Question 22

[Guest]

In question number 22, I don't see where hydrolysis is occuring. Where is the OH group adding to make a carboxylic acid?

Thank you!

[admin]

Of course, hydrolysis litterally means the adding of water (hydro) in order to break apart a molecule (lysis). In other words, even without knowing the mechanism, just by the fact that in the last step, acidic water is added to a molecule that clearly breaks apart, should alert you to the fact that hydrolysis is happening. And that is the limit to what you would be expected to know to solve that aspect to this problem.

But just for fun, we'll go further. To begin with, all the products of the final reaction are not present (the other organic product is not there). So when I do orgo, I often start by looking at the most charged species to see what it would do. Well we have H+ so it will be attracted to the delta negative oxygens. The only stable intermediate would be if it attacks the carbonyl oxygen to the right of the molecule creating an -OH and a formal positive charge on the central carbon which is now the most charged species. So, similar to acetal/ketal formation, the oxygen of the water (H2O) attacks the positive carbon creating a tetrahedryl intermediate. When the carbonyl group is reformed (kicking out the catalyst proton) -OC2H5 would normally have to leave but if the heat is tremendous, perhaps the carbon-carbon bond would break (not something that you would be asked to deal with on the MCAT but when the question clearly points to hydrolysis then you roll with it).