where they do not appear explicitly in the computational model.