= Solution
\b[The product-forming pairing is $n(\mathrm{EtO^-})\to\pi^*(\mathrm{C=O})$.] 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, $n(\mathrm{ester\ O})\to\mathrm{empty\ Li}$, 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.
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