Q. 48

[yfangl097543]

There are many esters in the molecules, so wouldn't all of them be capable of being labeled by nucleophilic attack by the water and elimination of the unlabeled oxygen?

[admin]

You could have a point if there were "many esters" but I don't see any esters amoung the molecules presented. Recall: an ester has the general formula O=COR This formulation is nowhere in Figure 1 or question 48.

[soljahgurl1971]

I'm not sure I understand how to work this question. I read the explanation and I still don't understand.

[admin]

If you tell me exactly what part of the problem you don't understand, I could be more helpful.

If you have The Gold Standard text, the reverse reaction is represented in ORG 7.2.3; tracing oxygen in a reaction is shown for esters in ORG 9.4.

You may also want to review your organic mechanisms: www.goldstandard-mcat.com/organic-chemistry-mechanisms

[soljahgurl1971]

[admin]

Well, the question is just asking: which of the following products was made with water? Answer choice A is a reactant in the passage with water so that can't be the answer. Answer choice D is at the bottom of Figure 1, unrelated to water in the reaction provided.

We are left with answer choices B and C which are both products involving water in the 3rd line of the mechanism provided. Be carefully examining the reactant, you will notice that answer choice B got the H's from water and answer choice C got the O from H2O. Since the O is radiolabelled, it will show up in answer choice C.

[quadalpha]

Perhaps this question would be clearer if it mentioned that the ninhydrin reaction sequence is carried out in labeled water. As it is, it can be read to mean, "Which of these compounds would be labeled if it is put into labeled water?"

[mcat_premed3832]

You are correct that the question should make direct reference to the passage or the ninhydrin reaction. This has been changed.