Orgo Question

Jacob_Arulandu

Could someone explain this to me? Does the decarboxylation occur to any ketone in heat or is this just because it is an amino acid? Also is there a particular mechanism I could reference to understand how and why this process occurs?

Ae-Ri

Hi Jacob.

So this is an interesting question, because it does seem like you had to know this fact to get the correct answer. But digging a bit deeper, there's some strategy we can employ instead, because I don't know how valuable it is to know this fact. We're told that the sidechain of this amino acid is an acetyl group, which means that the entire amino acid looks like this:

We're then told that we're heating it up, which is a pretty harsh condition. I'm thinking things being "broken" rather than bonds being formed. So the question then becomes which part of this molecule is most "susceptible" to a reaction? My eye is drawn to the carbonyl carbon in the carboxylic acid as well as the ketone. However, between those two, the carboxylic acid carbonyl carbon is more reactive, since I have the OH group drawing electron density away, which makes it partially positive charged. The only answer choice that talks about that part reacting is (D), which is bonds broken. Do I know for sure that it's a decarboxylation? Not really. But none of the other answer choices really work. In order for (A) to work, it would require an enzyme - I don't know of any reactant that would isomerize a compound. Epoxide formation in (B) is a cyclic ether, and I'm not really sure how that would work without significant rearrangement, plus that requires bond formation. Heterocyclic ring in (C ) means a ring with something other than carbon, and if (B) doesn't work, neither does (C ). Does that help?