I have read that under mildly acidic or alkaline conditions alcohols can attack aldehydes/ketones to produce hemi-acetals. But the reaction is reversible, so the reactants and the hemia-cetal are in equilibrium. Let's say I have a solution of methanol to which I add mildly acidified glucose solution. In theory, a hemi-acetal should have formed. Now if I warm the solution for some time so that the methanol evaporates, the hemi-acetal should decompose back to maintain equilibrium. So I wouldn't be able to isolate such a compound. What experiment can I run then, to confirm the formation of the hemi-acetal?
What I have thought: Maybe I can use IR spectroscopy to confirm the presence of a new bond but considering the solvent is water, it seems infeasible to do this.