Ninhydrin amino acid question

[tiny529]

Here's another one... =)

 

An unknown amino acid was treated with ninhydrin in -OH/H2O. On completion of the reaction, a compound that gave a positive Tollens test was isolated from the product mixture. Its 1H NMR spectrum exhibited resonances at 1.10 (d, 6H), 2.20-2.60 (multiplet, 1H), 9.60 (d, 1H) ppm, and three distinct signals were present in its 13C NMR spectrum. Draw the structure for the unknown amino acid. Do not draw the zwitterionic form.

 

Now, I drew 2-amino-2-methylpropanoic acid as the unknown. I figured that would give 2-methylpropanal when treated with ninhydrin. That would give a positive Tollens test, three 13C NMR signals, and the appropriate 1H NMR signals.

 

Am I missing something? This program HAS marked some of my structures wrong that weren't wrong. I actually drew one of them 4 times (I was 100% sure that I was right!) before it took it. =\

[Horza2002]

Unfortunately, it cant be 2-amino-2-methyl propionic acid (see my file). You will get acetone from this and not 2-methylpropanal. So far, you have four carbon atoms in the start material and four in the final product...there is a decarboxylation step in the mechanism and so you lose one of those carbons.

 

You are very close though...the NMR does indeed correlate good with 2-methylpropanal...so I would go with that being the correct aldehyde...so all you need to do is work backwards to get the amino acid....you where VERY VERY close to the correct anwser though...I'll give you a hint, its a proteinogenic amino acid.

Edited March 17, 2011 by Horza2002

[tiny529]

Unfortunately, it cant be 2-amino-2-methyl propionic acid (see my file). You will get acetone from this and not 2-methylpropanal. So far, you have four carbon atoms in the start material and four in the final product...there is a decarboxylation step in the mechanism and so you lose one of those carbons.

 

You are very close though...the NMR does indeed correlate good with 2-methylpropanal...so I would go with that being the correct aldehyde...so all you need to do is work backwards to get the amino acid....you where VERY VERY close to the correct anwser though...I'll give you a hint, its a proteinogenic amino acid.

 

Valine! Yay! Thanks! I'm sure that this is just the beginning of my questions. I've got 28 more to do by the weekend and they are ALL on chapters that we haven't dealt with yet. =(

[Horza2002]

Yep I got it as valine as well. That by no means that its 100% right, but the information you were given does indicate that you started with valine. If you have any more questions, just post them on here. I'm sure there are several of us on here who will be able to help you out.