= Solution
\b[<ethanol> undergoes <proton transfer> with the <methoxide> produced.] The <oxygen> <lone pair> of <methoxide> attacks the hydroxyl <proton> of <ethanol>, while the <ethanol> O–H bond pair returns to its <oxygen>:
$$
\mathrm{MeO^-+EtOH\rightleftharpoons MeOH+EtO^-}.
$$
The <alcohol> acidities are similar, so this is an equilibrium, not an overwhelmingly one-way <deprotonation> determined solely by intrinsic acidity. The large <ethanol> reservoir and initially small <methanol> <concentration> nevertheless matter. This exchange means that <lithium ethoxide> need not be consumed stoichiometrically in the net transesterification. Neutral <ethanol> can also participate in <proton> shuttling; it is not acting as a reducing reagent or as a substrate for elimination under these conditions.
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