# Glycoside Formation Reaction

Whenever we add $\ce{H+}$/ Ethanol to glucose in its hemiacetal form, why doesn't pinacone/pinacolone rearrangement take place in place of nucleophillic substitution. The product would lead to formation of a carbonyl bond and so, should be the favoured product.

The actual pathway is:

But, why can't the reaction occur like this with ethanol as a polar solvent?:

• Not on topic, but I feel like it would be a disservice to you to not point this out: your curly arrows for the first step (protonation and loss of water) aren't correct. The protonation and loss of water should also be two separate steps. I would also prefer to depict carbocations adjacent to oxygen with the alternative resonance form on the right: $$\ce{>C^{+}-OH <-> >C=O^+H}$$ – orthocresol Aug 8 '17 at 8:53