 Solution

The product-forming pairing is $n(\mathrm{Et}{\mathrm{O}}^{-})\to {\pi }^{\ast }(\mathrm{C}=\mathrm{O})$. Orient an occupied ethoxide oxygen lobe toward the large carbon lobe of the carbonyl acceptor with matching phase. An oblique approach permits constructive overlap while the pi bond weakens; this is the usual Bürgi-Dunitz trajectory to acyl carbon. The high-energy occupied orbital on the anion makes ethoxide the stronger electron-pair donor than the neutral ester oxygen.

The reverse frontier pairing, $n(\mathrm{ester}\mathrm{O})\to \mathrm{empty}\mathrm{Li}$, gives oxygen-to-lithium coordination. It is a plausible stabilizing contact and can coexist with the first interaction, rather than constituting an alternative way to replace the ester alkoxy group. In the elementary frontier picture, the anionic donor-to-carbonyl interaction is the important pairing for the new covalent bond and is favoured by its donor strength and appropriate accepting coefficient at carbon. The Li contact can polarize the carbonyl and organize the reacting pair. Precise energy-gap rankings require a specified solvated lithium species; the sketches alone do not justify pretending that lithium coordination cannot occur.